WTF?
That's what radio astronomer Anna
Capinska labeled the image of an
enormous mysterious blob she first
spotted in 2019.
Billions of years from Earth in the
realms of deep space. It appeared like a
ghostly ring of smoke, a glowing oddity
of radio waves that didn't appear to
match up with any known supernova
remnant or galactic interaction. What in
the world in the universe could this be?
It may have been unusual, but this
object was not alone. named odd radio
circles or orcs. The objects we have
found seem to encompass everything we
struggle to explain in the cosmos. Five
orcs have been confirmed since
Kapinska's first finding, and several
more blobs may fit the profile. What
cosmic force is so powerful that it
could sculpt a ring of energy a million
lightyears wide, so vast it dwarfs our
Milky Way by a factor of 10? Are these
radio rings the relics of galactic
rebirth or the dying echoes of something
we have yet to comprehend? And why
haven't we found more of them?
I'm Alex Mccoan and you're watching
Astram. Join me today as we attempt to
unravel one of modern astronomy's
greatest mysteries and reveal the four
leading hypotheses that could unlock the
origin of these objects so odd they defy
even the universe's standards.
This mystery first began as a result of
modern technology. Around the turn of
the new millennium, technological
advancements in radio astronomy
drastically increased the number of
known radio sources from just a few
hundred thousand to a couple million.
For decades, nobody was able to
significantly increase that number. That
is until recently. Radio astronomy was
due for another upgrade. and Australia's
National Science Agency, the
Commonwealth Scientific [music] and
Industrial Research Organization,
oversaw the launch of the revolutionary
Australian Square Kilm Array Pathfinder
Telescope, or ASCAP, one of several new
radio telescopes coming online at the
time. With 36 radio dishes that are each
12 meters across, what makes the Western
Australia radio telescope special is its
phased array feed, which allows it to
image huge areas of the sky at once.
Unlike the previous generation of radio
telescopes, ascap's field of view is an
impressive 30 square°, the equivalent to
the surface area of about [music]
150 moons as seen from Earth. The phased
array feed allows astronomers to ignore
radio signals from things like
satellites, which can otherwise create
blind spots for radio telescope
receivers.
With this new generation of telescopes,
radio astronomers are able to detect
even faint diffuse objects. Western
Sydney University professor Ray Norris
of Zero, later leading the original org
discovery, predicted that the Australian
Telescope's evolutionary map of the
universe project or emu would be part of
an extraordinary increase in our
knowledge of radio sources across the
universe. The project is named after the
emu in the sky, a constellation of dark
nebula rather than stars in the Milky
Way galaxy, which has been recognized in
Aboriginal astronomy for generations.
All of the radio sources discovered up
to that point by every radio telescope
in the entire history of radio astronomy
amounted to about 2.5 million sources.
And the emu project alone was expected
to increase that total to 70 million
radio sources. Keep in mind that only
represents the discoveries that were
expected to come from just one of the
new radio astronomy telescopes. Norris
was certain that all of this new data
would deliver some major surprises and
it did much sooner than anyone expected.
The EMU project looked at large areas of
the sky that other telescopes had not
imaged yet and collected vast catalogs
of data. So much that scientists
expected they would need the help of
machine learning to sift through it all.
But it was in the process of browsing
through some of the project's
preliminary images that Capinska, the
radio astronomer who discovered orcs,
would first notice the oddly shaped
radio emissions using her old-fashioned
human eyes. To me, that makes this
discovery all the more special. Even
with vast amounts of data and machine
learning tools, this is an example of
how human curiosity will always be an
integral part of the scientific process.
While browsing these early emu images,
Kapinska started to notice some strange
shapes that she couldn't identify as any
known space object. On an image of one
of these odd shapes, a circle of radio
emissions like a giant smoke ring
floating in distant space, she wrote the
label WTF,
encapsulating just how baffling this
was. Kapinska had never seen anything
like it. After sharing her strange
discovery with colleagues, a team of
radio astronomers, including Norris and
Emile Len began sifting through the
images, searching for more of these
circular radio blobs. Len found a second
blob just a few days after the initial
discovery, and the team eventually
coined the name odd radio circles. At
first, they weren't even sure if these
were real objects or just some kind
[music] of artifact error from the
telescope, but they were able to use
other telescopes to locate the orcs,
confirming that these odd radio circles
were in fact real. The question that
followed was, of course, what are these
things?
Luckily, we've been able to learn a bit
more about orcs since Kapinska first
noticed one.
This is an image of Orc 1 from the Emu
pilot survey, a blurry grayscale blob.
But luckily, the Emu team also produced
this second colorized and enhanced image
that helps to bring out the less obvious
features while still maintaining the
original resolution. In the color image,
Orc1 now appears as a hazy green blue
blob. Because this hazy blob is only
actually visible in radio wavelengths,
the color in this image had to be added
in so that we can visualize it. It also
helps us see more distinct features
within the orc structure
at least a billion lighty years away in
deep space. Initial estimates suggested
that Orc 1 may have a diameter of around
1 million lightyears, but more recently,
observations have indicated that it may
actually be as wide as 2 million
lightyears across. That's 20 times the
width of our own galaxy.
So, we know how big orcs can be and how
distant they are. But what are they?
At first, some thought these strange
rings might be the remnants of a
powerful supernova, but the conditions
were all wrong. For one thing, we
typically find supernova remnants near
the galactic plane, and all of the orcs
we've identified are too far away from
it. Not only that, but it appears that
some of these orcs might have galaxies
in their centers, which is not something
we see with supernova remnants. What's
more, the scale is all wrong, too. Most
supernova remnants are a few dozen light
years across, but these orc rings are
far, far larger, big enough to encompass
entire galaxies at their center. The
orcs we've observed so far are hundreds
of thousands, up to 2 million lightyears
across. These are not supernova
remnants. Orcs must be something else.
Orcs could also be something we are
already familiar with, like the jets
from a radio galaxy. But the vast
distance, or maybe an odd angle, might
obscure our ability to identify them.
Since the initial discovery of OR 1,
astronomers have had the chance to
observe it with additional telescopes,
revealing an object that appears to be
at the center of the circle that can be
seen in both visible and infrared light.
Using the South African MIAT radio
telescope, an array of 64 interlin
receptors, Norris and his team observed
ORC 1 for 10 hours to create an image of
the circle. They overlaid that on
optical data from the dark energy survey
to reveal an elliptical galaxy in the
center of the orc. With this, they were
able to estimate the central galaxy's
[music] distance from Earth at around 5
billion lighty years away. Not only did
they find this central elliptical
galaxy, but the high sensitivity image
also revealed a complex in a structure
of knots and arcs with additional
galaxies found at these knots.
If Norris and his team were correct and
this elliptical galaxy is indeed located
near the center of Orc 1, then it might
have had a hand in creating this radio
circle.
However, it's also possible that the
galaxy's location is a coincidence, as
it may just be near the apparent center
of the orc rather than the actual
center. Armed with this new image and
information, in their 2022 paper, Norris
and his team considered three different
origin stories for the orc, with the
data not favoring one hypothesis over
another.
The first possibility was that ORG 1's
spherical shell was the result of a
cataclysmic event in the elliptical host
galaxy, like the merging of two super
massive black holes, for example. In
this scenario, a merger of two super
massive black holes would send a shock
wave out in all directions, accelerating
electrons in the intergalactic medium.
This could result in a bubble of radio
emissions which could appear to us as a
circle of radio emissions with a
brightened edge or ring. If this were
the case, we would expect the orc to
contain a super massive black hole or an
active galactic nucleus. And not only
does orc one show evidence of a radio
loud galactic nucleus like we would
expect if this hypothesis were correct,
but so do two other observed orcs,
lending further credibility to this
hypothesis.
