We think of galaxies as ancient. Our galaxy, Milky WayIt was formed 13.6 billion years ago and James Webb Space Telescope allowed us to look back some of the first galaxies in the early universe. So are galaxies still being born today?
This is a fun question to tackle because it gives us the opportunity to delve deeper into a complex, intricate, and beautiful process. galaxy formationLet’s take a look at the possibilities.
First answer: No
Galaxies are fairly easy to define. They are large collections of stars, gas, and dark matter. They are vastly different from each other; a typical galaxy is about 100,000 light-years across, with the typical distance between galaxies being about 1 million light-years.
Sometimes galaxies cluster together or clump together, but with a few exceptions, we can often tell one galaxy apart from another. They are like towns in the countryside: the distance between towns is greater than the towns themselves, so they are easy to spot and identify. Sometimes towns are side by side, and sometimes a sprawling city swallows its neighbors. But in general, a town is just a town.
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But defining the beginning of a galaxy is a different matter. Galaxies emerged in the early universe through a gradual process, starting from the first seconds of the universe. Big Bang. At that time, tiny pockets of higher-than-average density appeared and grew steadily over the next few hundred million years. At first, only dark matter could flow in because the regular matter was busy mixing in. But when the pockets of dark matter grew large enough, they pulled in the surrounding regular matter.
As regular matter gathered, it was compressed, broken apart, and gave off light into the primary matter. starsThese protogalaxies continued to consume more gas, merge with their neighbors, and become the fully formed galaxies we see today.
So, in many senses, new galaxies are not emerging today. The process of building them — seeding as tiny differences in density or the initial accretion of dark matter — is over and done with, an action that happened in the old cosmos and never happened again. There are no more protogalaxies in the present-day universe — no more clouds of gas waiting for their chance to compress and create a new galaxy.
When it comes to galaxies, what we see is what we get.
Second answer: yes
But this is just one way to describe the beginning of a galaxy. We can also look at another important step: the first stars appearedGoing back to the city analogy, there is a difference between when a city is first planned (outlined with landmarks and survey lines) and when the first people start moving into the city.
If we focus solely on star formation, we see that it’s an ongoing process that continues even in the modern universe. In recent years, astronomers have developed a detailed understanding of a measure called the stellar mass function. It’s a basic demographic census that maps how many stars shine in each galaxy — or, in other words, how much mass each galaxy had at different epochs in the universe.
Stars make up only a small percentage of a galaxy’s mass; the rest goes to dark matter and random clumps of gas. But stars are what make a galaxy a galaxy, and they’re much more easily observed than any other galactic component.
In new studies sampling galaxies across the universe, astronomers have recently discovered that the stellar mass function is increasing overall. This means that there are more small galaxies, medium-sized galaxies, and large galaxies than there were billions of years ago.
New small galaxies do not arise from protogalaxies in dark matter seeds; they are already existing clumps of matter where star formation has just begun. Larger galaxies, on the other hand, are driven mostly by the continued merger of smaller galaxies.
It won’t last forever
So, at least in a significant way, new galaxies continue to appear on the cosmic stage as they light up with new rounds of star formation. They’ve always been there, hanging there for billions of years, but now they’re making themselves visible. This process works because star formation is incredibly inefficient. Most of the gas in a galaxy never turns into stars, and can go on for very long periods of time without using up much material — and it can take a very long time indeed for a galaxy to get started in the first place.
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But unfortunately, the party won’t last forever. The problem is, it’s just The universe is expandingbut its expansion is accelerating — this effect is dark energyAlthough astronomers still don’t understand what drives dark energy, they can observe its effects on the rest of the universe: It’s messing everything up.
As the universe ages, it becomes increasingly difficult for material to clump together to form new galaxies and sustain star formation. In fact, the peak of star formation passed billions of years ago. While new galaxies continue to light up, the rate of their emergence is slowing, with fewer new galaxies emerging each year.
We still have plenty of time; galaxies will continue to form stars for hundreds of billions of years to come; but we should still enjoy the party.