We do not know the Milky Way galaxy.
Yes, even though we are in it. Before
you think I'm talking about niche
details about stellar formation, how
galaxies evolve or things like that, I'm
not. Even some of the basics about the
Milky Way are mysteries to us. Like, how
many stars are here? What is its basic
shape? Specifically, does its spiral
have two arms or four?
Although those might seem like simple
details, we don't actually know them.
Number of stars estimates range from 100
billion to as high as 400 billion
depending on what estimates are being
used. Scientists have gone back and
forth between two or four arms over the
last two decades, and currently we're
leaning towards four. This makes sense.
It's naturally harder to look at a thing
that you're inside. It's easier to look
out your window at the house across the
street than it is to look at your own
house from that same position. But
here's a fun one for you. How many
galaxies are in the Milky Way galaxy?
According to Gaia Space Telescope, which
just finished its 10-year mission, the
answer is not just one. Gaia has been
mapping the stars of the Milky Way,
performing 3 trillion observations. And
now, as it takes its final look at our
galaxy, the data is being evaluated.
30,000 stars are moving a little
strangely. They are going the wrong way.
They are originally not from around
here. I'm Alex Mccoan and you're
watching Astramm. Join me today on a
deep dive into Gaia's data to answer
exactly how many galaxies did the Milky
Way eat?
As I already alluded to, looking at our
own galaxy is surprisingly hard. I've
mentioned before in a previous video how
all of the stars, stellar clouds, and
gas can actually get in the way of what
we're trying to look at. This gets
particularly bad towards the center of
the Milky Ways plane where the most
matter accumulates, creating an area
astronomers referred to as the zone of
avoidance.
Visible light cannot easily penetrate
this zone, leading scientists to resort
to other mediums like X-rays to
scrutinize what lies beyond. To carry on
our house analogy from earlier, we are
sitting in our bedroom trying to figure
out the layout of the rest of the house.
But the walls right in front of us are
preventing us from seeing any of the
other walls and rooms. Further
compounding this is the difficulty in
telling how far away a star is from
Earth. To make an accurate 3D map of the
Milky Way galaxy, you need to know if
the stars you can see are dim, small,
close ones or large, bright, distant
ones that only look dim and small
because of their distance. Not all stars
make this easy. While some type of stars
such as seed variable stars have a
predictable enough luminosity that their
distance can be calculated if you know a
few things about them, not all are quite
as accommodating. So for unpredictable
stars, how can you tell how far away
they are? The answer is parallax. And
that's what Gaia has been using over the
last 10 years for its galaxy map.
Parallax is the principle that depending
on your point of view, things can appear
to be in different places. You can see
an example of this right now by holding
up your finger in front of your face.
Close one eye, then instead close the
other. Now, alternate quickly between
the two. See, your finger moves quite
significantly in relation to its
background. The closer an object is, the
greater the effect of parallax. Simple
trigonometry takes care of the rest,
allowing you to calculate how far away
an object is. While this effect was very
noticeable based on a finger in front of
your face, you'll see much less parallax
on a tree on the other side of a field,
which means it's further from you. The
further away something is, the harder it
is to use parallax to tell you its
distance. Things can get a little
imprecise.
But how then can we use this method to
calculate the distance to a star? The
secret is to widen your base viewpoint.
Just as the distance between your eyes
can influence the effect of parallax on
an object, Gaia viewed stars not just
once but multiple times over the course
of a decade. In that time, the face of
our night sky will have changed as we
can see in time- lapses like this one
with an exaggeration of 10,000 times.
Rather than using the 6 cm between your
eyes as the base, every half year we can
make the solar system our base instead.
Our Earth moves from one side of the sun
to the other, which causes parallax
effects to be visible in every star we
see. Note how in this animation, the
stars are taking little looping
patterns. That's not really how they're
moving, but how we are. That's the
effect of our own loops around the sun.
This can help with measuring stars
distance, but there's actually an even
larger scale we can use. The proper
motion of stars.
We can ignore the loops for this one as
an even larger base is coming into play.
Rather than just use the motion of our
planet on either side of the solar
system, we can make use of the fact that
our own solar system along with the
other stars in the galaxy are also
moving. So we can use that motion as an
even larger base for establishing
parallax. The same principle applies.
Stars with proper motions against the
backdrop of space are closer while stars
with less proper motion are further
away. In this way, Gaia has been
building a precise 3D map of two billion
stars in our Milky Way galaxy and beyond
over the course of three trillion
observations.
But Gaia has not just been looking at
their motion and distance.
This telescope was to study the
luminosity, temperature, mass, and
chemical composition of these stars,
too. It houses two powerful telescopes
that channel light from two different
directions into a camera with nearly a
billion pixels, the most precise camera
in space.
Its radial velocity spectrometer can
measure Doppler shift to give us clues
about its velocity. It also has
phototric instruments to reveal spectral
information about each stars properties
like composition and temperature. So
although 2 billion stars is only a drop
in the ocean of the 100 billion stars
thought to inhabit the Milky Way, this
still allows us to create an incredibly
detailed map of our galaxy over time.
And it's that over time bit that allows
us to see the Milky Way's eating habits.
Since 2013 when Gaia was launched, it
has been collecting data which issa
scientists have been processing and
releasing in large data packets for the
general scientific community to study.
The larger the gap in time, the more
comprehensive and precise the data. More
time equals more parallax. Three such
data releases have taken place so far in
2016, 2018, and a two-parter that
released a simplified version in 2020,
and then the full version in 2022.
And scientists have already had the
chance to evaluate what Gaia has seen.
And as they witnessed the motions and
locations of stars in our galaxy over
time, it became possible to model the
whole galaxy and even wind it backwards.
Take a look at this.
It's impossible to photograph our own
galaxy as no camera equipped spacecraft
has traveled out that far. But here is a
representation created using Gaia's data
of what it looks like to an
unprecedented degree of accuracy.
Note its wobbly edges. These indicated
to scientists that the Milky Way crashed
into another galaxy in the distant past.
Using the second data release,
researchers from the Netherlands looked
at 7 million stars and found that 30,000
of them were moving strangely. While
most stars, including our own, move
around the Milky Way in one direction,
this odd collection was moving the
opposite way. Their color and brightness
were also strangely distinct, indicating
there was something special about this
particular group. The researchers ran
the numbers and found that a model that
fitted their observations was what would
happen if another galaxy collided with
our own.
The collision must have happened 8 to 11
billion years ago and involved a small
dwarf galaxy that the researchers called
Gaia Enceladus or sometimes the Gaia
Enceladus sausage.
See how its stars indicated here in red
actually managed to retain a fairly
discreet form for a time before
eventually spreading out across the
Milky Way. This merger may have been an
important part of how our Milky Way came
to have some of its unique
characteristics such as a bar in the
center. Something that only 2/3 of
spiral galaxies have the Milky Way
didn't go in for a little late night
sausage eating just once though. Another
dwarf galaxy known as Aruya Seoia Latoy
was also found to have merged with the
Milky Way and perhaps was a binary
pairing with Gaia and Celadus. And then
in a later study, another dwarf galaxy's
remnants were found more than one. In
fact, according to this study, our Milky
Way may have eaten as many as six other
galaxies. Gaia data reveals this hasn't
stopped. The nearby dwarf galaxy
Sagittarius has collided with our own
three times already in the past 4 to 5
billion years and is set to do so again.
This collision may have even been the
spark that lit the flame of our very own
sun which came into being around that
same time.
Eventually, Sagittarius may well become
galaxy number seven that the Milky Way
has consumed. all of its stars being
slowly ripped away and brought into our
own galaxy.
These revelations are just some of the
incredible discoveries made possible
through the Gaia telescope's data, which
is why it is sad that Gaia's time has
come to a close.
The Gaia telescope maintained its
position in the second Lrangee point
using judiciously applied cold gas
propellant a dozen grams a day. However,
that cold gas has finally run out. On
the 15th of January, Gaia took its last
observation and has begun the process of
doing a few last calibrations before
finally powering down on the 27th of
March, 2025.
