Name: Where Do Galaxies Come From?
Uploaded: 2021-10-08T17:50:30.000Z
Duration: 2 min 55 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

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

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.