The second possibility offered by Norris
and his team for OR1's origin was that
it could simply be radio jets from a
radio loud active galactic nucleus or
AGN viewed [music] and on. Radio AGN's
are a type of galaxy that emit large
amounts of energy from its nucleus in
the form of two plasma jets as matter
falls into a super massive black hole at
their center. And as I mentioned, we
already know that AMGs are [music]
present in many of the orgs we have
observed thus far. If we were to view
this kind of system end on where the two
jets were superimposed,
it could create the appearance of what
we see with orc one lobes of radio
emissions superimposed with a host
galaxy at the center.
However, we still need 3D simulations to
help us work out whether or not these
particular AMGs are producing radio
jets, and if so, whether or not we are
viewing them head on. The third and
final hypothesis for an origin story
could be that the radio circle of Orc 1
is caused by what's called a starburst
termination shock. In this explanation,
millions of stars would have been born
during a brief intense period of star
formation in the elliptical host galaxy.
During this time, new stars would have
been born at a rate much higher than
normal and would have lasted for just a
few tens of millions of years, just a
blink on the cosmic time scale. These
stars would emit solar wind that expands
[music] out into space over billions of
years, exciting electrons and creating a
spherical radio emission bubble like
what we see in ORC 1.
While the team modeled this possibility
in more detail than the first two
hypotheses for the formation of Orc one,
showing mathematically how this scenario
was plausible, Norris was clear that the
data did not favor this explanation over
the others. So, while we do have several
promising ideas, the origin of Orc 1 is
still as mysterious as the odd radio
circle itself.
As each new orc has been discovered, the
only thing we seem to know for sure is
that not all orcs are created equally.
After all, the name odd radio circles is
meant as a descriptive name, like an
umbrella term for any odd radio circle
that can't be described by any existing
type of object. So, while all orcs may
include odd radio circles, each
individual orc may have its own unique
origin story, the discovery of orc 2 and
three, the second and third odd radio
circles to be identified, didn't do much
to help solve the mystery of how orcs
are created. In fact, they introduced
even more questions.
Seen in this grayscale image, the two
orcs appear to be very close to each
other. nearly touching. They are roughly
the same size, but on the right side of
the image, ORC 2 is bright and clearly
ring-shaped, while ORC 3, located to the
left, is faint and appears more like a
disc. In fact, Orc 3 may not even be
recognizable in the grayscale emu image
if it weren't for the light gray
speckles seeming to cluster together
into a circular shape right next to the
more distinct ring shape of OR 2.
Now, take a look at this color image of
OR 2 and ORG 3. The diffuse radio
emission has been enhanced in red and
overlaid on top of the original radio
pattern in green. You can see the
obscured green color behind the red glow
where the ring shape of Orc 2 is
located. And to the left, you can see
its fainter sister circle of Orc 3 only
visible in diffuse red.
The proximity of these orcs would
suggest that they are related somehow.
But if that's the case, why do they
appear so different?
As much as I'd like to tell you that
we've solved this curious case of ORG 2
and ORG 3 since their discovery, which
was published in 2021, the nature of
these sister orcs remains an unsolved
mystery to [music] this day.
Before moving on to the theories for ORC
4's origin, I've got to mention ORC 5,
which was discovered in Australian
square km array Pathfinder data in 2021.
While we don't have any leading theories
for ORC 5 specifically, this Orc was
found to have a central elliptical
galaxy like Orcs 1 and four. And
interestingly, Orc 5 was the only one
found to have both this central galaxy
and a nearby neighboring galaxy found at
approximately the same distance from
[music] the Orc ring, which suggests
these two galaxies are likely
interacting gravitationally.
While there may be some repeating
characteristics for every orc we've
confirmed so far, it seems that each one
has their own [music] unique qualities.
Of course, as we discover and confirm
more orcs, it [music] may be that this
won't be the case in the future. But
with so few orcs and so little
observational evidence, it's been
difficult for scientists to nail down
one theory for [music] their origin. And
that brings us to orc 4, dubbed the
cloverleaf orc because of its irregular
shape. Of course, this turned out to be
another unique case. First identified in
archival [music] data from the giant
meterwave radio telescope, the
cloverleaf orc would end up being the
most extensively observed and imaged
[music] odd radio circle to date, having
been observed in radio, x-ray, and
visible wavelengths.
In this stunning image of the cloverleaf
orc, wavelengths from several
observations have been combined with
radio emissions shown in red, optical
wavelengths depicted in white to yellow,
and x-ray emissions in [music] blue.
This orc resides some 600 million
lightyears from Earth, and stretches
[music] more than 325,000
lightyears across, a little more than
three times the width of our galaxy.
In 2024, astronomers at the WM KEK
Observatory in Hawaii detected strong
fluorescent light [music] from oxygen
atoms coming from the cloverleaf orc
stretching across 130,000 lightyears of
the orc's massive structure. [music]
This oxygen 2 nebula of heated
compressed gas, also called shocked gas,
seemed to have been created by a [music]
fastmoving explosion. According to
Allison Coyle, astronomer and
astrophysicist at the University of
California, San Diego, who led the
research team and conducted the study of
orc 4. Since the cloverleaf orc also has
a central [music]
elliptical galaxy, Coyle stated that one
possible explanation was that this orc
could have been formed by a starburst
termination shock event, one of the
three possible hypotheses for [music]
the origin of orc one. The team was able
to calculate the age of the stars inside
the galaxy in the cloverleaf orb and
found that they are 6 billion years old.
Using this and other data, they ran a
simulation that showed how a similar
structure to the cloverleaf orb could
have been created by a starburst event
that caused a high mass outflow rate.
Both the radio emission sphere and this
gas nebula sphere could have been blown
out by the central galaxy by the
shockwave of combined supernova
explosions.
While this is an exciting possibility,
especially because of its similarities
with one of the one hypotheses,
it's not the only possibility.
That same year, using the European Space
Ay's XMM Newton X-ray telescope, a team
led by scientists at the Maxplank
Institute for Extraterrestrial Physics
in Germany detected diffuse X-ray
emissions for the first time in an odd
radio circle coming from the cloverleaf
orc. Based on their observations, the
same team that observed the X-ray
emission led by German astrophysicists
Bulbull and Chang hypothesized that the
cloverleaf orc may be linked to a cosmic
dance between two groups of galaxies.
The X-ray observations suggest that the
cloverleaf orc could be the result of a
messy merger of two galaxy groups that
gravitated towards each other. This type
of a galaxy merger could have created
shock waves that would leave behind a
gigantic bubble of radio emissions like
what we've seen in observations of this
org. However, a lot is still unknown and
it's unclear why this set of galactic
groups would produce such an org. While
other similar galactic group merges
don't seem to leave behind the same
gigantic bubble of radio emissions.
As you can see, the mystery of how orcs
came to be is far from solved. In fact,
it's still up for debate whether the
cloverleaf orc is in fact an orc at all,
seeing as it is more of a diffused cloud
and lacks the telltale bright edges of
radio emissions. Norris points out that
similar clover leafshaped radio clouds
have been observed in other galaxy
groups, not all of which are associated
with orcs. The key to resolving which
objects are part of the orc family and
which are not is more data. Deeper radio
and X-ray observations may be able to
help identify more complex structures
and help differentiate between actual
and near orcs. Luckily, several other
candidate orcs have been identified and
they may offer additional data for
astronomers to study and compare to the
already known cases.
Now, instead of WTF, the side note on
these strange radio emissions has a
proper name, orcs.
But even though the jury is still out on
how orcs came to be, we are constantly
gaining new insights from the likes of
Project Emu and ASCAP. [music]
While studying emu data from a nearby
dwarf galaxy called the small melanic
cloud, astronomers spotted the ghostly
remains of two supernova remnants that
were previously unknown to science,
adding to our catalog of celestial
[music] objects. In addition to those,
another nearby supernova remnant was
found by using the emu survey in 2023
and turned out to be one of the closest
supernova remnants to our Earth at just
4,200 lighty years away. This supernova
remnant known as this was found to be
about 130 lighty years across and is
thought to be just 13,000 years old.