But its story is not over yet. Two more
data packets await release. The first of
the two, data release 4, will include
500 terabtes of information and will be
released in 2026. It will only cover the
first 5.5 years of Gaia's mission, but
will do so to an incredible level of
detail. Its precise measurements of
stars wobbling motions might even
highlight possible locations of
exoplanets and will create the largest
catalog of binary stars to date.
It's also worth recognizing that the
discovery sky brought us don't end with
just prior or ongoing galaxy impacts.
It's possible to fast forward the data
to model the motion of our local stars
millions of years into the future,
allowing us to see incredible models
like this one. Note how although the
stars near us initially spread out
across the Milky Way, they later
reconvene due to what is thought to be
density waves. Seeing this play out
helps explain the spiral arm shape of
our galaxy.
Gaia data has helped improve our picture
of events much closer to home, too. Gaia
revealed the position and direction of
travel of over 150,000 asteroids in our
solar system. And thanks to its ability
to track those movements over time, Gaia
was able to demonstrate that 352 of them
probably have moons as shown by slight
wobbles in these asteroids trajectories.
This nearly doubles the number of such
binary system asteroids that we are
aware of.
[Music]
Gaia has been called a treasure trove
and it's hard to overstate just how much
information can be found in these data
releases. Gaia has provided us with the
largest ever 3D map of quazars across
the wider universe identifying 1.3
million of them with the earliest being
spotted at the edges of the universe
with light that started traveling when
the universe was only 1.5 billion years
old. Gaia has found a previously unknown
black hole in our Milky Way, 33 times
the mass of the sun and only 2,000
lighty years away from us. This type of
black hole had never been seen in our
galaxy before. Most local black holes
are only 10 times the mass of the sun,
making this new find truly massive.
Many more such discoveries can be found
thanks to Gaia data. It's no surprise
that issa is already considering plans
for a Gaia replacement. Gaia NIR, a
space telescope similar to Gaia, but
able to see much further into the
infrared to peer through the gas clouds
that obscured Gaia's vision. But don't
hold your breath for this one. If it
goes ahead, GIA NIR will look to launch
in 2045
to provide an approximate gap between
that mission and GIA. To allow ISSA to
take even more advantage of parallax
effects, Gaia NIR will be able to see
how much further Gaia's observed stars
have traveled in the intervening time.
When it comes out, data 5 will be the
big one. Tentatively set to be released
by the end of the decade. This data
release will include everything, all
10.5 years of Gaia's mission to the
highest level of detail imaginable. It
will truly be a treasure trove of
information. Just think what discoveries
can be made with so much raw data to
sift through. Who knows what else we
will learn about our galaxy.
So, while Gaia's mission coming to a
close is sad, the wealth of data it has
collected is also very exciting. Our
Milky Way galaxy might be surprisingly
hard to learn about, but Gaia's data
will give us the best crack at it to
date.
We've all seen pictures of galaxies,
often glorious objects with spectacular
colors and shapes.
However, because they are static images,
it may make you wonder how they rotate.
The first obvious thought is that they
spin around an axis, perhaps looking
something like this as they do so.
Would it surprise you to hear that this
is totally wrong?
For a start, galaxies are not solid
objects, but rather made up of millions
to trillions of stars. Each star follows
their own orbit, although they are often
going in the same direction at least.
But actually, one of the main reasons a
spiral galaxy does not orbit like the
first example is that angular momentum
would wind the arms up into tighter and
tighter spirals.
We don't see this, so something else is
at play.
The leading theory is that these arms
are caused by density waves, meaning a
galaxy's rotation would in fact look
like this. Here, the arms stay in place,
or at least move extremely slowly as
stars and gas pass through them.
Another theory is that shock waves
produced by supernova and stellar winds
are the cause of the arms. These
theories might not be mutually exclusive
and both processes may be at work here.
Density waves are potentially caused by
the self-gravity of stars as they orbit
after they have been perturbed by
another force.
As stars have a gravitational influence
on each other, eventually a pattern
forms where their orbits meet around
certain areas in the galaxy.
Very very interestingly, density waves
are even seen in certain parts of
Saturn's rings. Here you have a section
of ring that appears like the inside of
a tree trunk. But this is not the case.
In this region, the ring is influenced
by the gravity of small shepherd moons
tucked inside the rings. What you are
actually looking at is one very tightly
wound ring, a bit like an LP record. And
just like with a galaxy, this arm stays
the same shape, never getting tighter or
looser.
Within these arms is where the majority
of star formation takes place in a
spiral galaxy. The gas and dust within a
galaxy clump up in these arms, too,
which is why you often see star form in
nebula dotting the arms. The arms are
also brighter, not just because there
are more stars here, but also because
all the hot, young, bright stars are
found in these regions.
Because the hottest types of stars are
so short-lived, by the time they move
away from the arms, a lot of them will
have already burned out.
Another interesting phenomenon to do
with spiral galaxies is something caused
by dark matter. In the early universe,
when dark matter was more disperse,
stars within galaxies that are dominated
by normal matter would orbit a lot
slower around the outside of the galaxy
than towards the center.
However, today stars are moving a lot
faster near the edge of the galaxy
thanks to the influence of dark matter.
Dark matter is mysterious in that it
cannot be seen or observed in any way
other than by its gravitational
influence.
Dark matter seems to have clumped
towards the center of galaxies over
time, making stars orbit faster than
they should around the edge of a galaxy
if only gravity from normal matter was
accounted for. Other theories also exist
about why this may take place, but these
would have to change the way we
currently understand physics.
Anyway, how do we know about this change
in the way stars orbit galaxies? Well,
of course, we can see back in time when
we look at extremely distant objects.
Stars within galaxies billions of light
years away seem to orbit slower than
stars much closer to us, and this effect
scales depending on the distance to the
galaxy.
Of course, though, there are some rule
breakers out there. While most galaxies
have stars that orbit like this, a few
have been spotted that have leading
outer arms. One example is NGC 4622,
a bizarre galaxy that rotates in the
direction the arms are pointing. This
was hard to accept at first until
smaller inner arms were also found.
This unusual galaxy has probably
experienced a merger in its not too
distant past which likely caused this
phenomenon.
Another rule breaker is the black eye
galaxy which has two counterrotating
discs of gas and dust. The inner disc
where you can see all the dust lanes
rotates normally whereas gas in this
outer disc rotates the opposite
direction. Interestingly, stars in this
outer region do not seem to be orbiting
retrograde, meaning it is just the gas
that does so. It is believed that gas
must be still getting fed into the
galaxy from the intergalactic medium or
that this galaxy also merged with
another extremely gas-rich galaxy.
[Music]
The last thing I wanted to show you
today is the other major category of
galaxy, elliptical galaxies. Elliptical
galaxies contain stars that are
generally much older than those found in
spiral galaxies because the dust lanes
in these galaxies have been exhausted,
meaning stellar production has all but
stopped.
In these kind of galaxies, stars are
very much independent from each other
following their own rather elliptical
orbits. Sometimes galaxies can exhibit
characteristics of both types of
galaxies. These are known as lenticular
galaxies.
These galaxies have dust rings which
haven't fully been exhausted yet and
they have quite a ghostly appearance.
Star formation does appear to be a
factor in keeping spiral arms defined as
once the stellar building blocks dry up,
we've seen examples of spiral galaxies
losing their definition. Perhaps
lanticular galaxies are the midway point
between spiral galaxies and elliptical
galaxies.
So, there we have it. A look at how
galaxies rotate.
The universe is full of secrets, and
some of the most incredible ones are
hiding just beyond the reach of visible
light. What if I told you that more than
1.5 billion unseen objects from galaxies
and newborn stars to some of the oldest
stars in our entire galaxy are sitting
just out of reach of us cloaked in
cosmic dust.
[Music]
That's a little frustrating to think
about, isn't it? Until now. That is
because thanks to the European Southern
Observatory's Visible and Infrared
Survey Telescope for Astronomy, better
known as VISTA, we can finally lift the
veil on these hidden wonders.
