Why do galaxies die?
Our galaxy is relatively young, and it is still producing stars. Other galaxies have long since stopped doing so, becoming what is known as quiescent, or passive and gas-poor. Now, research published Thursday in the journal Nature explains why this phenomenon happens.
In their paper, experts from the University of Cambridge and the Royal Observatory Edinburgh Institute for Astronomy explain that although the “primary mechanism responsible for quenching star formation in galaxies and transforming them into quiescent and passive systems” is unclear, and in many cases, the cause is linked to something known as “strangulation.”
Strangulation, Science explains, occurs when gas no longer falls into the galaxy, cutting off the supply of materials required in order to form new stars. The authors reached this conclusion after comparing nearly 4,000 star-forming galaxies alongside more than 22,000 that are quiescent.
What are the conditions for a dying galaxy?
They found that galaxies less than twice as massive as the Milky Way with low levels of iron and other heavy elements are no longer producing new stars.
This correlates to the presence of infalling gas, as that gas had little iron content and could dilute the overall abundance in the galaxy. Once the gas is no longer entering the galaxy, the abundance of iron and other heavy elements would increase due to exploding stars, the authors explained.
Their research found that roughly four billion years pass between the halting of infalling gas and the end of star production in those galaxies – a discovery that is supported by independent verification of the stellar age differences found in quiescent and star-forming galaxies, they added.
An exciting discovery
“What kills galaxies is one of the most challenging questions in the past 20 years,” lead author Yingjie Peng, an astronomer at the University of Cambridge, told Discovery News on Thursday. “This is the first conclusive evidence that galaxies are being strangled to death.”
He added that while his team’s research revealed that strangulation is the primary cause of death in galaxies, they still need to better understand the mechanisms responsible for this phenomenon. They believe that it is possible that neighboring galaxies may help deplete the gas supply of star-forming galaxies, and they plan to expand their analysis to include more distant galaxies.
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