We think galaxies are old. Our galaxy, milky wayFormed 13.6 billion years ago, James Webb Space Telescope It allowed us to look back. Some of the first galaxies At the beginning of the universe. But are galaxies still being born today?
It’s a fun question to answer because it allows us to delve into the messy, complex, and beautiful process. galaxy formationLet’s take a look at the possibilities.
First answer: No
Galaxies Galaxies are pretty easy to recognize. They are large collections of stars, gas, and dark matter. They vary greatly from one another; a typical galaxy is about 100,000 light-years across, while the typical distance between galaxies is about a million light-years.
Sometimes galaxies merge or cluster together, but with few exceptions, we can pretty much tell one galaxy apart from another. It’s like towns in the countryside: the distance between the towns is greater than the towns themselves, so they’re easier to spot and identify. Sometimes towns are clustered side by side, and sometimes a sprawling city swallows up its neighbors. But for the most part, a town is just a town.
Related: Did black holes or giant galaxies come first? The James Webb Space Telescope may have a surprising answer
But determining the beginning of a galaxy is a different matter. Galaxies in the early universe arose in a gradual process that began in the first second of the universe’s life. the great explosionAt that time, small pockets of higher than average density appeared and grew steadily over the next hundreds of millions of years. At first, it was just Dark matter Dark matter could have flowed inward, as ordinary matter was busy entangled with itself. But once the dark matter pockets got big enough, they attracted the surrounding ordinary matter.
When the ordinary matter gathered, it compressed and crumbled and gave light to the first part. starsThese early galaxies continued to consume more gas, merge with their neighbors, and grow into the full-fledged galaxies we see today.
So new galaxies are by no means emerging today. The process of galaxy building — seeding them with tiny density differences or gathering dark matter in the first place — that took place in the early universe is over and will not happen again. There are no more primordial galaxies — no clouds of gas waiting to be compressed into a new galaxy — in the present universe.
When it comes to galaxies, what we see is what we get.
Second answer: Yes
But that’s just one way to pinpoint the beginning of the galaxy. We can also look at another pivotal step: The first stars appearReturning to the city analogy, there is a difference between when a city is first planned—marked with boundary markers and survey lines—and when the first people begin to move in.
If we focus solely on star formation, we see that this is an ongoing process even in the modern universe. In recent years, astronomers have built a detailed understanding of a measure called the stellar mass function. This is a basic demographic census that maps the number of bright stars in each galaxy—in other words, the amount of mass in the form of stars within each galaxy at different epochs in the universe.
Stars make up only a tiny percentage of a galaxy’s mass; the rest goes to dark matter and random clumps of gas. However, stars are what make a galaxy what it is, and they are much easier to observe than any other galactic component.
Thanks to new surveys of galaxies across the universe, astronomers have recently discovered that the stellar mass function is increasing steadily. This means that there are more small, medium and large galaxies than there were billions of years ago.
New small galaxies do not arise from the seed of dark matter primordia; rather, they are clumps of matter that are already there and are beginning to form stars. Larger galaxies, on the other hand, are mostly created by the ongoing merger of smaller galaxies.
It won’t last forever
And so, in at least one important way, new galaxies continue to appear on the cosmic scene, illuminated by new rounds of star formation. They’ve always been there, hanging around for billions of years, but they’re just now making themselves visible. This process works because star formation is incredibly inefficient. Most of the gas inside a galaxy will never turn into stars, and that can go on for very long periods without using up much material—and it can take a really long time to get a galaxy started in the first place.
But unfortunately the party will not last forever. The problem is not only that The universe is expandingBut its expansion is accelerating – an effect known as Dark energyAlthough astronomers still don’t understand what drives dark energy, they can observe its effects on the rest of the universe: it pervades everything.
As the universe ages, it becomes harder for matter to clump together to form new galaxies and drive the ongoing star formation process. In fact, the peak of star formation ended billions of years ago. While new galaxies continue to appear, the rate at which they appear is slowing, with fewer and fewer new galaxies appearing each year.
We still have plenty of time — galaxies will continue forming stars for hundreds of billions of years to come — but we have to enjoy the party while it lasts.
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