[Music]
For the first time in human history, we
have a pretty comprehensive infrared map
of the Milky Way. one that pierces
through the obscuring fog of space to
reveal an unprecedented view of our
galaxy and what lies beyond.
I'm Alex Mccoan and you're watching
Astramm. Join me today as we appreciate
how this firstofits-kind map was made
and take a look at some stunning images
that reveal previously unknown stars
across our galaxy.
In September 2024, VISTA published the
largest and most detailed infrared
survey of the Milky Way ever undertaken,
encompassing a 13-year period from 2010
to 2023 across 140 nights of
observation. This project has captured
around 200,000 images and generated 500
terabytes of data.
That's the same amount of data as it
would take to stream a 4K video for
nearly 3 years straight. VISTA is part
of ISO's paranal observatory located in
Chile with its main focus being to map
large areas of the sky.
Using Vista's infrared camera known as
Veram, the team was able to peer through
the dust and gas that permeates our
galaxy and uncover some of the Milky
Way's most hidden places.
Traditional telescopes allow us to view
space in visible wavelengths which range
between about 380 to 700 nanome. But
VISTA isn't like traditional telescopes.
Instead of relying on visible light
alone, Vista operates at infrared
wavelengths between 900 and 1,200
nanome, allowing it to detect otherwise
invisible objects like stars obscured by
dust and cold brown dwarfs, also known
as failed stars, which don't emit enough
visible light to be seen with a
traditional telescope.
To get an idea of the difference between
visible and infrared light, take a look
at these two images of the Lobster
Nebula or NGC 6357.
One taken in visible light and the other
with Vista's telescope. We can see that
in the infrared, the dust that obscures
our field of view seems to disappear,
revealing what look like hundreds of
thousands or maybe even millions of
previously invisible stars.
The map was created through Vista
variables in the Via Lakia or VVV
survey. Via Lakia being the Latin name
for the Milky Way and its companion
project, the VVV extended survey or VVX.
The data collected from these two
companion projects that make up the
Vista Infrared Survey have already led
to the publication of more than 300
scientific articles.
Unlike other recent space maps, this is
one of the most detailed ones ever made.
It's the first infrared survey to cover
nearly 80% of the Milky Way's luminous
mass and provides the largest infrared
catalog ever made of our galaxy's
central region. It allows astronomers to
study our galaxy in finer detail than
ever before. This survey gives us an
accurate 3D view of the inner regions of
the Milky Way which were previously
hidden by dust. It covers an area of the
sky equivalent to 8,600
full moons and contains about 10 times
more objects than any previously
published infrared map from 2012.
Our Milky Way consists of a central
bulge, a dense, bright, puffed up
collection of stars with a flat disc of
two spiral arms wrapping from the ends.
This image shows the area of our galaxy
that was mapped in the survey. The red
squares mark the central regions of the
galaxy which were observed by the
original survey and then reobserved
again by the extended survey. And the
other square colors show areas that were
only observed as part of the extended
survey. From this image, you can see
that these surveys have focused right on
the central plane of our galaxy,
spanning part of the disc and most of
the nuclear bulge. But what has Vista
revealed?
Argentinian astrophysicist Dante Maniti,
who led the survey project, said, "We've
made so many discoveries, we have
changed the view of our galaxy forever."
And as much as I'd love to talk about
all of them in this video, it's probably
best I stick to some of the highlights.
As part of the survey in 2015, VISTA
turned its attention to the star
formation region of Messia 20, also
known as the Triford Nebula, which lies
about 9,000 light-years from Earth.
Viewed in visible light in this image,
we can see a beautiful nebula glowing
pink from the emission of ionized
hydrogen and surrounded by a blue haze
of scattered light from young hot stars.
The cloud of gas and dust is obscuring
the star-filled space behind it. Now
look at this second image taken by
Vista's infrared camera.
Peering beyond the clouds reveals a
whole swarm of new stars.
This image not only allows us to see
through the Trifid Nebula, but by chance
it revealed objects on the far side of
our galaxy that had never been seen
before. To their surprise, astronomers
identified two faint reened objects as
seeded variable stars. While they appear
in the image to be just behind the edge
of the Trifford Nebula, in reality they
are very distant about seven times
farther than the nebula that once helped
to block them from our view. Seeed
variables are a type of bright star that
is unstable. They brighten and fade over
a period of a few days or a few months
depending on their brightness.
The first variable star we ever
identified in modern times was Omrichon
seti also known as mirror. It had been
described as a nova until 1638 when
Johanna's Halwoods observed it getting
brighter and dimmer in a cycle that
lasted 11 months. As for this pair of
newly discovered stars, they are the
only seaf variables that we have
identified so far in this location which
lies beyond the central bulge on the far
side of our galaxy. And they can be
really useful too. You can think of them
as a kind of cosmic yard stick that can
be used up to distances of tens of
millions of light years. If you know how
long the stars pulsation period from
bright to dim is, then you can infer its
absolute brightness as well as its age,
you can compare absolute brightness to
the apparent brightness, that is the
amount of light that reaches Earth. So
you have a measure of how distant the
star is. With a few reference points
like these, we can build up a real
picture of the scale of our galaxy and
beyond.
Looking toward the galactic center, a
team of astronomers and data scientists
found even more candidate seed stars,
655
in fact. They then sorted these into one
of two classes, and found that 35 of
these 655 stars were classical seafs,
the younger of the two. This was really
exciting, especially since the galactic
bulge was thought to contain mostly
elderly stars that are at least 8
billion years old.
Recording their pulsation periods, the
team revealed that all 35 of these
seafoods were less than 100 million
years old and some of them may be as
young as 25 million years old. To put
that in context, our own son is about
4.5 billion years old. So the youngest
seafooded has only been around for 0.6%
of our son's lifespan.
The team's exploration of seafs
culminated in another major discovery by
mapping the 35 classical seafs they
found. The team was able to trace a
completely new feature in the Milky Way.
a thin disc of young stars that
stretches right across the galactic
bulge
buried behind thick clouds. It had
remained unknown in all previous surveys
of the region. In revealing this
structure combined with the discovery of
all the seafoods as I mentioned earlier,
scientists have inferred that there has
been continuous star formation along the
midplane of the galaxy for the past 100
million years. There might also be even
younger seafoods that we haven't seen
yet as these stars would be so bright
that they would be saturated in the VV
survey. The fact that we found this thin
disc of young stars within the galactic
bulge is incredible.
We used to think that the galactic bulge
was an ancient feature of our galaxy's
past where exclusively old stars had
formed separately from the stellar disc.
But this finding reveals that things
aren't so black and white and that the
formation of newer stars within the
bulge could be a natural progression of
our galaxy's evolution.
But even more inspiring perhaps is a
discovery by the Vista Infrared Survey
that lies at the ancient heart of our
Milky Way galaxy.
In 2016, for the first time, a type of
ancient star known as Ra Lay, another
variable star was discovered in the
center of the Milky Way galaxy by a team
led by astrophysicist Dante Maniti and
Rodrigo Andreas Ramos. This type of star
is usually found in globular clusters,
which tend to orbit the outer regions of
the galaxy. A globular cluster is a
tightly packed group of stars that
contains tens of thousands to millions
of stars bound together by gravity.
They're also really ancient, containing
a stellar population that can be over 10
billion years old. The team found 12 R
Lray stars during the VVV survey, which
suggests that they might be the remnants
of an ancient globular cluster right at
the heart of our galaxy. This finding
also provides evidence that might help
astronomers to decide between the two
competing theories of how nuclear bulges
form. While some scientists think that
the nuclear bulge forms early in the
galaxy's evolution when multiple smaller
galaxies violently collide, others say
that it forms gradually over time where
gas is funneled inwards to trigger star
formation.
Finding these ancient stars here
suggests that the bulging center of the
Milky Way likely grew through the
merging of primordial globular clusters,
therefore supporting the first theory.
