They are formed by a mysterious phenomenon known as “galactic warming.”
Over the last few billion years, a large number of dormant galaxies have been turned into old deserts completely free of fresh young stars. It is a mysterious process known as “galactic warming,” where the gas in these galaxies is kept too hot and energetic to form stars.
Yesterday (May 26), astronomers from the Sloan Digital Sky Survey (SDSS) announced the discovery of a new class of galaxies called “red geysers.” These galaxies contain supermassive black holes at their center, with winds that are powerful enough to keep dormant galaxies inactive.
The name red geyser was chosen because the wind outbursts resemble eruptions of a geyser, and the inability to form new stars leaves the galaxy with only old red dwarfs, which have a lifespan of 6 to 12 trillion years.
“We knew that there had to be a way to prevent star formation in these galaxies, and now we have a good idea of what it is,” Edmond Cheung, the lead author of the study published today in the journal Nature, said in an SDSS press release.
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Cheung, an astronomer at the University of Tokyo’s Kavli Institute for the Physics and Mathematics of the Universe, along with an international team of astronomers, were studying numerous galaxies when they spotted a supermassive black hole blasting winds at the cold gas in its host galaxy. The galaxy has been named Akira.
“Galaxies start out as star-making machines with a simple recipe: gas plus gravity equals stars,” said Kevin Bundy, co-author of the study and principal investigator. “Here we have a galaxy that has everything it needs to form new stars, but is dormant. Why is that?”
Astronomers suspected that supermassive black holes found at the center of many galaxies played a major role, but there was little evidence — it is extremely difficult to map the internal structure and motions of gas and stars throughout the galaxy.
“If we looked just at the center of the galaxy like we used to, we could have learned about the central black hole, but we would have missed the story of how it affects the rest of the galaxy,” Cheung explained. “Another reason is that the wind from supermassive black holes comes and goes quickly, so catching the wind red-handed is hard.”
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So how did the team capture the whole story? By using SDSS’s new Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. It was recently added to the Sloan Foundation Telescope and is capable of capturing quick changes in galaxies, which is how the team found Akira.
Akira is pulling gas away from a companion galaxy named Tetsuo, which is fueling Akira’s supermassive black hole winds. These winds are the reason that Akira is currently a red geyser galaxy.
“You can think of these winds as super-heating the atmospheres of galaxies,” Cheung said. “As soon as any gas starts to cool, it gets blasted by this wind, like water droplets turning to steam.”
The team thinks that this phenomenon is actually quite common in dormant galaxies. In fact, our own Milky Way Galaxy, which has a dormant supermassive black hole (Sagittarius A*) with its own ultra-fast winds, may not be safe from this galactic warming. Billions of years from now, Sagittarius A* may start turning our galaxy into a red geyser.
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