Astronomers have known there are two main classes of galaxies for some time now. Close to half of the known galaxies are gas-rich galaxies where stars form, and the other half are dead, gas-deprived galaxies where stars no longer form, but why some form stars and others don’t was not really understood.
A new study led by Yingjie Peng, an astronomer at the University of Cambridge in England, sheds new light on the subject, and suggests that the “:dead” galaxies are strangling because of too many heavy metals. The new research was published in the May 14th edition of the academic journal Nature.
More on metals and strangulation of galaxies
The new research determined that dead galaxies had greater amounts of metals than live ones did. Peng noted that this is consistent with how strangulation would cause galaxies to evolve over time.
After a galaxy’s gas supply is cut off, it still has some gas that can be used to form stars. These stars can then form elements heavier than hydrogen and helium. On the other hand, in galaxies where gas is suddenly removed, star formation stops abruptly, leading to less metals.
The models developed by the astronomers indicate that strangulation takes close to 4 billion years to end star formation. Of note, this matches the age difference between star-forming, live and dead galaxies.
The strangulation theory works for galaxies up to 100 billion times heavier than the sun, which represent over 95% of all galaxies. For the largest galaxies, the evidence of strangulation was not conclusive..
Researchers still need to get a better grip on the mechanism that causes strangulation. One possibility nearby galaxies may deplete a star-forming galaxy’s gas supply in the early stages of formation, Peng said
The researchers studied 26,000 relatively nearby galaxies, and future research will examine more distant galaxies, which provide a picture of what the universe was really like when it was young. Additional research will allow researchers to come to a better understanding of how galaxies form and evolve, Peng noted.
He continued: “We have many forthcoming powerful instruments, such as the Multi-Object Optical and Near-infrared Spectrograph (MOONS), and telescopes such as the space-based James Webb Space Telescope, which will make our research plan feasible in the next few years.”