A team of astrophysicists from the University of Copenhagen has come to an important conclusion regarding star populations outside of the Milky Way. This outcome has the potential to change our understanding of a broad range of astronomical phenomena, including the formation of black holes, supernovae and why galaxies die
The appearance of stars in faraway galaxies has been a mystery for as long as people have explored the cosmos. Now, a team of researchers from the Niels Bohr Institute at the University of Copenhagen has disproved prior theories about stars beyond our galaxy in a paper published on 25th May 2022 in The Astrophysical Journal.
Since 1955, it has been presumed that the makeup of stars in other galaxies in the universe is comparable to that of our galaxy’s hundreds of billions of stars, which is a mix of massive, medium mass, and low mass stars.
The team has explored whether the same distribution of stars seen in the Milky Way applies elsewhere using measurements from 140,000 galaxies around the cosmos and a variety of sophisticated models.
But that was not the case. Stars in faraway galaxies are often more massive than those in “close proximity.” The discovery has a significant influence on the understanding of the cosmos.
The mass of stars tells us astronomers a lot. If you change mass, you also change the number of supernovae and black holes that arise out of massive stars. As such, our result means that we will have to revise many of the things we once presumed, because distant galaxies look quite different from our own.
Albert Sneppen, Study First Author and Student, Niels Bohr Institute, University of Copenhagen
Analyzed Light From 140.000 Galaxies
For more than fifty years, scientists assumed that the size and weight of stars in other galaxies were identical to our own since they could never view them via a telescope as they could with our own galaxy’s stars.
Countless billions of light-years separate distant galaxies. As a result, only the brightest stars’ light ever reaches Earth.
This has been a source of frustration for astronomers throughout the world for years, as they have never been able to pinpoint how stars in other galaxies are dispersed, leaving them to think that they are distributed similarly to the stars in the Milky Way.
We have only been able to see the tip of the iceberg and known for a long time that expecting other galaxies to look like our own was not a particularly good assumption to make.
Charles Steinhardt, Study Co-author and Associate Professor, Niels Bohr Institute, University of Copenhagen
Steinhardt added, “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 may open the door for a deeper understanding of galaxy formation and evolution.”
The researchers used the COSMOS catalog, a massive worldwide collection of more than one million observations of light from other galaxies, to evaluate light from 140,000 galaxies. These galaxies can be found everywhere in the universe, from the nearest to the most distant regions, where light has traveled a total of twelve billion years before reaching Earth.
Massive Galaxies Die First
The discovery, according to the experts, will have a wide variety of repercussions. Why galaxies die and stop generating new stars, for example, is still a mystery. According to the current findings, this might be explained by a simple trend.
“Now that we are better able to decode the mass of stars, we can see a new pattern; the least massive galaxies continue to form stars, while the more massive galaxies stop birthing new stars, This suggests a remarkably universal trend in the death of galaxies”, added Sneppen.
The study was carried out at the Cosmic Dawn Center (DAWN), a Danish National Research Foundation-funded international astronomy fundamental research center. The Niels Bohr Institute at the University of Copenhagen and DTU Space at the Technical University of Denmark collaborated on DAWN.
Through observations with the greatest telescopes, as well as theoretical study and simulations, the center is committed to understanding when and how the first galaxies, stars, and black holes originated and developed in the early universe.
Sneppen, A, et al. (2022) Implications of a Temperature-dependent Initial Mass Function. I. Photometric Template Fitting. The Astrophysical Journal doi:10.3847/1538-4357/ac695e.