Not only has Emu aided in the discovery
of previously unknown supernova remains,
it is also paving the way for using
machine learning and the power of
citizen science to identify and catalog
some 4 million radio sources which could
include orcs as part of a project called
the radio galaxy zoo emu or RGZ emu. As
of 2025, the project has had more than
2,000 volunteers and has helped to
classify more than 92,000 sources. But
the coolest part, you can join in and be
part of the Citizen Science Project
yourself. To learn more, visit
zuniverse.org and search for the radio
galaxy zoo emu project.
As our tools continue to improve, I
believe that astronomers are bound to
discover more orcs and even more objects
we don't know even exist yet, we may
learn not just how these radio rings
formed, but we could also learn more
about the life cycles of galaxies, the
effects of starburst events, and how we
may be able to trace gas from ancient
events far outside their galaxy of
origin. For now though, the mystery of
the origin of these odd radio circles
persists, although with several
promising hypotheses. And to unravel
this mystery, astronomers will have to
conduct cosmic archaeology on a scale
almost too big to fathom.
In 2022, astronomers using the Merchesen
wide field array discovered a strange
new radio signal that was arriving every
22 minutes.
The astronomers were no strangers to
such repeating signals. They typically
come from pulsars, neutron stars, which
send [music] intense pulses of light
across the universe as they rotate on
their axis.
But as they began to look deeper into
records of past observations, they
realized this signal had been arriving
at Earth since at least 1988 with
remarkable stability, far more stable
than is expected for a pulsar rotating
every 22 minutes.
If it was a neutron star, it was unlike
any they had seen before. So, where was
this signal coming from?
I'm Alex Mccoan and you're watching
Astramm. Join me today as we grapple
with the mystery that lies behind this
signal, which will challenge our
understanding of some of the most awe
inspiring objects in our cosmos.
The location of the source named
GPMJ1839-10
is roughly 18,000 lighty years away. Its
signal arrives as pulses that can last
any amount of time between 30 seconds
and 5 minutes. These pulses can appear
at any time in a window of just over 6
1/2 minutes, which is centered on 22
minutes after the previous pulse. To us,
this may seem like a great deal of
variation. 30 seconds and 5 minutes are
very different durations, and the pulse
arrival varying by over 6 minutes
doesn't [music] paint a picture of a
very stable source. But neutron star
dynamics can be very complicated. And if
the source is indeed a neutron star,
then many factors can affect the
duration and arrival [music] times of
the pulses that we receive.
Nevertheless, the astronomers were able
to spot this signal hiding in data from
the last 35 years and used this expanded
data set to average out the
fluctuations.
They calculated that the source was
rotating once every 21 minutes and 58
seconds, as well as how much it had
slowed down. But to their surprise, they
calculated that this rotation period
remained unchanged over the past 35
years. Even though it is expected that
the source will slow down as it radiates
energy into space,
we can only say for sure that if the
source has slowed down, its rotation
period would not have increased by more
than 0.28
milliseconds over the 35- year period.
because otherwise we would [music] have
been able to detect this in our data.
This is an absolutely minuscule amount
and it shows that whatever the object is
is spinning with remarkable stability.
This usually isn't odd for a pulsar.
These are the timekeepers of the
universe, the clocks of the cosmos,
mechanistically ticking away with such
certainty that we can use them to
measure time across vast stretches of
the universe. However, this level of
stability is odd for a pulsar that is
rotating so slowly.
To understand what makes it odd, we need
to recap how pulsars work and what makes
them slow down over time.
Pulsars are neutron stars, the leftover
cores of dead super giant stars, which
barring black holes, are the densest
objects in the universe. Planets like
our own are made up of atoms which
consist of over 99.999%
empty space due to the vast separation
between the electrons and the incredibly
dense nucleus they are whizzing around.
But imagine an entire star made purely
out of the neutrons that are found in
the nucleus. No electrons, no protons,
no empty space.
merely a teaspoon of it would have as
much mass as 11 times that of the entire
human population, all 8 billion people.
A typical neutron star is around 35%
more massive than our sun and squeezed
into a sphere that has the diameter
about as long as the island of
Manhattan. To call it dense would be an
understatement.
For reasons still unknown to
astrophysicists, the extreme environment
gives rise to an incredibly strong
magnetic field. What does this have to
[music] do with the signals we receive
from pulsars? Where do the light waves
come from? To answer this question, we
need to understand a complicated process
that gives rise to the signal. An
exponentially growing shower of light
and matter, all spawning from a single
electron.
Near the magnetic poles of a neutron
star, an electron can be accelerated by
the magnetic field and emit a so-called
curvature photon tangential to the
magnetic field line. This marks if you
like the start of a pulse. The curvature
photon moves in a straight line until
the [music] angle between its momentum
and the magnetic field line becomes too
great. Once this angle reaches a
threshold, the light dissipates and
imbuss its energy into the quantum field
of electrons. An electron is created
alongside its antiparticle, the
positron.
The electron posetron pair has some
momentum perpendicular to the magnetic
field lines which they spontaneously
dispose of in the form of synretron
photons.
These two synretron photons can each
then produce another electron positron
pair after they reach the threshold
angle between their momentum and the
magnetic field lines.
This process repeats again and again,
exponentially increasing the amount of
photons and electron positron pairs
created until the synrotron photons no
longer have enough energy to create
electron positron pairs, putting an end
to the cascade.
These photons then beam out into space
while the original electron continues
its journey generating more curvature
photons and more cascades as it moves
along the magnetic field lines.
This pair production cascade is why the
light of a pulsar is so intense that we
can detect a signal from this tiny
stellar remnant thousands of light years
away.
But why do we see this light as pulses
rather than a continuously glowing
beacon of light shining at us? This is
because the magnetic poles of a neutron
star are rarely ever aligned with its
axis of rotation.
Just like on Earth, the magnetic north
pole that our compasses point to isn't
the actual geographic north pole the
Earth rotates around. So, the pulsars
are like great lighouses sweeping their
beams of light around the cosmos as they
spin. And for an observer far away, like
us on planet Earth, we see the beams
sweep past us again and again as the
pulsar completes its rotation on its
axis. These are the pulses of light that
our telescopes can detect.
However, this is light with very long
wavelengths in the radio part of the
spectrum. Meaning only a radio telescope
can detect it. The light that the
cascade produced is of the same
wavelength with the peaks and troughs of
the light waves fluctuating in unison.
The light waves are also polarized which
means they are all aligned along the
same axis. This is a hallmark of neutron
stars and this is precisely what we
observe in the 22minut signal. The
signal also has fluctuations that last
between 0.2 to 4 seconds where the axis
of the light's polarization suddenly
changes by 90° perpendicular to the
original axis and then back again. This
effect is yet another signature of the
cascades at the poles of the pulsars.
So much of our data points to a pulsar
being the signal that you'd think this
was an open andsh shut case. But one
variable that we've mentioned earlier
throws this entire theory into doubt.
The slow rotation rate of the neutron
star or rather the combination of the
slow rotation rate and the high
stability of the rotation rate of the
source.
You see, as pulsars lose energy by
shining their powerful beams into the
cosmos, [music] conservation of energy
will ensure that the pulsar slows down.
Eventually, the pulsar will slow down so
much [music] that it can no longer power
the pair production cascades and the
light emission starts to shut off. The
pulsar has entered the so-called Death
Valley.
This graph plots neutron stars based on
their rotation period on the x-axis and
the rate of change of their rotation
period on the yaxis.
Death Valley is shown in this gray band
running through the middle. And any
pulsar that has properties below this
line should not be shining as the bright
lighouses they usually are.
We see that our signal is below even the
lowest line marking the death valley.
meaning that if it were a pulsar,
[music] it should be well and truly
switched off. And yet, we are detecting
it. Look at the cluster of other known
neutron stars on this graph. They
usually spin between 10 times a second
to once every second. In comparison,
[music]
our signal has a spin rate of once every
1,318
seconds, over a thousand times slower
than the typical pulsar.
