- 4181 - BIG BANG - how many galaxies formed? - When scientists viewed the James Webb Space Telescope’s (JWST) first images of the universe’s earliest galaxies, they were shocked. The young galaxies appeared too bright, too massive and too mature to have formed so soon after the Big Bang. It would be like an infant growing into an adult within just a couple years.
--------------------- 4181 - BIG BANG - how many galaxies formed?
- The startling discovery
even caused some physicists to question the standard model of cosmology,
wondering whether or not it should be upended.
Using new simulations astrophysicists now have discovered that these
galaxies likely are not so massive after all. Although a galaxy’s brightness is
typically determined by its mass, the new findings suggest that less massive
galaxies can glow just as brightly from irregular, brilliant bursts of star
formation.
-
- Not only does this
finding explain why young galaxies appear deceptively massive, it also fits
within the standard model of cosmology.
The discovery of these galaxies was a big surprise because they were
substantially brighter than anticipated.
-
- Typically, a galaxy
is bright because it’s big. But because these galaxies formed at cosmic dawn,
not enough time has passed since the Big Bang. How could these massive galaxies
assemble so quickly? Our simulations show that galaxies have no problem forming
this brightness by cosmic dawn.
-
- The key is to
reproduce a sufficient amount of light in a system within a short amount of
time. That can happen either because the
system is really massive or because it has the ability to produce a lot of
light quickly. In the latter case, a system doesn’t need to be that massive. If
star formation happens in bursts, it will emit flashes of light. That is why we
see several very bright galaxies.
-
- A period that
lasted from roughly 100 million years to 1 billion years after the Big Bang,
“cosmic dawn” is marked by the formation of the universe’s first stars and
galaxies. Before the JWST launched into space, astronomers knew very little
about this ancient time period.
-
- The JWST brought
us a lot of knowledge about cosmic dawn.
They used advanced computer simulations to model how galaxies formed
right after the Big Bang. The simulations produced cosmic dawn galaxies that
were just as bright as those observed by the JWST.
-
- The “FIRE
simulations” combine astrophysical theory and advanced algorithms to model
galaxy formation. The models enable researchers to probe how galaxies form,
grow and change shape, while accounting for energy, mass, momentum and chemical
elements returned from stars.
-
- At cosmic dawn,
they discovered that stars formed in bursts, a concept known as “bursty star
formation.” In massive galaxies like the Milky Way, stars form at a steady
rate, with the numbers of stars gradually increasing over time. But so-called
“bursty star formation” occurs when stars form in an alternating pattern, many
stars at once, followed by millions of years of very few new stars and then
many stars again.
-
- Bursty star
formation is especially common in low-mass galaxies. The details of why this happens are still the
subject of ongoing research. But what we think happens is that a burst of stars
form, then a few million years later, those stars explode as supernovae.
-
- The gas gets
kicked out and then falls back in to form new stars, driving the cycle of star
formation. But when galaxies get massive enough, they have much stronger
gravity. When supernovae explode, they are not strong enough to eject gas from
the system. The gravity holds the galaxy together and brings it into a steady
state.
-
- The simulations
also were able to produce the same abundance of bright galaxies as the JWST
revealed. The number of bright galaxies
predicted by simulations matches the number of observed bright galaxies.
-
- Most of the light
in a galaxy comes from the most massive stars.
Because more massive stars burn at a higher speed, they are shorter
lived. They rapidly use up their fuel in nuclear reactions. So, the brightness
of a galaxy is more directly related to how many stars it has formed in the
last few million years than the mass of the galaxy as a whole.
-
October 7, 2023 BIG BANG -
how many galaxies formed 4181
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