After analyzing the chemical elements in the faintest known galaxy, called Segue 1, researchers determined that it may be a fossil from an early universe.
The early formation of galaxies after the Big Bang has always remained a fascinating topic to astronomers. To gain a better understanding of this process, researchers have analyzed the chemical composition of stars in the Milky Way and other nearby galaxies. During one such analysis, researches from the Carnegie Institute For Science unraveled the uniquely ancient composition of Segue 1, a nearby galaxy.
Star formation is a very interesting topic. They form from gas clouds and their chemical composition is similar to that of the galactic gas from which they are born. Million years after the stars start burning, they burst to form what is known as a supernova, feedings nearby gas clouds with new chemical elements they may have developed over the years.
Previous studies have established that the oldest stars are mainly composed of hydrogen and helium because they formed much before supernovae developed heavier elements. This process is called cyclical. However, Segue 1 is different. Researchers found that this galaxy's star formation ended at a time, which is generally the early stage development for other galaxies. Its tiny size may be responsible for this.
"Our work suggests that Segue 1 is the least chemically evolved galaxy known," lead author Josh Simon said in a statement. "After the initial few supernova explosions, it appears that only a single generation of new stars were formed, and then for the last 13 billion years the galaxy has not been creating stars."
Owing to the fact that Segue 1 has remained in one stage for a very long time, it provides researcher with insight into early universe, after the Big Bang. Other galaxies have undergone multiple supernova explosions since their formation.
During the first supernova explosion, elements like magnesium, silicon, and calcium are produced. Iron is produced in later explosions. The low level of iron in Segue 1 is evidence suggesting its star formation must have stopped before any of the iron-forming supernovae occurred. Researchers also noticed that very heavy elements like barium and strontium are nearly absent in the stars of this galaxy.
"The heaviest elements in this galaxy are at the lowest levels ever found," said Anna Frebel of the Massachusetts Institute of Technology, the leader of the team. "This gives us clues about what those first supernovae looked like. Having found such a fossil galaxy is of enormous importance to astronomy, because it provides a new window into the first galaxies."
Segue 1 has only about a thousand stars with only seven of them in the red giant phase of their lives, making them bright enough to be detected by modern telescopes. Three of the seven red giants have heavy element in levels 3,000 times lower than that of the Sun, highlighting the primitive nature of the galaxy. The puny size of the galaxy makes it all the more difficult for researchers to study individual stars in it.
The study was funded by the NSF and the Southern California Center for Galaxy Evolution and published online in Astrophysical Journal.