This would be fine if it was also
slowing down quickly, which equates to
moving this data point upwards on this
graph above the Death Valley. Such rapid
energy loss would power the pair
production cascade necessary to light
the beacon of the neutron star. Yet, the
neutron star is mindbogglingly stable,
and it makes no sense that we can detect
it. The astronomers who found the signal
considered an alternative mechanism that
might explain how a neutron star with
such properties might have produced this
light. Maybe the neutron star is a
magnetar, a neutron star that has an
unusually strong magnetic field, greater
than 10,000 times the strength of the
weakest neutron star magnetic fields.
Magnetars are known to undergo star
quakes, cataclysmic events that release
the tension in the upper crust of a
neutron star. These stresses are
produced by the [music] strong magnetic
fields of the magnetar as well as the
slowing down of the magnetar rotation. A
fast spinning magnetar will bulge in the
middle due to the central fugal force
distorting the star from a perfect
sphere. As the magnetar slows down, the
outer layers need to readjust to a new
equilibrium and lose some of the bulge
they have. The crust snaps into a new
position, causing magnetic fields to
temporarily realign and powering the
release of the energy as light that we
can detect on Earth.
The most powerful star quake detected,
that of SG1806-20
in 2004, released so much energy that if
it had taken place as far away as 10
light years from Earth, it would have
caused a mass extinction event. If
something is able to light the beacon of
a dead pulsar, it would be this. So,
could GPMJ1839-10
be a magnetar that has undergone a star
quake? Have we resolved the mystery of
the 22-minute signal? It seems not. We
expect these star quakes to also emit
light in the X-ray part of the spectrum.
Yet, no X-rays can be detected from the
position of the source roughly 18,000
lighty years away.
It also wouldn't make sense for a
magnetar outburst to be going on for
three decades. The star quake is a
temporary phenomenon and the energy
dissipates within a few years at most.
It is simply incomprehensible that this
signal would have existed for 35 years
if it was indeed a magnetar.
Once again, the unique properties of our
signal exclude it from being a neutron
star, even an unusually powerful one
that has undergone a special event, such
as a star quake. But what else could the
source of this mysterious signal
possibly be? The astronomers who
discovered the signal proposed a few
alternatives for the identity of the
source. One possibility is a highly
magnetic white dwarf. A white dwarf is
another type of remnant left from the
recent death of a star, but one that
didn't have enough mass to collapse the
empty space in the atoms to [music]
become a neutron star. A remnant that
has an unusually strong magnetic field
could produce radio emissions. And as it
is not a neutron star, it could get away
with being as slow and stably rotating
as the source of our object while doing
so.
The issue is this would require an
exceptionally strong magnetic field
greater than any we have spotted on a
white dwarf. A sco is the only known
radio pulsar that is actually a white
dwarf and its radio emissions are a
thousand times less luminous than the
source of our 22-minute signal.
So [music] if a white dwarf is unlikely,
what are our other options?
Astronomers have observed low frequency
radio waves coming from the interactions
between stars and exoplanets as well as
a binary of two brown dwarfs rotating
around each other. But this emission is
typically weaker, around 100 million
times weaker than the source of our
signal. In the end, it seems like none
of our theories can explain the 22minut
signal. While the unresolved question
about the source of the signal may feel
frustrating, this is precisely the kind
of mystery that astrophysicists look
for. When scientists find new data that
challenges our long-held theories, they
can usher in revolutions in our
understanding of the universe around us.
Here, our already shaky understanding of
neutron stars is being challenged. The
astronomers are confident that the ease
with which they identified this signal
means similar sources lie out there in
the galactic plane waiting to be
identified. Just like GPMJ1839-10,
the other signals might already be
lurking in the data we have collected.
Identifying more of these signals will
shed light on the process powering
emission beyond the neutron star Death
Valley. Whatever lies behind the
22-minute signal, we are sure to learn
of an entirely new phenomenon that we
have never seen before. Isn't that
exciting?
What do you think could be the source of
the 22-minute signal? Let me know in the
comments below.
In the Milky Way alone, there are
thought to be 100 billion planets.
Of these, 30 million are thought to
exist in Goldilock zones that are just
the right distance away from their suns
to support life, while also containing
the right mix of chemical elements that
life like ours can arise from.
In all the 13 billion years of the
universe's existence, if just a tiny
fraction, if just 1% of these went on to
become civilizations capable of reaching
out into the cosmos, then we should be
seeing signs of thousands, if not
millions of alien races running across
our galaxy.
And so in the words of Nobel
Prizewinning physicist Enrico Fermy in
his famous Fermy paradox, where is
everyone?
I'm Alex Mccoan and you're watching
Astramm. Today we will be exploring some
of the possible answers to this question
because although we don't know for
certain whether aliens exist, there are
actually some surprising barriers that
might stop us from seeing them even if
they do.
Let's start by addressing the elephant
in the room. Maybe there's no one to
see.
In our last video, we explored the
possible odds of alien life existing and
found that if it was true that it's
quite difficult for life to arise from
non-living materials, or if it's
unlikely that life would go on to become
intelligent as we have done, then it's
entirely possible that there would be no
ships or signals in the sky simply
because there are no aliens. We would be
the first ones to ever make it this far.
All other planets could be empty and
desolate.
It would then be our opportunity to
spread out across the universe and
discover all these empty rocks. And the
only life we'd ever encounter is
whatever we brought with us from Earth.
While this is a perfectly reasonable
possibility, there is no conclusive
evidence to prove [music] it wrong. This
is not the only explanation that exists
for why the sky isn't full of signals.
We should also be aware that we are
constrained by a surprising natural
limitation.
For us to discover or make contact with
an alien civilization, one of two things
needs to happen.
Either we need to send out a message to
an alien civilization and then have them
send a message back to us or the alien
civilization needs to have made the
first overture messaging us directly.
There are different ways of doing this.
For instance, we might be sending
spaceships to each other or we may be
using unmanned probes. But there are
significant issues with doing anything
other than sending messages. Sending a
spaceship is a tricky business. At the
current speeds our spaceships are
capable of, it will take potentially
millions of years for an astronaut to
reach their destination. The Voyager 2
probe took about 49 years to even leave
our heliosphere.
The nearest star is 4 light years away.
In other words, it would take over
81,000 years to get even there, or about
2,700 human generations. [music] And
that's assuming that we have aliens as
our closest nextoor neighbors.
Even if we make allowances for
technology to improve, it takes colossal
energy to accelerate an object up to
light speeds. Actually, it would take
more energy than exists in the universe
for reasons we won't get into here.
mass just does not like to travel at
those speeds.
So unless we or our alien friends are
able to come up with some kind of
workaround, most likely the easiest way
to communicate with other civilizations
is to send them radio signals.
In fairness, it's not implausible that
this speed cap will one day be broken.
Scientists have hypothesized some
promising things involving moving the
space around you in war bubbles rather
than by moving yourself directly. The
speed of light limit only applies to
movement within a local area. So if it's
your local area that's moving, you're
fine. We actually have examples of this
in nature around black holes, which I
explore in one of my other videos.
But until that becomes a scientific
reality, let's just go with the fact
that it's much easier to call than to
visit in person. It's significantly
easier and cheaper to send out light or
radio waves. As simple as turning on a
sufficiently large light bulb. So let's
assume that this is how our first
contact with aliens will occur.
Even here, however, we hit a roadblock.
Radio signals and light are more than
capable of traveling at relativistic
speeds. It's called the speed of light
for a reason, after all. However, that's
its limit, light speed. Just less than
300 million m/s.
No signal can go faster than that. And
this in turn limits how far we are able
to see [music] through space. Any signal
from us would need to travel out across
space before reaching alien life. And
then even if they decide to respond
immediately, their response would need
to travel all the way back if they
decided to respond. Let's imagine that
happens though. We only invented the
radio in the mid 1890s, so we have not
really been able to do this for very
long. As such, we would only be able to
exchange a message with aliens who lived
at most 60 light years away from us. 60
years for a signal sent out in 1900 to
reach the alien civilization and 60
years for it to come back.
Our galaxy is roughly 100,000 lighty
years across. So, the 60-year light
bubble we have, we could have
communicated with is truly tiny.
