Most things in the universe happen too slowly for us to see them happening. Stars like the
sun take tens of millions of years to form, and hundreds of millions of years to orbit
their galaxies; colliding galaxies take billions of years to merge. And yet we have a pretty
decent understanding of how all these things happen, because there are so many of them
in the observable universe that we can look out and see different versions of similar
events happening in different places, and because light takes time to get here we see
places at different distances at different times thoughout the history of the universe,
and from all that we can piece together an understanding of how stars are born and how
they die, how galaxies develop and interact, and so on. It’s kind of like if you only
had ten minutes to study how humans grow: you couldn’t see any one person grow very much
in that time, but by looking at humans of different ages all around the world, you can
get a pretty good picture of what a human life looks like.
However, the very first galaxies to ever form were so small and dim that we don't have nearly
as good an idea of how baby galaxies are born as we do about how they behave and interact
later in life.
Our current understanding is that in the early universe, before any stars had formed, everything
was just spread-out gas and a lot of dark matter. Gravity would have caused slightly
denser areas of dark matter to attract into clumps, pulling in bits of gas until they
were dense enough on their own to gravitationally collapse and start thermonuclear fusion. A
star. Many stars. Clusters of stars and their associated dark matter attracted together
and merged, and then those clustered-clusters clustered together, eventually forming the
most distant (and longest-ago) galaxies we see today.
But we don’t know exactly how soon after the big bang the clumps of dark matter and
gas formed; or when during the process of clumping and clustering the first stars ignited;
or if there was a minimum dark-matter-clump size necessary to attract enough gas to form
stars; or if the very first star clusters came together to form galaxies at all – they
might have been so small and fragile they were blown apart when their own stars went
supernova and the first galaxies may have actually formed from a second round of clumping
of gas and dark matter as well as dust from the explosions.
To be honest, we don't even have a good enough definition of what a galaxy is to know when
to stop calling something a cluster of stars and when to start calling it a galaxy.
What we do know is that today we have bajillions of galaxies in our universe, none of which
existed 13.8 billion years ago, so somewhere in between they must all have been babies.
Big gassy babies surrounded by clumps of dark matter.
This video was made with the support of NASA’s James Webb Space Telescope and the Space Telescope
Science Institute. The James Webb Space Telescope is especially sensitive to the infrared wavelengths
that light from baby galaxies gets stretched to by the time it arrives in our solar system,
so astronomers are excitedly looking forward to using the JWST to learn more about the
very first stars and galaxies that ever formed in the universe.