The stars are heavier than we thought

Left: best-fit temperature from 10 to 50 K versus analysis time of a sample of 139,535 COSMOS2015 galaxies with S/N > 10 in the V-band (Laigle et al. 2016). At each redshift, the distribution is individually normalized to emphasize the temperature distribution at all redshifts. With an increased redshift, fewer galaxies are adapted to lower temperatures. Right: smoothed mean per boxcar with standard deviation of the best-fit gas temperature at different retrospection times (with mean determined from objects in 2 Gyr age bands and not including galaxies adjusted to the limits of the temperature range). The average temperature increases from ∼28 to ∼36 K from present to 12 Gyr, while the propagation decreases. Credit: The European Journal of Physics E (2022). DOI: 10.1140/epje/s10189-022-00183-5

A team of astrophysicists from the University of Copenhagen has reached a major result concerning the populations of stars beyond the Milky Way. The result could change our understanding of a wide range of astronomical phenomena, including the formation of black holes, supernovae and why galaxies die.

Since humans have been studying the heavens, what stars look like in distant galaxies has remained a mystery. In a study published today in The Astrophysical Journala team of researchers from the Niels Bohr Institute at the University of Copenhagen are challenging previous knowledge about stars beyond our own galaxy.

Since 1955, it has been assumed that the composition of stars in other galaxies in the universe is similar to that of the hundreds of billions of stars in our own – a mixture of massive, medium-mass and low-mass stars. But with the help of observations of 140,000 galaxies across the universe and a wide range of advanced models, the team tested whether the same apparent star distribution in the Milky Way holds elsewhere. The answer is no. Stars in distant galaxies are generally more massive than those in our own. “local neighborhood”. The discovery has a major impact on what we think we know about the universe.

“The mass of stars tells us a lot to astronomers. If you change the mass, you also change the number of supernovae and black holes that emerge from massive stars. As such, our result means that we will have to revise many things. we once assumed, because distant galaxies look very different from ours,” says Albert Sneppen, graduate student at the Niels Bohr Institute and first author of the study.

Analysis of light from 140,000 galaxies

The researchers assumed that the size and weight of the stars of other galaxies were similar to ours for more than fifty years, for the simple reason that they were unable to observe them through a telescope, as they could with the stars of our own galaxy.

Distant galaxies are billions of light years away. As a result, only the light from their most powerful stars reaches Earth. This has puzzled researchers around the world for years, as they have never been able to accurately clarify the distribution of stars in other galaxies, an uncertainty that has forced them to believe they were distributed. much like the stars in our Milky Way.

“We were only able to see the tip of the iceberg, and we’ve known for a long time that expecting other galaxies to look like ours wasn’t a particularly good guess to make. However, no one has ever been able to prove that other galaxies form different star populations. This study allowed us to do just that, which could open the door to a deeper understanding of how galaxies form and evolve,” says Associate Professor Charles Steinhardt, co-author of the study.

In the study, the researchers analyzed light from 140,000 galaxies using the COSMOS Catalog, a large international database of more than a million light observations from other galaxies. These galaxies are distributed from the nearest to the farthest reaches of the universe, from where light has traveled twelve billion years before being observable on Earth.

Massive galaxies die first

According to the researchers, the new discovery will have a wide range of implications. For example, we still don’t know why galaxies die and stop forming new stars. The new result suggests that this could be explained by a simple trend.

“Now that we are better able to decode the mass of stars, we can see a new pattern; less massive galaxies continue to form stars, while more massive galaxies stop giving birth to new stars. This suggests a remarkably universal trend in star death. galaxies,” Sneppen concludes.