In fairness, this limitation goes away
if the aliens contact us first. After
all, we are now receiving light in the
James Webb telescope that has been
traveling for 13 billion years, from
nearly the beginning of the universe. If
an alien civilization came into being
around 2 billion years ago, and they've
kept [music] existing since then, that
means they now have a 2 billion
light-year bubble from which we could
technically see them. A 10
billionyear-old civilization now has a
10 billion light-year bubble. But if
they were 10 billion lighty years away
and only 9 billion years old, they would
be completely invisible to us.
Assuming that such faraway aliens exist,
why aren't we seeing any of them? Where
are their signals?
Well, this line of thought may rest on a
faulty assumption that there haven't
been any signals coming in from the
stars. There have been signals. We're
just not sure what they are. Let's
explore this with a fascinating example.
In 1961, in their pursuit of evidence
for the existence of alien life, which
is worth noting because it opens up the
possibility of confirmation bias,
researchers at the Ohio State University
finished work on a specialized telescope
called Big Ear. It was the size of three
football pitches and worked on a similar
basis to modern-day telescopes in that
it captured signals using its large
mirror on one end [music] and bounce
them through smaller mirrors on the
other into two receivers in the center
where the results were then processed.
You may notice that these capture dishes
are just wireframes though, not true
mirrors. This is because Big Ear was a
radio telescope. It wasn't trying to see
with visible light.
The way Big Ear worked meant that it was
more limited in its motion than a
telescope that could rotate in any
direction. Big Ear could only tilt its
primary reflector up and down, which
meant that it was somewhat limited to
only listening to a point in a narrow
strip of space at any one time. This was
cheaper and easier to design. And the
designers had an idea that would let
them get around Big Ear's limitations.
They built Big Ear at just the right
orientation so that the rotation of the
planet would be what turned it left and
right. With the Earth turning it one way
and with its tiltable reflector
adjusting it along the other axis, you
could point Big Ear towards any point in
the sky if you have enough patience.
Quite a clever solution.
Big Ear's direction of attention would
sweep around the night sky in large
circular arcs, listening out to try to
spot any unusual signals that we did not
have a natural explanation for. And sure
enough, in 1977,
Big E found something. On the 15th of
August, a 72 second long pulse of radio
waves came in that were 30 times more
powerful than anything Big Ear had heard
before in the background chatter of the
universe.
It was so out of the ordinary that the
researcher who found it wrote wow on the
computer printout when they saw it,
giving it the historical name of the WOW
signal. It was incredibly uniform. It
rose in intensity, peaked, and then
dropped back down in a smooth motion
instead of the erratic fluctuations you
might have expected from cosmic
radiation.
This indicated that whatever had made
the sound was broadcasting consistently,
kind of like the beam of a lighthouse
sweeping out across the stars with us
turning to look at it and then turning
away again. Except it wasn't consistent.
Due to Big Ear's design, researchers had
to wait a few minutes before the second
ear of Big Ear moved to look at that
particular patch of space the WOW signal
had come from. And when they got there,
the signal had vanished.
Ever since then, despite checking back
in from time to time, we have never
heard another WOW signal come from that
region of space to this day.
So, what was it? A fault in the
machinery of Big Ear, a passing comet
that threw out a momentary burst of
signals, or an alien civilization trying
to communicate?
The fact of the matter is, we don't
know. It's possible that the WOW signal
has a perfectly natural explanation.
After all, when the regular consistent
pulses of X-rays from pulsars were first
discovered, some people thought that
they were aliens trying to communicate
before the real explanation was found.
Maybe we will one day find another WOW
signal and we'll see that it was nothing
alien in origin at all. But there's
[music] a technical point that needs to
be made here.
If I were the scientist in charge, I
would point my telescope at the point in
the sky that the WOW signal came from
and would wait to see if anything else
came from there. If I didn't, another
signal might come in and I'd miss it.
But consider the way Big Ear was
constructed. It rotates only within the
rotation of the Earth. It physically
can't stay looking at the same place for
more than a few moments. As such, we
have no idea whether more signals came
in from that region of space or not.
Hundreds could have come in over the
next several hours, including an entire
orchestra performance. But as Big Ear
wasn't listening in that direction for
more than a moment in the day, it would
have only heard a single note.
This highlights a conscious decision on
the part of organizations like SETI who
are seeking intelligent life in the
universe. Because resources are limited
and space is vast, they lack the time
and funding to take a telescope and
point it for potentially decades on end
at a single place just to see if aliens
want to talk to us again from that spot.
Instead, they favor broad sweeps of
space to cover as much ground as
possible, hoping to get a lucky hit. If
they were fishing, rather than leaving
their line in the water at a single
point, they are casting and casting,
seeing if anything bites immediately and
moving on if nothing does. This approach
is more reasonable than my analogy makes
it sound, as aliens are not fish to be
attracted to a lure or scared off by a
splash of a telescope looking at them.
And although the first process is more
methodical, there's every chance that if
you just sweep your telescope across the
sky, you will encounter some evidence or
signal. The problem comes with the
follow-up. There have actually been
numerous signals like the WOW signal
that radio telescopes have picked up
over the years. Strange and unusual
bursts that we have no current
explanation for. But because we aren't
focusing on them and thoroughly
following up over years of continued
dedicated study, we are missing a lot of
information. And as a result, we end up
with weaker conclusions,
which brings us to our conclusion.
Perhaps we are seeing no aliens simply
because of our method. Of course, these
are just a few of many possible
theories. For this video, I've tried to
focus on some of the technical
limitations to finding signs of alien
life. However, there are other more
theory based explanations that lean more
on speculation. They are fascinating,
though, and give us interesting insights
into our own civilization. So, if you've
enjoyed this subject, then I'll go into
them in another video. Do you think
there are aliens up in the night sky? If
so, why do you think they've not spoken
to us? Be sure to leave your ideas in
the comments below.
The search for alien life is a difficult
one. How would we know that aliens
exist? An obvious answer would be if
they visited our planet on mass. If,
like in the film Independence Day, their
sources floated above every city in the
world. Or perhaps if their envoys met
with us, shaking hands with our world
leaders while cameras broadcasted the
moment on national television. or maybe
if they started trading with us and
their inventions and resources began
appearing in our everyday life.
There is fortunately or unfortunately
not much evidence that this has ever
happened. But while visits from aliens
would certainly be preferable, that's
not the only possible way aliens could
prove their existence to us. It's much
more plausible that they would do so
with their signals.
We've spent a lot of time on this
channel discussing some of the reasons
why aliens might not have talked to us.
But on the flip side, what are the
strongest pieces of evidence that they
have already done so? Which signals are
considered the best candidate so far for
a message from an alien civilization?
I'm Alex Mccoan and you're watching
Astramm. And rather than explain why we
haven't heard from aliens today, let's
look at where perhaps we already have.
Obviously, when it comes to alien
signals, there is some ambiguity as to
what exactly we are looking for. Aliens
are, after all, alien. We are not quite
sure what to expect from them as they
will have likely evolved in conditions
different to our own and may well have
cultural outlooks that make perfect
sense to them but are completely obscure
to us. Their definition of a good way to
say hello to the universe might be very
different from ours. Researchers looking
into possible signals from other planets
have to remain very open-minded about
what an extraterrestrial signal might
look like. But that means such signals
can get confused with signals from
natural sources that we simply do not
understand yet. How can we tell the
difference?
Let's look at a few examples to show you
what I mean. In 2019, as part of the
breakthrough listen initiative, the
park's Marang telescope in Australia was
observing Proxima Centuri, the star
nearest to our own. It was recording
data to learn more about stellar flares.
But when SETI researchers, a collective
term for the search for extraterrestrial
life, went over the data it had
collected sometime later, they found
something unusual. A signal which later
came to be known as BLC1.
Could the star closest to our own
actually harbor advanced alien life?
The signal was fascinating as it could
not easily be explained away by
conventional sources. It lasted for
several hours, which is longer than the
time it normally takes a human satellite
to pass by overhead. It had signal
drift. [music] Its frequency was
shifting, which implied possible
movement relative to the telescope, so
it likely wasn't coming from a
stationary object creating interference
on Earth.