So, not only does it hint at our own
galaxy's beginnings, but it also offers
compelling evidence into how these
galactic bulges might form in other
similar galaxies.
Speaking of ancient stars, Vista was
able to find two new globular clusters
as part of the infrared survey in 2011.
In this visible light image, a known
globular cluster UKS1 can be seen on the
right as a hazy red splotch. This
cluster had been the dimst known
globular cluster until the new
discoveries.
Now compare this same patch of sky, but
this time in vista's infrared light.
Suddenly, we can see what we have been
missing. much more faint than the known
UKS1. We can make out a second globular
cluster, this time in the upper left of
the image, which has been named VVV
CL00001.
Another globular cluster aptly named VVV
CL00002
was found soon after and this small
faint group of stars may be the closest
known globular cluster to the center of
the Milky Way. Did you know that there
were only 158 known globular clusters in
the Milky Way before these new ones were
found by VISTA?
For the survey to identify two more of
these rare stellar objects is quite a
significant accomplishment.
Within this central region of the
galaxy, it's easy for younger stars and
cosmic dust to obscure globular
clusters, especially since their age
prevents them from shining as brightly.
But now that they've been revealed,
these features bring exciting
possibilities for further study. It
could just be an illusion of
perspective. But scientists have
wondered whether VVV CL00001 is
gravitationally bound to UKS1.
If this is the case, then they would be
the Milky Way's first known binary
globular cluster pair. We found binary
clusters in other galaxies like in
Centurus A and the large melanic cloud.
But scientists think it might be when
these gravitationally bound clusters
collide that we get the most massive
globular clusters like Omega Centuri.
So studying a binary cluster right in
our own galaxy could produce some
amazing insights into this process. It's
all speculation at the moment, but it's
definitely cool to think about.
In addition to globular clusters, the
Vista Infrared Survey identified a
multitude of other types of star
clusters. At least 96 new open or
galactic clusters have been found, which
typically contain fewer, younger stars
and are much more common than the
globular type. Like the globular
clusters, they have been hidden by
cosmic dust, but VISTA's 4.1 meter
infrared telescope has lifted the
curtain to show them in all their glory.
Take a look at just a few of these
stunning images we now have of these
objects.
One of these open clusters, VV VVV
CL00003,
is much more difficult to make out in
images compared to the tightly packed
globular clusters. Try and see the
density differences in the stars in this
section of the image compared to the
surrounding regions.
It was found by Vista 15,000 lightyear
beyond the Milky Way center and also
happens to be the first of its kind to
be discovered on the far side of the
galaxy.
The sheer scale of this survey is
staggering. Covering a vast region of
the sky and mapping more than 1.5
billion objects, this data has already
led to fascinating discoveries that are
rewriting our understanding of the Milky
Way and beyond. And that's just the tip
of the iceberg. This survey will serve
as a foundation for future telescopes
and observations, which will hopefully
be able to expand on Vista's legacy with
even higher resolution and sensitivity.
We now have the most detailed 3D map
that has ever been made of the Milky Way
structure and objects, one that unveiled
hidden wonders previously beyond our
reach. And scientists are already
uncovering new galactic features and
reshaping our understanding of the
galaxy. With the information from this
groundbreaking infrared survey, as well
as the recent work from ISSa's GIA
mission in visible light, it's an
exciting time to be an astronomer, and
we can expect a flurry of new insights
about our own galaxy and the universe as
a whole. VISTA's infrared observations
have unveiled dozens of hidden star
clusters and millions of previously
unseen stars. They have revealed new
stellar nurseries where stars are born
and they have broadened our
understanding of the formation of our
Milky Way.
Looking at the sky through different
wavelengths has brought about a new era
of galactic exploration. And I can't
wait to see what else astronomers and
data scientists are going to uncover
thanks to Vista's 3D map.
Have a look at this beautiful image
captured by the James Webb Space
Telescope. Immediately, you'll notice
two types of objects. First, you'll see
the nearby stars within our own Milky
Way galaxy, which look like points of
light surrounded by defraction spikes.
But further in the background, you'll
see entirely new galaxies, each
containing billions of stars smeared out
into elliptical or spiraling blurs. What
you probably won't see are distinct
individual objects within those other
galaxies as they are far too distant and
blend in with all the other sources of
light. But there is one exception to
that rule. One type of object that is so
bright you can make it out from billions
of light years away. So bright that it
stands out from all the surrounding
stars in its galaxy. A quazar.
But what if I told you that a whole
bunch of tiny quazars were hiding in
plain sight right within our own Milky
Way? How can that be when they are some
of the brightest objects in the
universe?
In this video, we'll get to see how
that's possible and how a team of
scientists used images of just one
nearby micro quazar to gain a deeper
perspective into the inner workings of
quazars all over the universe. I'm Alex
Mccoan and you're watching Astramm. Join
me today as we unravel the story of
these astronomical lighouses, one cosmic
photon at a time.
Astronomers have been pointing their
telescopes up at the night sky for
centuries. Yet, it was only in the 1950s
that they set out on a quest to map out
what the universe around us looks like
in radio waves rather than visible
light. Think of this as the astronomers
version of putting on night vision
goggles. At first, they didn't see
anything out of the ordinary. Many of
the same galaxies that emitted visible
light also emitted radio waves. So they
could be seen with or without the
goggles. But then among the stars and
galaxies that were known to populate the
night sky, astronomers saw something
new, something that shone very brightly
in radio waves, but had never before
been seen in visible light. And there
wasn't just one of these objects. By
1960, observations quickly grew until
hundreds of mysterious radio sources had
been recorded across our sky.
At the time, astronomers didn't have a
clue what the origin of these radio
waves could be. For all they knew, the
waves could come from a giant
intergalactic network of alien radios.
But what they did learn from follow-up
observations using more precise
telescopes like the Hail Telescope is
that you could see these objects in the
visible part of the spectrum. They were
just extremely small and faint. They
were far too small to be galaxies. They
appeared as points, not smeared out
blobs in the sky. But they also couldn't
be regular stars because regular stars
don't typically emit much energy at all
in radio waves. For this reason, these
mysterious objects came to be known as
quasi stellar radio sources, which quite
literally translates to something like a
star, but not a star. It emits a lot of
radio waves. That name eventually got
shortened to something that was a little
bit more palatable, quazars.
Even with the catchy name, it took
astronomers and physicists nearly 30
years to really pin down what these
quazars were. And unfortunately, it's
probably not alien radios. Although the
real answer is still extremely
fascinating. It turns out that the
explanation centers around black holes
and not just ordinary black holes, but
super massive black holes that can be
millions or even billions of times the
mass of the sun. Such super massive
black holes are frequently found at the
center of large galaxies. And although
black holes can't emit any light
themselves, they can make quite the
spectacle out of the accretion discs
orbiting around them.
If you want all the details, you can cue
up our older video on quazars here. But
for now, let me just give you a quick
summary. Matter orbiting a black hole
can spiral inward as it loses energy due
to internal friction. Much of that
energy ultimately gets converted into
light that streams outward from the
black hole. But in some cases, the
accretion disc also splits out
relativistic jets of ionized matter
cumated by powerful magnetic fields
along with the spin of the black hole
and its surroundings. The particles in
these jets can propagate through the
universe from galaxy to galaxy as cosmic
rays, sending out radio signals as
they're pushed around by intergalactic
magnetic fields. Overall, quazars emit
so much energy that a single quazar in a
distant galaxy will outshine the other
hundreds of billions of stars in that
galaxy combined.
That's why when quazars were first
observed, they appeared as small as a
star, but far brighter than any star
outside of the Milky Way could have ever
been. Now, the Milky Way has its own
super massive black hole right in its
center, too, called Sagittarius A star.
But for better or for worse, the
accretion disc around our black hole is
too thin and faint to call it anything
close to a quazar. And until something
dramatic happens, like the collision
with the Andromeda galaxy that's
scheduled for a few billion years in the
future, Sagittarius Aar will likely
remain calm and mellow.
