- 4178 - EARLIEST GALAXIES - why are they so bright? 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.
--------------- 4178 - EARLIEST GALAXIES - why are they so bright?
- 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, a Northwestern
University-led team of astrophysicists now has 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? Simulations show
that galaxies have no problem forming this brightness by cosmic dawn.
-
- 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.
-
- Prior to JWST, most
of our knowledge about the early universe was speculation based on data from
very few sources. With the huge increase in observing power, we can see
physical details about the galaxies and use that solid observational evidence
to study the physics to understand what’s happening.
-
- Advanced
computer simulations produced cosmic
dawn galaxies that were just as bright as those observed by the JWST. The
simulations are part of the Feedback of Relativistic Environments(FIRE)
project. The new study includes collaborators from the
Flatiron Institute’s Center for Computational Astrophysics, Massachusetts
Institute of Technology and University of California, Davis.
-
- 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.
-
- 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. 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.
-
- 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 5, 2023 EARLIEST
GALAXIES - why are they so bright? 4178
------------------------------------------------------------------------------------------
-------- Comments
appreciated and Pass it on to whomever is interested. ---
--- Some reviews are
at: -------------- http://jdetrick.blogspot.com -----
-- email feedback,
corrections, request for copies or Index of all reviews
--- to: ------
jamesdetrick@comcast.net
------ “Jim Detrick” -----------
--------------------- ---
Thursday, October 5, 2023 ---------------------------------
No comments:
Post a Comment