One of the most compelling things it had
going for it was its thin narrowband
signal. In nature, radio waves are never
so narrow in their range. They always
fluctuate. Unless there exists some
natural source out there we've not
discovered yet. The only thing that
produces such a concise signal as this
is technology, either human or alien.
when no obvious explanations for
existence could be found amongst human
sources. Naturally, scientists wondered,
could this be the signal from alien life
they had been looking for?
Along with the WOW signal, which we
looked at in a previous video, [music]
BLC1 is one of the strongest candidates
for signals that may have been created
by alien civilizations.
And yet, even this signal has its
drawbacks. [music]
Scientists could not link it to any
sources of obvious interference from
technology on Earth. But on closer
examination of the data, it did match
other radio wave signatures that came up
on other days of the search. Except
these other signals occurred no matter
what direction the telescope was
pointing in. Neither were they able to
detect BLC1, the signal from Proxima
Centuri with later observations.
>> [music]
>> So, while they don't know exactly what
interfered with the telescope to produce
BLC1, the odds of it being interference
are nonetheless quite high.
Let's take a look at another candidate,
the somewhat mouthier SHGB02
+14A.
When one of the first SETI experiments,
Project OSMA was started in 1960 by
Frank Drake, it began on the basis that
if alien life were to communicate with
the rest of the universe, they would do
so at frequency 1420 MGHertz. The logic
behind this was that this was the
frequency emitted commonly by hydrogen,
one of the most widespread elements in
the universe. Aliens looking to
establish communication with other
civilizations might use such a frequency
as a sort of common ground, a wavelength
that probably holds a special
significance to any race.
This might have been a leap of logic,
but it certainly made SHGB02
+14A of interest later because this
signal, let's just call it SHG for the
rest of the video for the lack of a
punchier name, did indeed broadcast at
this exact wavelength.
SHG was spotted on three separate
occasions in 2003 using the Arosibo
telescope and the computational power of
5.2 2 million home computers as part of
the SETI at home initiative. A rather
cool program that is sadly no longer
running. SHG had no obvious explanation
for his origins in nature and it didn't
appear to be interference,
but it was also too weak to say for sure
whether it was clearly technological or
not. On top of that, its location was
peculiar. It came from a spot devoid of
stars up to 1,000 lighty years away from
Earth. And although it experienced
drift, it did so in a manner that made
scientists suspicious.
If a signal originates from a planet,
then there are a few things we might
reasonably infer. A signal being
broadcast from a planet either on the
surface or in orbit just above it would
likely experience some Doppler shift as
it alternated from moving away from us
to coming towards us through the
circular path it was taking in space.
There would also be movements where it
dropped out of view entirely as it moved
behind the planet. While SHG did indeed
experience fluctuation in its signal
frequency, ranging from 8 to 37 hertz
per second, this would only come from a
planet that was rotating 40 times faster
than Earth, which seemed high. It was
also strange that each time the signal
was spotted again, no matter where it
had been when it had last been cited, it
always began at 1420 MHz.
The odds of you looking at an orbiting
transmitter on three separate occasions
and each time spotting it starting off
at the exact same location is incredibly
slim, which is what you'd need for this
to make sense. This observation pointed
to it being more likely SHG was some
kind of glitch in the technology.
By looking at the process by which the
BLC1 or the SHG signals were evaluated,
we gain an interesting insight into how
SETI determines whether something might
be of alien origin.
To me, it is a method that lines up best
with this quote from Sir Arthur Conan
Doyle in the words of his famous
detective Sherlock Holmes. When you have
eliminated the impossible, whatever
remains, [music] however improbable,
must be the truth.
Each time researchers came across a new
signal, they began by eliminating all
possible alternatives. Could it be
interference from a passing satellite?
[music] Is there anything in nature that
we know of that could be producing this
effect? Can we in any other way explain
why this signal is here and behaving the
way that it does? So far, alternative
explanations have been found for these
contenders for alien communication.
Even on the occasions where human
interference can be ruled out entirely,
that still leaves open the possibility
that these mysterious signals might just
be undiscovered natural phenomena. And
that is precisely the current discussion
around the last candidate for alien
signals I'd like to leave you with
today, fast radio bursts.
If an alien civilization were ever to be
detected, it might not be intentional on
their part. powerful engines activating
or beams firing all might release bursts
of energy that give away a galactic
civilization which makes fast radio
bursts orrbs
interesting.
They are just as the name suggests very
fast bursts of radio waves. We have
detected hundreds of these strange
millisecond long bursts across the sky.
Scientists theorize that there might be
thousands of them occurring every single
day. They have mostly been detected
outside our galaxy, but one was detected
within the Milky Way in 2020, so they're
not completely foreign to us. They seem
to be coming from extremely powerful
magnetic fields. And as of yet,
scientists have no clear idea about what
their origin might be. There are plenty
of theories. Perhaps they are emitted by
neutron stars or maybe black holes, but
there is no proof that puts any one
theory over another, including that of
alien technology.
The Chime telescope in Canada has a
unique design that makes it ideal for
detecting these fleeting blips in the
cosmos. Avoiding the pitfall of other
telescopes, rather than pointing at any
one point in the space, Chime's multiple
cylindrical parabolic reflectors are
able to draw data from an entire swath
of the sky at the same time. It began
detecting in 2018 and is still going
strong to this day. It has detected FRBs
that are repeating as well as one that
is definitely associated with a magnetar
star. Perhaps allrbs can be associated
with such stars. Perhaps not. But that
is just the point. Perhaps one day we
will be able to identify the origin of
allrbs and we'll know that they have a
perfectly natural origin.
Perhaps the search for alien life will
have to begin a fresh. But there is
always that tantalizing hope, that slim
possibility that one day a scientist
rule out signal after signal that
finally one will come in that defies
alternative explanation.
If all other explanations can be ruled
out, we can say for certain that no
natural source caused this. Then in the
words of that great detective, we will
have no choice but to accept the
improbable.
So, these are some of the best
candidates for signals from another
planet, but even they come with massive
strikes against them. We have not yet
found a signal that conclusively points
to the existence of aliens. But that is
not to say that we never will. It's
never aliens, right up until the moment
where it is.
800 light years away, there's an unseen
antimatter factory churning out high
energy posetrons.
Tiny particles of antimatter that are
streaming through the cosmos and
colliding with our planet.
For much of history, we didn't know this
strange source existed. Most of the
positrons bombarding us went completely
undetected, instead getting absorbed in
our planet's atmosphere. It wasn't until
we started looking from beyond the
bounds of our planet that we noticed
them. In 2011, NASA's Alpha Magnetic
Spectrometer, a state-of-the-art
particle detector some 200 m up aboard
the International Space Station, was
switched on. What did it find? You
guessed it, posetrons.
The presence of these subatomic
particles was to be expected, but not in
the numbers they were finding.
Such was the sheer volume of posetrons
being detected that the usual sources
like natural radioactive decay and
cosmic rays no longer offered a
sufficient explanation.
So where were they coming from?
We've only recently been able [music] to
trace the culprit of this cosmic
antimatter shower. And it all comes down
to another high energy discovery. a
strange gammaray haze named gaminga
first identified in the 1970s.
What is this mysterious source of gamma
radiation and what does it have to do
with the unusual abundance of high
energy posetrons hitting our planet?
I'm Alex Mccoen and you're watching
Astramm. Join me today as we tune into
the enigmatic frequency of Gaminga whose
gamma radiation has lit up the world of
astrophysics for decades.
Up in our night sky, nestled in the
Gemini constellation in the northern
celestial hemisphere, there is something
peculiar going on. In 1972, NASA's small
astronomy satellite 2 or SAS2 identified
an unknown source of gamma radiation.
