Despite existing on a small planet in a
tiny corner of the cosmos, astronomers
know exactly how much visible matter the
entire universe should contain. The
problem is that for decades, 40% of it
has been missing. And I'm not just
talking about the ever mysterious dark
matter and dark energy. Galaxy clusters
don't seem to have as much visible mass
as our models say should be there.
Entire galaxies seem to have lost huge
reservoirs of the material they were
born with. Even the space between
galaxies, enormous cosmic deserts are
emptier than our best theories predict.
This missing mass has to be out there.
that or all our models of cosmology are
wrong. But every time we've looked,
we've found nothing. And believe me,
we've tried. We've used our most
powerful telescopes, deepest surveys,
and most sensitive detectors in the
search. The missing mass just remains
invisible, slipping past our instruments
like a ghost. That is until now. For the
first time in history, we may have
finally found where the missing mass of
all the universe has been hiding. And
it's in plain sight. Astronomers have
captured images of vast gaseous
filaments that stretch 23 million
lightyear between galaxy clusters. It
may just be one filament, but finding it
has huge ramifications.
Is this the very first detailed image of
the cosmic web? As scientists now hunt
for more, this discovery has the power
to determine whether our cosmological
models are correct.
our cosmic evolution. When we measure all of the gas, dust,
planets, stars, and galaxies, everything
we can see in the whole universe using
everything from infrared to visible
light and beyond to gamma rays, it adds
up to a colossal amount, more than 100
sexilion
kg. That's 10 with 53 zeros after it.
But really, this only accounts for a
small fraction of the total matter that
scientists predict to exist. In fact,
this visible ordinary matter is thought
to make up just 5% of the universe. The
rest is stuff we don't completely
understand. Dark matter is believed to
account for 27%. And dark energy 68%.
Despite their names, dark energy isn't
related to dark matter. What they have
in common is that we can't detect or see
them. Dark energy is thought to be a
seemingly invisible type of energy
causing the universe's expansion to
accelerate over time. And dark matter is
a type of matter that has mass but is
invisible to us as it doesn't absorb,
reflect, or emit any light. I've talked
about dark energy in previous videos,
and that is truly its own mystery. You
can explore those if you're interested
to find out more about the topic, but
for this video, I'll just focus on the
matter at hand. So, 95% of our universe
is likely not made of visible ordinary
matter. And of the 5% that is
technically visible matter, also known
as barionic matter, about 40% has been
missing since the Big Bang 13.8 billion
years ago. Now, I know what you're
thinking. How do we know it's missing if
we've never seen it? We certainly
weren't around back then. Thankfully,
the early universe itself left us the
answer. Measurements of the cosmic
microwave background have allowed
cosmologists to calculate exactly how
much barionic and non-barionic matter
was created as a result of the Big Bang
to an accuracy level of better than a
few%. That gives us a precise budget for
how many atoms should be in the universe
today. But just because it's made of
stuff that's visible to us doesn't mean
it's easy to see. When astronomers go
out and count up all the stars, gas,
dust, and plasma we can see with the
help of models and simulations, we only
find about 60% of what should be there.
The rest has to exist for early universe
physics to make sense. But unless we can
find it, we can't prove that our models
are right. Maybe we've got it all wrong.
Thankfully, scientists haven't been that
quick to give up and instead turned
their attention to working out where the
missing mass may be lurking. And they
came up with an intriguing hypothesis.
Missing barionic matter is not the only
missing mass. And perhaps they're hiding
together. Finding out that 40% of all
has to offer. And now, back to our fascinating discovery.
Nearly a century ago, Swissborn
astronomer Fritz Zviki noticed that
galaxies in the Coma cluster move too
quickly for the amount of gravity that
would be created by their visible matter
alone. Yes, including the missing stuff.
Instead, he thought another form of mass
must be there. And in 1933,
Tiki dubbed this missing substance dunl
materi, the German for dark matter.