On one hand, we're kind of lucky because
a quazar that close to Earth would emit
enough high energy radiation to be
potentially fatal to terrestrial life,
which makes you wonder about the kinds
of life that could arise in galaxies
that do contain quaazars.
But on the other hand, we're missing out
on a second source of light in the sky,
illuminating our planet almost as
brightly as the sun. And it would be so
cool to get to study a quazar from up
close.
So, can you imagine my surprise when I
learned that we might actually have the
best of both worlds? Quazars, alive and
active in the Milky Way, and yet not so
powerful as to wipe out our entire
biosphere.
How could this be possible? If the one
super massive black hole at the center
of our galaxy isn't a quazar, then where
could they be?
It took a couple of decades, but
scientists eventually discovered that
quazars can form around ordinary black
holes, too, not just super massive ones.
These ordinary black holes, just a few
times more massive than the sun,
typically form when giant stars
collapse. So, there are loads of them
spread throughout practically any
galaxy.
You probably wouldn't expect one of
these black holes to have its own
accretion disc, but once in a while, a
nearby orbiting star might get sucked
into its gravitational pull and act as a
source for the smaller, less deadly
version of a quazar, a microquazar.
Even though the jets of a microquazar
are much weaker, they can be easier to
study because of their proximity to
Earth, allowing us to learn more details
about the properties and dynamics of
both microquazars and their larger full
scale counterparts.
The very first micro quazar was
discovered in 1979 and was given the
obvious name SS433
as it was originally documented as the
433rd
entry in a catalog of stars compiled by
astronomers Nicholas Sandelik and Bruce
Stevenson 2 years prior. To date, only a
handful of micro quazars have ever been
found. And SS433 in particular has been
a subject of widespread wonder and
research. Despite its name, SS433 is
more than just some ordinary star in a
catalog. It is a typea super giant
orbiting around a stellar mass black
hole in a binary system. As the black
hole accretes material from the super
giant star, it produces a pair of jets
perpendicular to the line of sight from
Earth, meaning that the jets themselves
will never actually hit us or reach our
detectors. But as the jets propagate
outward, they emit light in all sorts of
directions, allowing us to image them at
various wavelengths and learn more about
how they are produced.
One of the first things we saw was that
there are actually two types of jets
emanating from SS 433. The inner jets
extend out just a couple of light years
from the black hole before fading away,
while the outer jets appear 75 light
years out and span an additional 300
lightyear or so. We still don't know how
exactly these outer jets form or why
they terminate after 300 lighty years.
and we only have a rough idea of what
they're even made of. But a recent study
from the Hes collaboration gave us some
new clues to answer these questions.
One such clue is the presence and
distribution of high energy photons
called gamma rays being emitted by SS
433.
Ordinarily, stars or accretion discs
could not be expected to produce any
gamma rays because their temperatures
are far too low. But the outer jets
coming out of SS433 seem to emit them in
spades.
What's even more surprising is that even
though the outer jets are extremely hot,
the spectrum of light that they're
emitting isn't consistent with an
ordinary thermal distribution of
photons. So what's generating all of
those gamma rays? The current theory is
that the outer jets contain high energy
electrons that can bump into lower
energy photons passing through the
system and they transfer their energies
to the photons during those collisions.
This process goes by the name of inverse
Compton scattering.
The scientists at Hess realized that
measuring the energy in these emitted
gamma rays can give us a lot of
information about the energy of the
electrons in the jets that produced them
in the first place. And what they found
was in full support of the inverse
Compton scattering theory. The highest
energy gamma rays carrying over 10 terra
electron volts of energy per photon or
about 10 trillion times more energy than
a photon of visible light were primarily
coming from the innermost region of the
outer jets. Gamma rays with lower
energies, on the other hand, came from
correspondingly farther distances down
the jets of S433.
This distribution is a clear indication
that electrons farther down the jets
have less energy to transfer to photons
than electrons right at the beginning.
Or in other words, as the electrons
stream along the outer jets, they tend
to lose energy over time, presumably due
to their collisions with photons. But
how did the electrons acquire such large
energies to begin with? Models suggest
that their initial launch velocity from
the black hole was just about 1 quarter
of the speed of light. But by the time
they reach the outer jets, these high
energy electrons appear to be moving at
speeds greater than 99% the speed of
light, multiplying their initial
energies by a factor of 1 billion.
The Hess collaboration believes that
this wild acceleration occurs due to a
shock wave at the base of the outer jets
caused by complicated configurations of
magnetic fields. Each time an electron
interacts with the shock front, it gains
a boost of speed as if it crossed a
boost pad in Mario Kart. And due to the
diffusion of electrons back and forth
within the jet, some electrons can cross
over this boost pad over and over and
over again, like an infinite speed
glitch. This process is called diffusive
shock acceleration, and it may be
responsible for amping up electrons to
energies in the hundreds of terror
electron volts, just enough to be able
to produce the high energy gamma rays
observed by Hess. But shedding light on
the production of photons within the
outer jets of SS 433 is just the
beginning. Micro quazars scattered
throughout the Milky Way can hold
treasure troves of information about the
inner workings of even the most massive
quazars in the center of distant
galaxies. And now that we know to look
for them, micro quazars are less like
hidden gems and more like beacons in the
sky, posing for our astronomers to
capture their beauty in an entire
spectrum of photographs and revealing
ever more shocking surprises.
So, what surprised you from today's
video? Was it the possibility of shock
waves in deep space near black holes? or
was it the fact that the Milky Way is
home to dozens of little quazars of its
own? Let us know your thoughts in the
comments below. Black holes are the
densest objects in existence with
gravity so powerful that even light
can't escape. As such, it comes as no
surprise to find the largest black holes
at the center of galaxies where matter
has been fed into them for billions of
years continually increase their mass.
The very largest of these super massive
black holes can be billions of times the
mass of our sun. However, it may come as
a surprise to you to realize that some
of the most massive black holes we know
of are actually the youngest.
You see, when we look at distant
galaxies, we are also looking back in
time. And the galaxies billions of light
years away often have the largest black
holes. If the universe is only 13.8 8
billion years old and light takes
billions of years to reach us. That
means the galaxy we are observing can
only be a few billion years old at most
from our perspective. Pretty young for a
galaxy.
Surely though, it should be the case
that nearer and thus older super massive
black holes are more massive, seeing as
they've had so much extra time to
consume matter falling into them. So,
what's going on here?
The very largest super massive black
hole we know of is known as ton 618 with
an incredible mass of 66 billion solar
masses. By itself, its mass is
comparable to the Milky Way galaxy.
However, ton 618 is exceptionally far
away and it's taking light emitted by it
10.8 billion years to reach us. Meaning
we are observing it as it was 10.8
billion years ago. This means it can be
at most around 2.8 billion years old. By
comparison, our own Milky Way galaxy is
approximately 13.6 billion years old.
Yet, the super massive black hole found
at our galaxy's core, Sagittarius A
star, is only 4 million solar masses.
The Andromeda galaxy super massive black
hole, while bigger, is still only 200
million solar masses.
One of the big factors to consider here
is the difficulty in detecting and
measuring black holes. This is still a
really new field of research as
technology has only just allowed us to
start observing black holes in the last
few decades. Even then, we can often
only observe the area surrounding black
holes. That is before the event horizon
telescope came along. But even that
telescope takes ages to image just one
black hole. So our general understanding
really is still quite limited. In fact,
most of the distant black holes we know
about can only be seen because they are
quazars.
Ton 618 is a quazar. Matter is pouring
into the black holes accretion disc at
an incredible rate. And because of this,
it's erupted into a quazar. Quazars can
only be sustained as long as matter is
falling into them. Otherwise, they
revert back to dark black holes. It's
hard to fully grasp the physics of the
accretion disc, but it is believed that
the friction here is so great, the
accretion disc of a quazar by itself can
produce thousands of times more light
than entire galaxies combined.
Ton 618 produces as much light as 140
trillion suns, completely outshining the
galaxy it resides in to the point that
we can't even see it from our
perspective.