But with the technology available at the
time, the best it could do was trace its
origin to this wider region of our Milky
Way. So, the radiation's ultimate source
remained hidden among the stars for
decades. Nevertheless, it was given a
name, Gaminga, as coined in 1976 by
Italian physicist Giovani Binyami, who
would dedicate his career to studying
it. It's a play on words, a combination
of Gemini, the region where it's
located, and gamma, the type of
radiation it emits. Gaminga is also a
pun in Bingyami's Milan dialect, meaning
it's not there. A fitting name for a
gamma ray haze with unknown origin.
It wasn't until 1983 when Binyami and
his team finally had their big break.
They managed to identify a weak X-ray
signal from Gaminga using the Einstein
X-ray satellite. This meant although its
exact position remained unknown, they
could narrow down their search area and
were getting closer to uncovering
Gaminga's hiding place. But it didn't
answer the big question, what is it? As
astronomers could still only offer vague
guesses about the true nature of the
source.
That was until 1991 when they had
another lucky break. Two separate
missions identified radiation coming
from Gaminga, and they weren't constant
signals, but pulses. The first of these
discoveries was made with a Germanbuilt
X-ray telescope known as Rosat, short
for Rken Satellite, named after the
German word for X-rays. Rosat was the
first to identify pulses in the X-ray
signal coming from Gaminga and soon
after they were also confirmed in the
gamma wavelengths by the energetic
gammaray experiment telescope or egret a
telescope aboard NASA's Compton Gammaray
Observatory satellite
not only did these complimentary
observations demonstrate that the X-rays
and the gamma rays were both coming from
Gaminga but for the first time they
revealed what Gaminga was with a period
of 0.237
seconds flashing as it spins around its
axis a little more than four hertz or
four times per second. Gaminga behaved
like a pulsar.
A pulsar is a type of neutron star that
spins rapidly, emitting beams of
radiation that sweep across space like a
cosmic lighthouse. From across the
galaxy, most pulsars appear to flash in
radio waves anywhere from a few times a
minute to as fast as 700 times per
second. And at this point in the early
'90s, they were incredibly rare. You
see, before Rosat and Egret, only two
other high energy gammaray pulsars had
ever been identified. The Crab and Vela
pulsars. And Crab and Vela were
different to Kaminga [music]
in a couple of key ways. First, in
addition to gamma rays, both of these
pulsars also produced radio waves and
were therefore visible using radio
telescopes. So if Kaminga was a pulsar,
then it would be the first discovery of
one that was apparently radio silent
only emitting enough radiation to be
seen in the gamma and X-ray wavelengths.
And second, Crab and Veil were
surrounded by their respective nebula,
remnants from when they were created
from supernova explosions.
But Ginga's nebula was conspicuous by
its absence.
So why is Gaminga, this powerful source
of gamma rays, so good at hiding from
our radio telescopes? Where is its
nebula? Or could it be a different type
of object altogether?
Well, the answer to the first question
is in part because we hadn't been
listening properly due to the
limitations of the available technology
and due to our understanding of the
radio emissions of such stellar
remnants. You see, while radio pulsars
can emit radio waves across a wide
bandwidth from as low as 17 MHz to above
87 GHz, around half the radio spectrum.
Not all of these frequencies travel well
through space. Even though we've known
since the 1970s that radio pulsars often
peak between 100 to 200 meghertz where
they are intrinsically brightest, things
like the interstellar medium, background
sky temperature and effects from the
ionosphere mean that lower frequencies
are dampened as they make their way
across space, resulting in very weak
signals that are much more difficult to
detect.
Because those radio signals are so weak,
most radio telescopes hadn't been
looking for them. Instead, confining
themselves to searching for signals
between 430 and 1,600 MGHertz.
This would have been fine had gaming
behaved as expected for one of its kind.
Since it did not, it took until 1997 for
scientists to realize what was
happening. Three independent
observations from the Pusheena Radio
Astronomy Observatory were able to
identify extremely weak pulses from
Gaminga using a sensitive transit
antenna. The faint radio pulses came in
around 100 MHz, which explains why
previous radio searches for Gaminga had
come up silent. Turns out Gaminga wasn't
truly hiding and had been sending us
signals. We just weren't listening
correctly.
That same year, a team led by the late
astronomer Yanush Gil theorized that
another reason Gaminga had appeared to
be radio silent may be its magnetic
field. Models showed that radio waves
may be absorbed or refracted within the
pulsar's magnetosphere, leaving only
weak pulses around [music] 100 megahertz
to be detectable. This would effectively
leave it quiet at the higher radio bands
than most telescopes used.
Confirming Gaminga was a pulsar and
specifically a gammaray pulsar was a big
deal. In fact, 99% of its output is in
the gamma range, making it one of the
brightest gamma ray sources in our
entire galaxy.
It is, as it turns out, all that's left
after a star several times more massive
than our sun exploded about 350,000
years ago.
But its relative radio silence and its
apparent lack of a nebula weren't the
only unusual things about this pulsar.
When Italian astrophysicists, including
Bingyami, Gaminga's name giver, compared
a series of observations from the
European Southern Observatory's 3.6 6 m
telescope and new technology telescope
with observations from the Canada France
Hawaii telescope. They found that
Gaminga was moving. Not only that, it
was traveling at an unusually high speed
of around 0.2 arcseconds per year. As a
reminder, an arcsec is a very small unit
of angular measurement used when we need
more precise measurements than a degree
would allow. Within each arc degree,
there are 60 ark minutes. And within
each ark minute are 60 ark seconds.
These ark seconds are a common unit used
in astronomy to talk about the movement
of objects across the sky from our
perspective on Earth.
If you were to draw a circle around the
orbit of the moon around the Earth,
there would be 360°
around that circular path. So, at any
given time of day or night, assuming
nothing is blocking your view of the
horizon, you can see about 180° of the
sky. And from the horizon to the zenith,
the top of the sky is 90°.
If you hold out your little finger at
arms length and close one eye, the tip
of your little finger covers about one
degree of the sky roughly. Next time
you're outside on a clear night, try
this and see if your little finger can
cover the moon. It should because the
moon takes up only about half of a
degree or about 31 ark minutes in the
night sky.
Gaminga traveling 0.2 two arc seconds
across our sky each year may not sound
like a lot, but from our perspective on
Earth, the typical star only moves a few
thousandth of an arcsec per year. Yet,
despite being [music] 800 lighty years
from us, Gaminga will travel 30 ark
minutes, the equivalent to the apparent
diameter of the moon across our sky in
just over 10,000 years. In other words,
this stellar corpse is racing through
the galaxy at nearly 210 km per second
heading towards the border between the
constellations Gemini and Lynx. And at
its current rate of motion, Gaminga will
remain in Gemini for another half
million years. But it may need a new
name after that. However, this
mysterious pulsar gets stranger still.
It is its vast speed that helps produce
another feature that scientists were
about to discover. As it hurles through
space, Gaminga leaves behind two ghostly
X-ray tails that streak 3 trillion km
across the sky.
As I discussed earlier, despite the fact
that this fastmoving pulsar is nearly
radio silent, it certainly isn't [music]
quiet in the gammaray and x-ray
wavelengths.
In 1999, issa's x-ray multi mirror
mission or XMM Newton was launched to
peer deeper into this X-ray universe.
And four years later, a team led by
Patrica Caraveo uncovered these
cometlike X-ray trails. Their shape and
brightness are partly explained by the
shock wave created by Gaminga's motion
through space and its rotation as a
pulsar. But they are also revealing of
another attribute. Gaming's colossal
mass.
Measuring only about 20 to 30 km across.
Gaminga is extremely dense containing
about as much mass as 1 and a half of
our suns. To put that in perspective, if
you had a teaspoon of neutron star
material, it would weigh about 4 billion
tons, as much as 10,000 Empire State
buildings.
As this dense, high mass object races
forward through the low density
interstellar medium, just 0.06 to 0.15
atoms per cubic cm. It compresses the
interstellar medium and its own embedded
magnetic field by a factor of four.
Meanwhile, the incessant spinning of the
neutron star creates an environment
where electrons and their anti-atter
counterparts called posetrons can be
accelerated to extreme energies powerful
enough to emit high energy gamma rays.
