Analysing stars’ mass reveals distant galaxy discovery

Astrophysicists at the University of Copenhagen have made a discovery about distant galaxies by analysing star populations beyond the Milky Way.

For as long as humans have studied astronomy, how stars appear in distant galaxies has remained a mystery. In a study published in The Astrophysical Journal, a team of researchers at the University of Copenhagen’s Niels Bohr Institute are changing previous understandings of stars through a novel distant galaxy discovery.

Distant galaxy discovery

Since 1955, researchers assumed that the size and weight of stars in other galaxies are like that of our own for the simple reason that they were unable to observe them through a telescope, as they could with the stars of our own galaxy. It was believed that there is a mixture of massive, medium mass, and low mass stars in distant galaxies.

However, with the help of observations from 140,000 galaxies across the Universe and a wide range of advanced models, astrophysicists have tested whether the same distribution of stars visible in the Milky Way applies elsewhere.

The University of Copenhagen scientists believe not. Stars in distant galaxies are typically more massive than those in our ‘local neighbourhood.’ The finding will have a major impact on what we think we know about the universe.

“The mass of stars tells astronomers a lot,” explained Albert Sneppen, a Graduate Student at the Niels Bohr Institute and first author of the study. “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.”

Analysing the characteristics of stars in distant galaxies

Distant galaxies are billions of light-years away. As a result, only light from their most powerful stars ever reaches Earth. This has been a huge obstacle for researchers world-wide for years, as they were unable to accurately clarify how stars in other galaxies were distributed, an uncertainty that forced them to believe that they were distributed much like the stars in our 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,” explained Associate Professor Charles Steinhardt, a co-author of the study. “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.”

Investigating light from 140,000 galaxies

In the study, the researchers analysed light from 140,000 galaxies using the COSMOS catalogue, a large international database of more than one million observations of light from other galaxies. These galaxies are distributed from the nearest to farthest reaches of the Universe, from which light has travelled twelve billion years before being observable on Earth.

According to researchers, this new discovery will have a wide range of implications. For example, it remains unresolved why galaxies die and stop forming new stars. The new result suggests that this might be explained by a simple trend.

Massive galaxies die first

“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,” concluded Albert Sneppen.

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

The centre is dedicated to understanding when and how the first galaxies, stars, and black holes formed and evolved in the early Universe, through observations utilising the largest telescopes along with theoretical work and simulations.

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