However, because quazars are the
brightest objects in the universe, they
can be seen from very far away. So, one
reason for large black holes being far
away is down to something known as
malquist bias. This is where brighter
objects further away appear more
plentiful when in reality we simply
can't see the dimmer objects that
distance implying there may be an
argument that the largest super massive
black holes are actually distributed
fairly evenly throughout the universe.
If a galaxy has a very large black hole
but it's not a quazar, it means we won't
see it after a certain distance because
a galaxy is much dimmer than a quazar.
Another reason why we don't see the
biggest black holes close to us is due
to the nature of the universe itself
shortly after the big bang. As you may
know, the universe is ever expanding and
during the early universe, matter was a
lot closer together. Quazars were more
common back then because they need
extreme amounts of matter falling into
them to give off light and there was a
lot more gas around during the early
stages of the universe. Not only has the
universe expanded, but over time, gas
gets converted into stars. Some of the
largest types of stars eventually turn
into neutron stars and black holes
themselves, meaning that they never get
recycled back into gas. Less available
gas means less gas will fall into a
super massive black hole. One of the
theories for the fate of the universe is
actually based on this called the big
freeze where after some trillions of
years all the gas in the universe is
eventually converted into black holes.
Even now we see some galaxies where
their gas has been completely used up
meaning no new stars can form. These are
called elliptical galaxies. Spiral
galaxies still have gas and dust
structures and thus can still produce
new stars. It is interesting that most
of the largest super massive black holes
appear to be in elliptical galaxies
where there is no gas left. Gas needs to
lose momentum to fall into the galaxy's
central super massive black hole. And if
that happened, then the super massive
black hole is likely to be much bigger
because of all the infalling matter.
With elliptical galaxies, this has
already happened. Whereas with spiral
galaxies, this hasn't happened to the
same extent. One such trigger for gas
losing angular momentum could be the
gravitational influence of nearby
galaxies or even collisions with other
galaxies.
In addition, there is less gas available
in the universe now than there was
during the early universe. So, black
hole growth probably occurred rapidly
then, but has slowed down now. This
might be why there is no quazar within
500 million lighty years of us. As the
universe ages and things become less
chaotic and more spread out, the number
of active quaazars has decreased, which
means the only quazars we see, some of
which are the largest black holes we
know of, are the ones that happened a
long time ago.
So why are the largest super massive
black holes often the youngest? Well,
although it may appear that way, it
might not actually be the case at all.
We can measure distant bright quazars
simply because we can see them. Older
and closer black holes may also be
large, but because of Malmquist bias, we
haven't found them yet. As studies
continue and technology improves, we'll
start to get a more complete picture of
the universe around us. With the James
Web Space Telescope nearing its launch,
I felt like it would be a good idea to
have another look at some of the
remarkable images of its predecessor,
the Hubble Space Telescope.
Hubble has been in space for 30 years
now and has increased our understanding
of the universe drastically during this
time. A type of object Hubble has
observed is galaxies.
Galaxies, as we've seen earlier in this
series, come in all different shapes and
sizes with star populations ranging from
millions to the trillions.
They are fascinating, beautiful objects,
each containing its own story of how
they formed the way they did, let alone
the tantalizing question about the
possibility of life somewhere in them.
While we have only observed the tiniest
fraction of the total number of galaxies
in the observable universe up close, did
you know that Hubble has seen galaxies
all the way through their evolution?
From galaxies in the throws of star
birth or starburst to galaxies that are
inert, anemic or dying.
I'm Alex Mccoan and you're watching
Astramm. And today I wanted to look
through this spectrum of galaxy
evolution, focusing today on the
ghostly, beautiful remnants of galaxies
that are on their way out. I hope by the
end of this video to have earned your
like and subscription.
When looking at a galaxy, the first
indicator of the stage of its evolution
is to look at its shape. It is generally
believed that spiral and bar galaxies
are some of the least evolved galaxies
in the universe, whereas elliptical
galaxies are the most evolved.
That doesn't necessarily mean spiral and
bar galaxies are younger, though. It's
just that they take longer to evolve.
Here's an example.
Number 68, NGC 2336.
Galaxies with spirals consist of flat
discs where stars mainly orbit in the
same direction. One of their defining
characteristics are the arms that extend
from the galaxy's center. These arms can
spiral out directly from the galaxy's
core or sometimes the spirals come from
a bar.
They consist of a concentration of
stars, gas, and dust. Galaxies that have
an abundance of dust are likely not as
far along the evolution process as less
dusty galaxies, as this dust has yet to
be turned into new stars. Should no
outside influence accelerate the dust
consumption, a galaxy like this may
produce stars at a fairly slow but
steady rate for billions of years yet.
How do we know it's not producing stars
very quickly? Well, a distinct feature
about this galaxy is the lack of red H2
regions or stellar nurseries. Instead,
while star formation is clearly still
taking place due to all the bright blue
stars you can see in this image, it will
remain as a spiral galaxy for a lot
longer than a galaxy bright with H2
regions.
Like number 69, NGC 972.
Wow, what a pretty galaxy. It almost
looks like it's ablaze with all the
activity happening around it. When a
galaxy is so red, we characterize it as
a starburst galaxy. That is to say, star
formation is happening at an incredible
rate. These red regions are the H2
regions the previous galaxy was missing
an abundance of. As starburst continues,
it will quickly use up the gas and dust
structures you see here, converting it
all to stars. Also notice the blue glow
like a halo around the galaxy. The blue
hue comes from blue stars, the hottest
and most massive star type. This is
another indicator of rapid star
formation, as these stars require huge
amounts of matter to fall into them
during their formation.
Number 70, Messia 61.
Another incredible example of a
starburst galaxy is M61. M61 is a
fantastic galaxy for observation because
it's angled almost exactly face onto us.
This means all the dust lanes and its
red nebula can be studied in detail.
That's a lot harder to do with a galaxy
that's edge on. Looking closely at the
center of the galaxy shows a neat
symmetry with the dust lanes. However,
the further out you zoom, the more you
notice how it becomes less symmetrical.
This arm seems to split into three
whereas this one retains its structure.
Usually an asymmetrical galaxy indicates
that it is being perturbed in some way
either from the gravitational influence
of a nearby galaxy or from an actual
collision with one. In this case, M61 is
actually found 50 million lighty years
away in the heart of the Virgo cluster,
surrounded by over 1,000 galaxies. It's
this outside influence that likely
causes starburst to happen. and for a
galaxy to accelerate its evolution as
this outside tug of gravity causes the
dust clouds within the galaxy to
collapse in on themselves creating
stars.
Number 71, NGC 4921.
All galaxies will eventually exhaust
their supply of gas and dust as they get
converted to stars and then neutron
stars or black holes. A small percentage
of gas and dust also gets consumed by
the super massive black hole believed to
exist at the center of every sizable
galaxy.
What happens to a galaxy then? Well, NGC
4921 is a good example of a galaxy about
to transition into what is known as a
lenticular galaxy. However, this one
still has its spiral arms visible, so it
remains classified as a spiral galaxy
for now. It seems that star formation
and dust lanes are a key element of
keeping the shape of a spiral galaxy's
arms. And when this process stops and
the material runs out, the arms seem to
lose some of their shape and definition.
The color of the galaxy also changes to
a ghostly white or reddish white as the
galaxy's blue star population burns out
and disappears. This is a fascinating
galaxy. It is really unusual to see a
spiral galaxy so devoid of color. The
only colors visible really are the few
remaining blue stars clinging to the
dust lanes. Astronomers have described
this galaxy as anemic as star formation
here must be incredibly slow.
Number 72, NGC 2217.
This is the first true lenticular galaxy
I've shown you today. Although NGC 2217
isn't totally done with star formation
just yet. Notice the blue stars around
the outer edge of the galaxy.
However, in this instance, the dust here
is almost completely exhausted, and the
spiral arms have lost their definition.
The bulge at the center of the galaxy
has a white and reddish hue, showing
that only older and less massive star
types exist here. There are no blue
stars visible to speak of.
