- 4533 - UNIVERSE - How big is it, really? The James Webb telescope confirms the earliest galaxy in the universe is bursting with way more stars than we thought possible. The light from the most distant galaxy in the known universe suggests that there's something off about our current cosmological models, a new James Webb Space Telescope study finds and the explanations remain elusive.
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- UNIVERSE - How
big is it, really?
-
- The James Webb Space Telescope (JWST) has
spotted the earliest galaxy ever seen, and its unusually bright light is coming
from a bizarre frenzy of star formation.
Named “JADES-GS-z14-0”, the galaxy formed at least 290 million years
after the Big Bang, and contains stars that have been bursting into life since
an estimated 200 million years after our universe began.
-
- Spotted by JWST's Near InfraRed Spectrograph
(NIRSpec) instrument, the mysterious origins and rapid development of the stars
has opened up some fundamental questions about how our universe came to be.
-
- The discovery by JWST of an abundance of
luminous galaxies in the very early Universe suggests that galaxies developed
rapidly, in apparent tension with many standard models. Galaxy formation models
will need to address the existence of such large and luminous galaxies so early
in cosmic history.
-
- Astronomers aren't certain when the very
first globules of stars began to clump into the galaxies we see today, but
cosmologists previously estimated that the process began slowly within the
first few hundred million years after the Big Bang.
-
- Current theories suggest that halos of dark
matter (a mysterious and invisible substance believed to make up 85% of the
total matter in the universe) combined with gas to form the first seedlings of
galaxies. One billion to 2 billion years into the universe's life, these early
protogalaxies reached adolescence, forming into dwarf galaxies that began
devouring one another to grow into ones like our own.
-
- But discoveries made by the JWST confounded
this view. In February 2023, a group of astronomers analyzing data from the
telescope discovered a group of six gargantuan galaxies, aged between 500 to
700 million years after the Big Bang.
-
- The light from “JADES-GS-z14-0” is similarly
puzzling. The light detected by NIRSpec
finds its origins in an enormous halo of young stars surrounding the galaxy's
core, which have been burning for at least 90 million years before the point of
its observation. The galaxy is also crammed with unusually high quantities of
dust and oxygen, which suggests its history of star birth and death may be even
longer.
-
- This finding shows that ultra-bright
galaxies in the early universe are not just the product of active black holes
greedily gobbling up matter, as is often assumed to be the case. The new
observations show that runaway star formation is also a viable explanation for
the surprising brightness of these ancient galaxies.
-
- So how did galaxies like “JADES-GS-z14-0”
produce so many stars, so quickly? Answers to this cosmic mystery remain
elusive, but it's unlikely they will break our current understanding of
cosmology.
-
- If we can see at most 3% of the universe,
how can we estimate the total number of galaxies in it? The Milky Way is just a speck in a universe
filled with an untold number of galaxies. But if we had to take an educated
guess, how many galaxies are in the universe?
-
- The first problem is that even with our
most powerful telescopes, we can see only a tiny fraction of the universe. The observable universe is only that part of
the universe from which the light has had time to reach us.
-
- The universe is 13.8 billion years old, but
the observable universe stretches more than 13.8 light-years in every
direction. That's because the universe is expanding and light got a head start
early on, when the universe was smaller.
Now, the total size in each direction is about 46 billion light-years.
-
- We see at most 3% of the universe. The second problem is that there are so many
galaxies that we can only make estimates of the total number based on what we
can observe in small regions of the universe.
-
- But even that requires a cutoff. "What
do we define is a galaxy?" We
have really giant galaxies that have to have a factor of 10 more" the mass
of our galaxy, "and we have a lot of small galaxies, from lower-mass
galaxies that have about 10 times less mass down all the way to dwarf galaxies.
-
- At some point, scientists need to define a
minimum mass for a galaxy to make estimates possible. If we set a mass cutoff and try to make this
conservative, like a million solar masses, we end up with an average number of
galaxies in the universe from the beginning to today of about 1 to 2
trillion. Scientists think there were
more galaxies earlier in the universe's history than there are today, which is
why galaxy estimates are an average over time.
-
- Those results come from the Hubble telescope
which are near Earth, inside of our solar system, and are limited on what they
can see by all the stuff in our solar system that adds light to the sky. We do have one spacecraft with a camera
that has gotten beyond all the garbage within our solar system, and that's the
“New Horizons spacecraft”.
-
- A 2021 study used the camera aboard New
Horizons to measure the total amount of light in various patches of sky and
estimated how many galaxies would be needed to create that much light.
-
- Estimates put it at 200 billion, maybe even
100 billion galaxies in the visible universe.
So somewhere between 2 trillion galaxies at the top edge and 100 billion
at the lower edge is the number of galaxies in our observable universe.
-
- If you assume that's 3%, at most, of our universe, you can multiply
that range of galaxies to get the total number of galaxies in the universe. If
we're seeing less of the universe than we think, there will be a smaller total
number of galaxies.
-
- We don't actually know the size of the
universe. Astroomy has a ways to go.
-
-
August 8, 2024 UNIVERSE - How
big is it, really? 4533
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