In the 1970s, American astronomer Vera
Rubin had a similar experience. She was
observing spiral galaxies and wondered
how stars on the outer edge of the
spiral galaxies were able to move so
quickly without flying off into space
again. Some unknown mass must have been
pulling them back in. And she concluded
the same as Tiki. There must be dark
matter holding them together. This new
type of stuff interacts with its
ordinary barionic counterpart through
gravity, but it doesn't interact with
the electromagnetic spectrum, meaning
that it doesn't absorb, reflect, or emit
any light. This makes dark matter
extremely difficult to find and
seemingly impossible to observe, at
least directly. Yet, it influences the
cosmos on a galactic scale. It may even
be helping to conceal our missing
barionic matter.
Since the 1980s, early observations of
galaxy distribution have revealed a
cosmic pattern, a web like a backbone
across the universe. This skeletonlike
structure has become known as the cosmic
web.
It's thought to have formed as a result
of slight density fluctuations in the
early universe, which can be seen in the
cosmic microwave background or CMBB, a
fingerprint of our universe's ancient
microwave radiation from about 380,000
years after the Big Bang. These tiny
fluctuations in density laid out a
blueprint for where matter would collect
over space and time. where there were
higher densities, more mass would be
drawn in until this great structure was
formed. We already know that CNB
simulations using supercomputers
estimate that dark matter accounts for
five times more of the universe than
ordinary matter. So, it's perhaps no
surprise that the cosmic web is thought
to contain primarily dark matter.
permeating every corner of our universe.
It's made of filaments stretching tens
to hundreds of millions of light years
across the universe. Where filaments
intersect, the concentration of mass is
so great that highdensity nodes are able
to form, containing hundreds or even
thousands of galaxies. The cosmic web is
real. We've mapped large swaths of it.
Our galaxy is part of what's known as
the local group, a collection of a few
dozen neighboring galaxies near to our
own. Our local group belongs to a larger
collection called the Lania
supercluster, which contains some
100,000 galaxies and measures 500
million lightyears across. As you might
have guessed, all these galaxies are
strung along the cosmic web like beads
on strings perched along the edge of
great voids.
But even though we've been mapping this
cosmic web for decades, most of what we
can see is the beads, the distribution
of galaxy clusters along the web, not
the strings that hold them together or
the filaments themselves.
Or is it?
Whilst most of the visible matter in the
universe is tied up in galaxies, not all
of it is, the dark matter in the cosmic
web has a pretty strong pole itself.
There, bound up as vast diffused gas in
those long strings or filaments is where
large scale cosmological simulations
have predicted we might not only find
dark matter but our missing visible
matter too. This low density diffused
gas is known as the warm hot
intergalactic medium.
But simulations are one thing. Detecting
these diffused filaments is another. And
this is where historically we've not had
much luck. Although that started to
change about 20 years ago. In 2005,
NASA's Shandra X-ray Observatory imaged
two huge intergalactic clouds of
diffused gas. We'd seen clouds like this
around our own galaxy and in others
local to us, but not between distant
galaxies.
Could it be gas on the cosmic web? This
was some of the first evidence that the
cosmic web was hiding our missing mass,
but the light was too faint to
completely isolate it, so scientists
couldn't quite be sure. Then in 2012, a
combination of 18 Hubble images was used
to infer the presence of a filament
funneling matter into the galaxy cluster
MAX J0717.
Scientists found it by studying the
distortion of light from background
galaxies due to the gravity of the
filament's dark matter. But again, it
wasn't a direct detection. We still
couldn't say we've actually seen them,
inching ever closer to a discovery. It
was just 2 years later that astronomers
moved beyond indirect detection and
statistical evidence into the realm of
the visible. A team led by Sebastiano
Canalupo from the University of
California observed an enormous filament
of hydrogen gas at nearly 2 million
lighty years across. They spotted it
after it was illuminated by a giant
cosmic flashlight, a bright quazar
shining at it from 10 billion lighty
years away. This was the first time part
of the cosmic web had been seen
directly.
Using the same illumination principle,
in 2019, astronomers revealed whole
networks of hydrogen filaments
surrounding a massive protocluster
directly imaging the web on mega parex
scales. But these detections were only
possible thanks to our cosmic
flashlights. To understand cosmic
filaments as they typically exist in
darkness, we needed a new imaging
technique. And in 2023, scientists made
a breakthrough.
