By now we know that the vast majority of galaxies have supermassive black holes in their cores. These galactic behemoths generate some energetic phenomena, especially when matter falls onto their accretion disks and event horizons. Often, the energy generated by active galactic nuclei (where these rambunctious black holes reside), will regulate the star formation processes in their host galaxy.
Now, in a new study published in the journal Monthly Notices of the Royal Astronomical Society, researchers believe that they’ve found the reason why maturing galaxies seem to “switch off” star formation all together.
“When you look into the past history of the universe, you see these galaxies building stars,” said Tobias Marriage, of Johns Hopkins University and co-lead author of the study. “At some point, they stop forming stars and the question is: Why? Basically, these active black holes give a reason for why stars stop forming in the universe.”
Marriage and his colleagues used an established method for studying large clusters of galaxies and applying it to single galaxies. By doing this, they discovered that supermassive black holes are driving “radio-frequency feedback,” which is heating up the galaxies, preventing interstellar gases from cooling, clumping and forming new stars.
In short, massive black holes, at a certain age, act like a switch and are snuffing out star formation before it can even take hold.
Normally, the Sunyaev–Zel’dovich (SZ) effect signature is used to study how the primordial cosmic microwave background radiation (the ‘echo’ of the Big Bang) interacts with the electrons inside interstellar gases locked in clusters of hundreds of galaxies. But for the first time, this method has been down-scaled to gauge the interstellar environment of single galaxies.
“The SZ is usually used to study clusters of hundreds of galaxies but the galaxies we’re looking for are much smaller and have just a companion or two,” said Megan Gralla, also of Johns Hopkins.
“What we’re doing is asking a different question than what has been previously asked,” Gralla said. “We’re using a technique that’s been around for some time and that researchers have been very successful with, and we’re using it to answer a totally different question in a totally different subfield of astronomy.”
So, while studying the SZ effect signature in galaxies, the researchers found that all the galaxies displaying radio-frequency feedback coincided with galaxies that also lacked signs of star formation. It just so happened that these particular galaxies were large and mature elliptical galaxies, where their heated interstellar gas was prevented from cooling down.
“If gas is kept hot, it can’t collapse,” said Marriage. If the gas cannot collapse, no new stars can form.
Read more at Discovery News
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