The universe is a very big place full of awesome wonders that no human will ever see in its entirety, and that’s what makes it so humbling. Just when we humans think we have something figured out about the universe, it throws us a curveball. We once thought Earth was the center of the universe, known as the geocentric model. Despite going uncontested for 1400 years, this model was eventually proven to be wrong, as Nicolaus Copernicus helped establish the heliocentric (sun-centered) model in the 16th century. Even with this, it took until 1923 to discover that our Milky Way was not the only galaxy in the universe, which is just one of two trillion galaxies in the observable universe. But what kinds of stars exist in those galaxies? Are they similar to our own Sun, or do they vary in size like the rest of our stars in our Milky Way?
In a recent study published in The Astrophysical Journal, a team of researchers at the University of Copenhagen's Niels Bohr Institute is doing away with previous understandings of stars beyond our own galaxy. With the help of observations from 140,000 galaxies across the universe and a wide range of advanced models, the team has tested whether the same distribution of stars apparent in the Milky Way applies elsewhere. The answer is no. Stars in distant galaxies are typically more massive than those in our "local neighborhood." The finding has a major impact on what we think we know about the universe.
"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'll have to revise many of the things we once presumed, because distant galaxies look quite different from our own," says Albert Sneppen, a graduate student at the Niels Bohr Institute and first author of the study.
Researchers assumed that the size and weight of stars in other galaxies was similar to our own 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 light from their most powerful stars ever reaches Earth. This has been a headache for researchers around the world for years, as they could never 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've 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. 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," says Associate Professor Charles Steinhardt, a 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 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 traveled a full twelve billion years before being observable on Earth.
The results demonstrate that stars in distant galaxies are typically more massive than those in our local neighborhoods, and that the farther away the researchers look, the more massive the average stars become.
More massive stars don’t necessarily mean better chances for life, however, as larger stars have a much shorter lifespan than stars like our sun. While stars like our sun live about 10 billion years, stars that are 20 times as big as our sun only live about 10 million years. While the Earth is approximately 4.5 billion years old, the first signs of life didn’t take place for another 800 million years. This doesn’t bode well for finding life on planets orbiting larger stars.
What other secrets will we unlock about other galaxies? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!