Number 73, PGC 10922.
Here's another face on galaxy for you.
This particular lenticular galaxy is
further along its evolution again. Most
of the galaxy here is completely devoid
of gas and dust apart from towards the
center. You'll also notice how any arms
that once existed have been totally
wound up until they are almost
indistinguishable.
All that's left really are old stars and
a flat disc. But even the disc will
eventually lose its shape as the galaxy
widens and evolves into an elliptical
galaxy.
like what is happening with number 74
NGC 1 947.
With this lenticular galaxy, we can
still see the wispy remnants of the
spiral arms. However, the stars in this
galaxy have clearly already stopped
orbiting along a flat disc and now
simply orbit slowly and from all
directions.
The very last stages of a lenticular
galaxy look something like NGC 1533.
There's no gas or dust noticeable.
However, you can just about see the
remains of a bar structure coming away
from the core, indicating that this was
once a bar spiral galaxy.
Eventually, what you end up with is
something like number 76, Messia 105.
This is a true elliptical galaxy, a
galaxy almost totally devoid of gas and
dust. This galaxy is so anemic that only
one sunlike star gets produced in a
galaxy like this every 10,000 years. So
what you are left with is the vast
majority of the stars found in this
galaxy being older, redder star types.
If we really zoom into this image, you
can see the red sprinkling of stars,
especially as we move away from the
brightness of the galaxy's core. This is
the last stage of a galaxy's evolution
that we can observe. These stars will
last for billions to trillions of years.
And the universe is too young to see
what happens eventually to a galaxy like
this. Although it is thought that they
will simply become dimmer and dimmer as
one by one the stars reach the end of
their lives.
So there we have it, a snapshot of the
evolution of galaxies. While having an
almost spooky vibe to them, I really
like lenticular galaxies. Their unstable
nature produces some amazing patterns
that you can't find in any other galaxy
type. Although it is somewhat sad to
think too that as the universe ages,
spiral galaxies will become less and
less common until the only galaxy type
remaining are the elliptical galaxies.
Hubble has released a zip file on their
website containing the top 100 pictures
Hubble has ever taken. What I will do
over the course of this series is go
through these pictures one by one and
explain what it is you're looking at.
And believe me, some of these pictures
require an explanation.
[Music]
Episode 4. For the episode playlist,
click on the annotation here or have a
look in the description.
Number 22, NGC 4449.
At first glance, I thought this was one
of the magnanic clouds, but it's
actually a small irregular galaxy in a
galaxy group called Keen Venati about 12
million lighty years away.
This means like us, it is part of the
Virgo supercluster, otherwise known as
the local supercluster of galaxies. It
is similar to the large magnanic cloud
in that it has a general bar shape. But
the big difference is this is considered
a starburst galaxy. It is very active in
producing new stars as can be seen here
in these pinkish regions. Pink or red
areas in a galaxy are generally a
telltale sign of star formation as stars
surrounded by hydrogen gas ionize the
hydrogen to glow red with intense
radiation.
Another telltale sign of high rates of
star formation is the many blue stars
you see in this picture.
Blue stars are extremely hot, young, and
often massive stars that will burn out
quickly because they get through their
fuel so fast. Because these stars can
only live to a certain age, they must
have only been produced within the last
few million years. And as we can see,
there are many blue star clusters in
this galaxy.
This starburst is thought to be because
of galaxies interacting with NGC 4449.
If we zoom out a bit, we can see this
trail of red stars. Perhaps the remains
of a spheroid galaxy passing through NGC
4449. And it's stretched by this tidal
effect.
Looking at the galaxy center, we see a
bright white group of stars with some
dark clouds of dust around it. Stars can
form within clouds like these.
This galaxy is 19,000 lighty years
across.
Number 23, HD 97950.
This spectacular superstar cluster is
found within NGC 363,
an H2 nebula.
It is incredibly pretty and has been
studied a lot because it's found in the
Karina spiral arm of the Milky Way
roughly 20,000 lighty years away.
NGC 3630
is interesting to astronomers because it
is the most massive visible cloud of
glowing gas and plasma known as an H2
region in the Milky Way. And the
superstar cluster has the densest
concentration of stars known in our
galaxy. The UV radiation and stellar
winds have carved into this surrounding
dust, producing these beautiful shapes,
but also given us an unobscured view of
the superstar cluster. Stars of note in
this cluster are share 25, a star 60
times the mass of our sun and reaching
the end of its life cycle. It's expected
to go supernova any time now as it's
already thrown off matter in a similar
manner to what has been seen in other
supernova.
We also have the three main stars in the
heart of the cluster, barely
distinguishable in the center of these
images here. All three are Wolf Ray
stars, each about 100 times the mass of
the sun and millions of times more
luminous.
Two of them are incredibly close
together as part of a binary star
system, taking only 3.5 days to orbit
one another.
This means they are practically
touching, no doubt exchanging a lot of
mass as well as having an incredible
tidal influence on each other. Zooming
out a bit, we see that visually NGC 3630
is right next to another nebula, NGC
3576.
But in actual fact, this other nebula is
much closer, only about half the
distance to us. They just so happen to
be visually aligned.
[Music]
Number 24, Messia 74. On first glance at
this image, I thought it was another
viewpoint on the famous galaxy we've
already looked at, the Whirlpool Galaxy.
And putting them side by side, these
galaxies do look remarkably similar.
They are both grand design spiral
galaxies for a start and have similar
dust patterns weaving through their
arms.
But putting them side by side, you can
tell that there are slight variations in
these two galaxies. M74's arms are lined
with hot blue stars with pink and red
star forming regions dotted all over.
You may think the arms of the galaxies
like this are static arms rotating
around the nucleus of the galaxy, but
actually they are the visual effect of
density waves. As gas and dust orbits
the galaxy, they pass through the
galaxy's density waves, which compresses
the gas and dust and causes stars to
form. Existing orbiting stars also clump
up in these density waves.
A lot of these stars will be blue and
only short-lived, perhaps completing
their life cycle in only a few million
years.
M74 is about 32 million lighty years
away and has a low surface brightness,
making it one of the most difficult
messier objects for amateur astronomers
to observe and given it the nickname the
phantom galaxy. It is probably just a
little smaller than our own Milky Way
galaxy, containing about 100 billion
stars and being 95,000 lightyears
across.
It sits in the M74 group, a small little
remote group of galaxies.
Number 25, ARP 148. So, first
impressions, what do you think this
could be? Pause the video and take a
guess in the comments if you want.
Well, this bizarre shape found a
staggering 500 million lighty years away
is a galaxy and is nicknamed males
object. It is in fact most likely to be
two merging galaxies. The initial
collision theorized to have created a
shock wave which drew matter into the
center before it propagated out into
this ring. You see the tail is a
streamer of stars from one of the
galaxies, further suggesting this is an
ongoing collision. Interestingly, and on
a little side note, the ARP catalog is
the Atlas of peculiar galaxies.
Number 26, Able 2218.
Now, if you thought the last image was
an impressive distance away, have a look
at this one. Able 2218 is an impressive
cluster of galaxies 2.1 billion lighty
years away. Clusters like these are
particularly scientifically interesting
because these galaxies immense gravity
bends the light around them acting as a
magnifying glass to see galaxies even
further behind them. These long arcs you
see in the image are actually distant
galaxies light stretched and warped by
the gravity of the nearer galaxy
cluster.
In this image is perhaps the most
distant galaxy known at an estimated 13
billion lighty years away. In this image
it's barely visible but in an enhanced
version we can make out its stretched
appearance. Because of this lensing
effect, the galaxy appears twice in this
image. Here as well as here,
we see it from Earth as it was only 750
million years after the Big Bang,
meaning we're looking back in time to
really the early universe.
There are around 10,000 galaxies in this
image.
Number 27, Able 1703.
