- 4388 - DARK MATTER - what have we learned? - Most, if not all galaxies are surrounded by halos of this mysterious, unknown, but ubiquitous material, called Dark Matter. It played a role in galaxy formation. The nature of that role is something astronomers are still figuring out. Today, they’re searching the infant Universe, looking for the tiniest, brightest galaxies. They could help tell the tale of dark matter’s role in galactic creation.
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4388 - DARK MATTER
- what have we learned?
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- Astronomers use
computer programs that can track the circumstances of galactic births not long
after the Big Bang. These computer models take into account previously
neglected interactions between dark matter and the primordial “stuff” of the
Universe, hydrogen and helium gas.
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- How would
interactions between “baryonic matter' and dark matter make a difference? In the early Universe, clouds of gas moved
at supersonic speeds past clumps of dark matter. It bounced off the dark
matter. Eventually, after millions of years, the gaseous material fell back
together to form stars in a blast of star birth.
-
- The existence of
those smaller, brighter, more distant galaxies could confirm the so-called
“cold dark matter” model. It suggests that the Universe was in a hot dense
state containing only gases after the Big Bang. Over time, it evolved to a
lumpy distribution of galaxies (and eventually galaxy clusters).
-
- Along the way,
stars and galaxies formed, but the earliest steps likely depend on
gravitational interaction with dark matter. If there were supersonic
interactions then those little galaxies would be the result.
-
- JWST has seen some
pretty early galaxies during its time in operation. It hasn’t detected the very
earliest ones. However, the images it
HAS provided are tantalizing hints at what might exist in earlier epochs and
could provide insight into the role of dark matter.
-
- The discovery of
patches of small, bright galaxies in the early universe would confirm that we
are on the right track with the cold dark matter model because only the
velocity between two kinds of matter can produce this type of galaxy. If dark matter does not behave like standard
cold dark matter and the streaming effect isn’t present, then these bright
dwarf galaxies won’t be found.
-
- JWST needs to
begin to look for galaxies that are much brighter than expected. If they exist,
that will likely prove the interactions occurred early in cosmic time. If none
can be found, then maybe scientists still might not understand dark matter
interactions. If they exist, then how did they form so quickly and why are they
so bright?
-
- The standard
cosmological model says that the gravitational pull of clumps of dark matter in
the early Universe attracted ordinary matter. Eventually, that caused stars to
form, followed by galaxies. Dark matter is thought to move more slowly than
light. So, astronomers predicted that the star- and galaxy-formation processes
happened very gradually.
-
- But, what if
something else was going on more than 13 billion years ago? How would that
change things? It was a time before the first galaxies formed. But, it was a
time when ordinary matter in the form of large over densities of hydrogen and
helium gas streamed through the expanding Universe.
-
- It bounced off
slower-moving clumps of dark matter and outran its gravitational pull, at least
for a time. Then, the baryonic matter massed together again, under the
influence of dark matter. That’s when the star birth fireworks began.
-
- While the
streaming suppressed star formation in the smallest galaxies, it also boosted
star formation in dwarf galaxies, causing them to outshine the non-streaming
patches of the universe. The
accumulated gas began to fall together after millions of years. That led to a
huge burst of star formation.
-
- Lots of massive
hot, young stars began to shine, out-brilliancing the stars in other small
galaxies. Ultimately what this means is that since dark matter is impossible to
“see”, those brightly shining patches of galaxies could be indirect evidence of
its existence. And, prove the role dark matter played in the creation of
galaxies.
-
- The discovery of
patches of small, bright galaxies in the early universe would confirm that we
are on the right track with the cold dark matter model because only the
velocity between two kinds of matter can produce these type of galaxy.
-
- JWST is a perfect
telescope to help see these galaxies. It should be able to peer into regions of
the Universe where tiny infant galaxies are brighter than astronomers expect
them to be. That extreme luminosity will help JWST spot them, showing them as
they looked at a time when the Universe was only a few hundred million years
old.
-
- Because dark matter
is impossible to study directly, searching for those bright patches of baby
galaxies in the early Universe could offer an effective test for theories about
dark matter and its role in shaping the first galaxies.
-
-
March 14, 2023 DARK
MATTER - what have we learned? 4388
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