While most of these electrons are seen
in the gamma radiation that escapes from
the pulsar, some get trapped and spiral
within this enhanced magnetic field. In
these images from a computer model, the
tails can be seen streaking along the
edges of Gaminga's three-dimensional
shock wave, like the wake created by a
boat going through water. Only this boat
is more massive than our sun, and the
wake is made up of extremely high energy
X-rays.
But the final piece of the Gaming puzzle
wasn't discovered until 2005.
Its nebula.
Taking the form of a shell of neutral
hydrogen gas with a radius of 0.4 parex
wide. It turned out to be what we call a
pulsar wind nebula.
This type of nebula is created from the
wind plasma that emanates from a
pulsar's magnetic poles. The plasma made
of charged particles that can be
accelerated to near light speed
surrounds the pulsar, creating a nebula
of high energy particles that give off
strong X-ray emissions. With the
confirmation that Gaminga did have a
nebula, its identity as a pulsar could
finally be confirmed. But Shandra went
even further.
In addition to imaging Kaminga, Shandra
also looked at a second pulsar called
B0355
+ 54. And by comparing the two,
astronomers uncovered another possible
explanation for the absence of radio
pulses from Gaminga. On the surface,
these pulsars seem quite similar. They
are both about half a million years old,
and they spin about four to five times
per second. However, as you know,
Gaminga is seen primarily in gammaray
pulses with no bright radio emissions.
By contrast, the other pulsar, which
I'll refer to as pulsar B, is not seen
in gamma rays and instead is one of the
brightest known radio pulsars.
How could these two pulsars be so
similar yet so vastly different in how
we see them? The answer may be as simple
as how each of these pulsars are
oriented relative to our observation
from Earth.
Astronomers believe that these images of
Gaminga and Pulsar B have revealed their
spin axes and uncovered a reason for why
radio and gammaray pulses may be present
or absent on different pulsars.
Like our own magnetic field around
Earth, both of these pulsars have
magnetic poles close to their spin
poles. These poles are where the beams
of pulsing radio emissions come from.
You could try to model this if you
skewer a little foam ball right down the
middle. The foam ball is a pulsar, and
the radio beams coming from the poles
are represented by the wooden skewer
coming out both ends. If you spin the
ball around the skewer like a spin axis,
you create an equator around the middle.
To illustrate the gammaray source along
the spin equator called the Taurus, you
could cut a hole in a paper plate and
squeeze it over the foam ball. Now
you've got yourself a disc of gamma rays
beaming out from the equator in every
direction. With gaming, the edge of the
paper plate is pointing towards us,
meaning the gamma rays are heading to
Earth. But for pulsar B, its relative
position to us is at a different angle
as if looking at the flat surface of the
plate. The gamma rays are moving
perpendicular to our line of sight,
therefore missing Earth.
Let's look again at the two Chandra
images of Gaminga on the left and Pulsar
B on the right along with artist
illustrations of what astronomers
believe the Pulsar wind nebulas look
like for each of these. In the image of
Pulsar B, the long trailing blue tails
represent the radio jets emanating from
its poles and the skewers coming out of
both ends. Only instead of being
straight like a wooden skewer, Pulsar B
is moving so fast through space that
these jets appear bent backwards,
trailing behind as the pulsar moves
through space. Now look at the image of
Gaminga here. The long twin tails on
either side of the image are the radio
jets trailing behind as it too rushes
through space. But this time, instead of
pointing almost directly toward and away
from our vantage point on Earth, these
jets appear to be coming off to the
sides, not aimed at Earth. So when
astronomers look at Gaminga, they see
powerful gammaray emissions from the
spin equator, but the radio jets point
to the sides and remain unseen. And when
they look at pulsar B, the opposite
happens. The radio jets are pointed
almost straight toward our planet while
the gammaray source at the equator is
missing Earth. Sometimes the most simple
explanation is the correct one. And that
finally brings us back to the decades
long mystery of an unusual abundance of
antimatter bombarding our planet.
For more than a decade, a particle
detector called the Alpha Magnetic
Spectrometer or AMS2 has been attached
to the International Space Station,
collecting information on antimatter,
dark matter, and cosmic ray sources. As
a reminder, cosmic rays are energetic
particles, [music] fragments of atoms
that travel through space at nearly the
speed of light. These can be made by the
sun, by supernova explosions, or other
cosmic means. And in 2013, the first
results of the AMS2 experiment were
announced. The detector had recorded
more than 400,000 positrons, the largest
sample of cosmic ray posetron data ever
collected and increasing the world's
total cosmic ray posetron data by
100fold.
For years, many astronomers and
physicists hoped that this excess
antimatter may be the byproduct of a
dark matter annihilation, [music]
offering possible clues about this
mysterious substance. After all, dark
matter could make up around 27% of the
cosmos. And yet, we still don't know
what it is. Like regular matter, dark
matter holds mass and takes up space.
But it doesn't seem to absorb, reflect,
or interact with light. at least not in
a way we can detect. Some theorize that
dark matter may be made of yet
unidentified types of particles.
Whatever it is, scientists had high
hopes that the overabundance of
antimatter being detected aboard the ISS
may hold clues about dark matter's true
nature.
Unfortunately, they've been left
disappointed. The more scientists dig
into the data, the clearer it's
becoming. The most likely source of
these posetrons may actually be pulsars.
Astrophysicists had long suspected this,
but until 2017, there simply wasn't
proof. It was the high alitude water
Cherenov Gammaray Observatory that
finally added evidence to this
hypothesis. A small halo of gamma
radiation was identified surrounding
Gaminga with trillions of times more
energy than is visible to our eyes. from
5 to 40 trillion electron volts, the
sort of radiation usually produced by
posetrons. This was the first real
observational evidence pointing to a
pulsar as a potential source.
Pulsars naturally surround themselves
with a haze of both electrons and their
posetron counterparts as a result of the
stars intense magnetic field. This
intense magnetic field pulls particles
from the pulsar surface and accelerates
them to near the speed of light.
Scientists think that these accelerated
posetrons and electrons are then
colliding with starlight boosting the
light to higher energies which then
radiates as the gammaray halo observed.
But based on the size of the halo the
hawk team saw gaming posetrons would
rarely have the energy required to reach
our planet. And so they believed the
excess posetrons must have a more exotic
source. That was until stunning new
information was uncovered a few years
later thanks to a team led by
astrophysicist Matea Dearo
using a decade of gammaray data from
Gaminga acquired from Fermy's large area
telescope which is able to observe lower
energy light than the Hawk gammaray
observatory. The Maro's team was able to
subtract out all other gammaray sources
to reveal a spectacular glow coming from
Gaminga, much much bigger than what the
scientists had ever seen before.
The vast oblong halo of glowing gamma
rays at an energy of 10 billion electron
volts spanned 20° of the sky, similar to
the area the Big Dipper constellation
occupies. And that's not all. The glow
of gamma radiation is even bigger at
lower energies. If we could see it all
with the naked eye, Gaminga's gammaray
glow would dominate our sky, covering an
area 40 times bigger than the full moon.
With this new information,
astrophysicists found that the size of
Gaming's halo meant that this one pulsar
alone could be responsible for as much
as 20% of the excess posetrons detected
near Earth. From there, it's no stretch
to imagine that other pulsars are the
most likely culprit for the remaining
antimatter abundance we found. This
explanation may not have solved the
mystery of dark matter, but it is
certainly a magnificent revelation.
It was Jocelyn Bell who discovered the
first pulsar in 1967, back when people
thought that those regular signals could
be the work of extraterrestrial life. In
the nearly 60 years that have passed
since, we have found thousands of
pulsars, and our understanding of these
neutron stars has grown with everyone.
And since Gaminga was identified as only
the third known gammaray pulsar in 1991,
we've now spotted over 300 thanks to
NASA's Fermy mission. But given
Gaminga's track record of defying
expectations and furthering science, I
like to think that this particular
pulsar has more secrets still to reveal.
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