A census of 140,000 galaxies reveals a surprising fact about their stars

(ORDO NEWS) — How many stars of what type live in other galaxies? This seems like a simple question, but it’s notoriously difficult to determine because it’s very difficult for astronomers to estimate the stellar population in distant galaxies.

Now a team of astronomers has completed a census of over 140,000 galaxies and found that distant galaxies tend to have heavier stars.

Star census

While astronomers don’t have a complete census of all the hundreds of billions of stars in the Milky Way galaxy, they have taken enough samples to get a pretty good idea of ​​the population.

We know approximately how many small dwarf stars there are, how many medium-sized stars like the Sun are there. there are and how many giant ones exist.

But repeating this exercise for other galaxies is extremely difficult. Most galaxies are simply too far away to identify and measure the individual stars within them.

We only see their brighter, heavier stars, and we have to guess about populations of smaller ones.

Typically, astronomers simply assume that the demographics of a distant galaxy roughly match what we see in the Milky Way, because, on average, galaxies shouldn’t be very different from one another.

Recently, a team of astronomers used the COSMOS catalog to study 140,000 individual galaxies, developing methods to estimate the number of stars in each.

The study was conducted at the Space Dawn Center (DAWN), an international center for basic research in astronomy, supported by the Danish National Research Foundation. DAWN is a collaboration between the Niels Bohr Institute of the University of Copenhagen and DTU Space of the Technical University of Denmark.

Future fate of heavier galaxies

“We could only see the tip of the iceberg and knew for a long time that expecting other galaxies to look like our own was not a particularly good guess.

However, no one has ever been able to prove that other galaxies form different populations of stars. This study has allowed us to do just that, which could open the door to a deeper understanding of galaxy formation and evolution,” says Associate Professor Charles Steinhardt. study co-author.

The team found that, on average, more distant galaxies tend to have larger stars than the Milky Way. On the other hand, nearby galaxies were relatively similar to ours.

“The mass of the stars tells us astronomers a lot. If you change the mass, you also change the number of supernovae and black holes that emerge from them. massive stars.

So our result means we’ll have to rethink a lot of the things we once thought, because distant galaxies look completely different than ours,” says Albert Sneppen, a PhD student at the Niels Bohr Institute and first author of the study.

This work has several important implications.

First, astronomers can no longer assume a homogeneous population of stars by looking at distant galaxies, which represent the youngest galaxies. appear in the universe. It also forces us to rethink how galaxies evolve over billions of years.

“Now that we better decipher the mass of stars, we can see a new pattern: the smallest mass galaxies continue to form stars. , while more massive galaxies stop producing new stars. This points to a remarkably universal trend towards galaxy death,” Snappen concludes.

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