We consider the galaxy to be ancient. Our galaxy, milky wayIt was formed 13.6 billion years ago. James Webb Space Telescope It gave me an opportunity to look back on the past. Some of the first galaxies In the early universe. But are galaxies still being born today?
This is a fun question to tackle because it allows you to delve into a messy, complex, and beautiful process. Galaxy formationLet’s look at the possibilities.
First answer: No
Galaxy Galaxies are easy to identify. They are large collections of stars, gas, and dark matter. Galaxies vary greatly from one another. A typical galaxy has a diameter of about 100,000 light-years, while the distance between galaxies is usually about 1 million light-years.
Galaxies sometimes merge or cluster together in clusters, but with a few exceptions, galaxies are largely distinct. Galaxies are like towns in the countryside: the distances between the towns are greater than the towns themselves, making them easier to find and distinguish. Sometimes towns run into one another, and sometimes sprawling cities engulf their neighbors. But by and large, a town is just a town.
But defining the beginning of galaxies is another matter: galaxies came into being in the early universe through a step-by-step process that stretches back to the first seconds of the Moon. big bangAt that time, a small mass of higher density than average appeared and grew steadily over the next several hundred million years. Dark matter Normal matter was busy entangling itself with itself, making it nearly impossible for dark matter to flow in. But when a clump of dark matter got big enough, it started to pull in the normal matter around it.
When ordinary matter comes together, it is compressed, fragmented, and the first PerformerThese protogalaxies consumed more gas and grew by merging with neighboring galaxies until they became the complete galaxies we see today.
So, in many senses, new galaxies are not emerging today. The process of galaxy formation – the process by which galaxies form as initial collections of tiny differences in density and dark matter – is over, it happened in the ancient universe, and it will never happen again. There are no more protogalaxies in the current universe, which means there are no more gas clouds waiting for the opportunity to compress and form new galaxies.
When it comes to galaxies, what we see is what we see.
Second answer: Yes
But this is only one way of defining the beginning of the galaxy. Let’s look at another important step. The appearance of the first starsReturning to our city analogy, there is a difference between when a city is first planned – its outline defined by boundary markers and survey lines – and when the first people begin to live there.
If we focus just on star formation, we see that this is an ongoing process that continues in the modern universe. In recent years, astronomers have developed a detailed understanding of a measure called the stellar mass function, a fundamental demographic that maps how many stars are shining in each galaxy. In other words, it shows how much mass has existed in the form of stars within each galaxy at different epochs in the universe.
Stars make up only a tiny fraction of a galaxy’s mass — the rest is dark matter and random clumps of gas — but they’re what make a galaxy a galaxy, and they’re much easier to observe than other components of galaxies.
In a new survey sampling galaxies across the universe, astronomers recently discovered that the stellar mass function is increasing overall, meaning there are more small, medium, and large galaxies than there were billions of years ago.
New dwarf galaxies are not protogalaxies born from seeds of dark matter, but are clumps of pre-existing material that have just begun to form stars, while large galaxies are born primarily through the ongoing merger of dwarf galaxies.
It won’t last forever
This means that, in at least one important respect, new galaxies keep appearing on the cosmic stage, sparkling with new cycles of star formation. They’ve always been there, they’ve been there for billions of years, but only now are they becoming visible. This process is possible because star formation is incredibly inefficient: most of the gas in galaxies never turns into stars, and it happens over very long periods of time without consuming much material, and it takes a very long time for galaxies to even get going in the first place.
But sadly, the party can’t last forever. The expansion of the universeBut the expansion is accelerating. Dark EnergyAstronomers don’t yet understand what drives dark energy, but they can observe its effect on the rest of the universe: it spreads everything out.
As the Universe gets older, it becomes harder and harder for matter to come together to form new galaxies and continue forming stars. In fact, the peak of star formation passed billions of years ago. New galaxies continue to get brighter, but the rate at which they appear is declining, with fewer and fewer new galaxies appearing 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 while it lasts.