This is another galaxy cluster doing the
same lensing effect we looked at in the
previous image. I want to explain in a
little more detail about how this
lensing effect works. Firstly, we look
at a distant massive object. Gravity is
theorized to warp spaceime. Perhaps a
topic I'll come to in another video. But
often elliptical galaxies are the
biggest galaxies in existence. And the
more massive the galaxy, the bigger the
warping effect on spaceime. You can see
this with the lensing effect around the
big elliptical galaxy in the middle of
this image. As spacetime is warped,
light is bent around the galaxy. And if
it's aligned right, it gives us a
magnified view of the other side of the
galaxy.
It's a natural handy magnifying glass
just floating in space. And about this
galaxy cluster, Able 1703 is around 3
billion light years away.
Space can be beautiful.
You have flawless elliptical galaxies
with no traces of dust bands blocking
the view of their stunning shape.
You have grand galaxies with spiral arms
that wrap around the entire galaxy with
a surprising level of symmetricity.
And then
you have the ark catalog or the atlas of
peculiar galaxies.
These are galaxies which laugh in the
face of order. galaxies which are often
going through a very tumultuous time in
their existence and they are fantastic
in their own right each with a story to
tell. I'm Alex Mccoan and you're
watching Astramm and in this Hubble
episode we will go through some of the
most peculiar galaxies that Hubble has
ever seen and I'll try and explain what
it is you are looking at.
Number 43, ARP 116 or Messier 60. At
first glance, this galaxy doesn't look
so unusual. It seems like a standard
elliptical galaxy, a massive galaxy
which has already used up most of its
dust and gas in creating stars, which
gives it this smooth appearance. It can
be found 57 million lighty years away
and has one of the biggest black holes
ever discovered near its center at
roughly 4.5 billion solar masses.
But this isn't particularly peculiar so
far.
Zooming out a bit reveals something very
unusual.
M60 is right next to another very
different looking spiral galaxy called
NGC 4647.
From our viewpoint, it looks like the
galaxies should be interacting with each
other, but there aren't any immediate
signs of this. This is very unusual to
see two galaxies so close but without
any warping of their shape. As it turns
out, they are not side by side, but
rather one is in front of the other.
There's one other really unique thing in
this image. Another galaxy you probably
haven't noticed. This tiny little galaxy
here is known as M60 UCD1.
It is the most densely packed galaxy
that we know of. Being only 300
lightyears across, but having 200
million solar masses contained within
it. Towards the center of this tiny
galaxy, stars are so densely packed, it
makes the density of stars about 15,000
times greater than found in Earth's
neighborhood in the Milky Way, meaning
that the stars are about 25 times closer
together. An X-ray view of the
surrounding area from the Chandra
telescope reveals all the black holes
and neutron stars found in Messier 60.
And as you can see, this tiny galaxy
also has an X-ray source, indicating
there is also a black hole to be found
at the center. Scientists believe that
this is a black hole with roughly 10
million solar masses, which would make
it just a bit bigger than the black hole
found at the center of our Milky Way
galaxy.
If this is the case, it is thought that
this galaxy used to be much bigger, but
most of its mass was stripped away,
leaving just this dense cluster of stars
found near the center.
Number 44, ARP 147 or IC298.
You don't have to look too closely at
this image to determine that this is a
very weird looking galaxy. It is in fact
a pair of galaxies that have collided
found roughly 440 million lighty years
away.
This is what the previous galaxies could
end up looking like if they ever collide
because the left galaxy is an elliptical
galaxy and the one on the right is a
spiral galaxy. The collision estimated
to have happened 40 million years ago
caused the spiral galaxy to undergo
extreme star formation seen in the
bright blue regions. The most active
time of star formation or starburst was
15 million years ago and would have
produced the most massive types of
stars. But due to these stars being
short-lived, lasting only tens of
millions of years, most of the biggest
ones have already died as exploding in
supernova
and become either neutron stars or black
holes.
This reddish part of the ring appears to
be the original nucleus of the galaxy.
now just a segment of the ring. Due to
elliptical galaxies having exhausted
most of their supply of dust and gas,
star formation isn't nearly as prevalent
in this galaxy. What you can see though
is the effect of tidal forces causing a
ripple or a shock wave through the
galaxy, which you can see as the stars
have clumped into rings.
[Music]
Number 45, ARP 77 or NGC1097.
Another galaxy with a smaller galaxy
tucked away inside it is NGC 1097.
Unfortunately, the Hubble image cuts the
smaller galaxy out, but ESO's very large
telescope has also had a look at the
galaxies in which you can see its
smaller neighbor NGC 1097A,
a small elliptical galaxy that is in
orbit around the bigger galaxy.
NGC 1097 itself looks quite like a giant
eyeball to me with its pupil surrounded
by a bright iris.
Zooming in on the iris, we can see that
it is a ring rich in star forming
regions. Each of the bright blobs are
thought to be hot bubbles of hydrogen in
which stars are forming.
Viewing different wavelengths of light
shows that some dust from the rings is
also being sucked in towards the super
massive black hole found in the galaxy
center.
But this isn't the most peculiar thing
about NGC 1097.
Zooming all the way out reveals four
jets emanating from the core of the
galaxy in an X shape. Due to the lack of
hydrogen gas found in these jets,
scientists believe that they are the
remains of a small galaxy that NGC 1097
cannibalized.
Number 46, ARP 142.
Here is another galaxy merger that kind
of looks like a penguin and an egg. When
viewed like this, this image might seem
serene almost, but in fact, the biggest
spiral galaxy has taken a beaten from
this merger. This long section here is
where one of the spiral arms of the
galaxy has been ripped away by the
elliptical galaxy, which doesn't look
like it's too phased by this collision,
other than the fact that it looks quite
oblong in shape.
Again, the blue regions along the edges
here contain starburst. And this 3D view
shows that these dust lanes are probably
becoming detached from the galaxy, too.
These galaxies are found roughly 350
million lighty years away.
Number 47, R 2110 or NGC1569.
Now, I don't think you've seen a galaxy
quite like this one. Well, that's
because this tiny galaxy, no bigger than
the large melanic cloud orbiting our
Milky Way galaxy,
is pretty much just one giant nebula.
This galaxy is almost the total opposite
of an elliptical galaxy, as it is rich
in gas and dust that has not yet formed
stars.
NGC569
is found near the Maf group of galaxies
and due to its close proximity to these
much bigger companions. The gas and dust
within it has recently been compressed
causing rapid starburst at a rate 100
times faster than anything observed in
our own Milky Way. Towards the center
are densely packed massive stars which
have blasted away the red dust and gas
towards the outskirts of the galaxy
through solar wind and supernova
explosions leaving behind huge star
clusters.
The small white stars found in the halo
of the galaxy are older stars which have
been around for much longer.
We can have such a detailed look at this
galaxy because although it is small, no
bigger than 6,000 lightyear across, it
is also reasonably close to us at only
11 million lighty years away.
[Music]
Number 48, R272.
We'll finish with one more galaxy merger
seen from a rather interesting angle.
These two galaxies are roughly the same
size and are just astronomical moments
away from impacting each other. There's
also a third galaxy found just above
them, which is also in on the action.
The reason for seeing three galaxies
merging at the same time could be due to
the fact this is happening in the
Hercules supercluster roughly 500
million lighty years away which is one
of the biggest filamentary structures of
galaxies that we know about in the
universe.
You see, the observable universe, as far
as we can tell, kind of looks like a
giant web where galaxies band together
to form these filaments, which form the
boundaries between large voids in the
universe.
This is what the universe up to 500
million lightyear from us looks like.
And even in this space, you can see this
banding of galaxies.
And just because some of you have asked
about this in the past, this is where
Borti's void is, which is one of the
biggest voids of galaxies that we know
about.
Thanks for watching. Making this video
required some long-term planning and
work, which we were only able to do
thanks to the consistency and
sustainability of your memberships as
astronauts on Patreon. A huge thank you
to everyone who has signed up. And if
you'd like us to make more videos like
this, you can join with the link down
below. When you join, you'll be able to
watch the whole video ad free, see your
name in the credits, and submit
questions to our team. Meanwhile, click
the link to this playlist for more
Astrom content. I'll see you next time.