At the WMEK Observatory in Hawaii, a
team of astronomers had designed a
dedicated instrument to search for
filaments of hydrogen, more specifically
dim lyman alpha emission, the spectral
fingerprint of hydrogen as it absorbs
and remits radiation. And it worked. In
fact, they've made entire 3D maps of
these filaments. This was just the start
of the discoveries. In January 2025, the
picture sharpened dramatically.
A team of international astronomers
captured one of the clearest direct
images yet. Using the multi-unit
spectroscopic explorer or Muse mounted
on the very large telescope at the
European Southern Observatory, they
imaged a pair of quazar host galaxies
with a cosmic filament about 3 million
lighty years long. And using supercomput
models built on the Muse data,
researchers were able to simulate a
filament that matches the one they
observed in real life. This was a
spectacular achievement. But there was a
catch. These observations were from the
early universe. They traced cooler
hydrogen gas billions of years in the
past, not hot diffused material thought
to contain most of the universe's
missing varionic matter. Today, our
models predict it stretched along thin
filaments of the cosmic web in the local
universe. But here, the signal is far
fainter and harder to isolate. We were
stuck.
In June 2025,
astronomers finally found what they were
looking for. They were able to isolate
and spectroscopically measure the hot
lowdensity gas of an individual cosmic
web filament in the local universe,
marking a breakthrough moment in our
quest to locate the missing barionic
matter.
A team of European researchers headed by
lead author Constantinos Migas at Leiden
University in the Netherlands used Jax's
Suzaku X-ray Space Telescope to map a
single filament in faint X-ray emissions
over a wide area of space. They then
used the XMM Newton to pinpoint sources
of X-ray contamination, in this case,
super massive black holes, which had to
be removed from the data in order to map
the filament. In this image, you can see
what they found. A filament of the
cosmic web connecting four galaxy
clusters, two on each end, each one as a
white spot surrounded by color. The band
of purple stretched between them
resembling a honeycomb or bone marrowike
texture is the filament of X-ray
emitting hot gas
located in the Sharply supercluster. A
supercluster of more than 8,000
galaxies. The filament stretches across
a distance of 23 million lightyear which
is the equivalent of about 230 Milky
Ways end to end. Its mass comes in at
roughly 10 times that of the entire
Milky Way galaxy. And the temperature of
the filament's hot gas is a scorching 10
million° C. It reveals in detail for the
first time how galaxy clusters are
connected over colossal distances and
uncovers the vast cosmic web that
underpins the structure of our entire
universe. like the very bones of a
cosmic skeleton upon which everything
else forms. And according to the paper's
co-author, the filament is exactly what
we expected from the best large scale
cosmological simulations of the
universe. We got it right.
The latest breakthroughs in observing
filaments lend important evidence and
support for our current standard model
of cosmic evolution known as the lambda
cold dark matter model. The model is
underpinned by dark matter which has
been too complicated for us to catch a
glimpse of thus far. So observing this
once thought missing visible matter on
the cosmic web is a big step in the
right direction. But to truly know
whether our models match reality, we
need more than one or two filaments. We
need to map the entire skeleton or at
least much more of it. And that is where
another mission Uklid comes in. Launched
in 2023, he is Uklid mission is designed
to piece together a more accurate
picture of the cosmic web structure and
history and dig into the nature of dark
matter and dark energy. Uklid will help
us measure galactic shapes with
precision, revealing how dark matter
distorts space through gravitational
lensing and measure red shifts, giving
us a 3D position for each galaxy. This
combination will allow Uklid to infer
the locations of the dark matter
filaments, not just the galaxies on
them, and give us precise locations to
look for more gas. By 2030, Uklid will
likely be able to confirm if the cosmic
web matches results from the XMM Newton
filament discovery and the pattern seen
in the cosmic microwave background. If
it's a perfect match, that would be one
of the strongest confirmations of the
big bang model in the history of
science.
If not, then something is fundamentally
missing in our standard model. Whether
it's our understanding of dark matter,
gravity, or the early universe. Either
way, with the help of Uklid and the
latest observations of these cosmic
filaments, cosmology is poised to be
changed forever.