(ORDO NEWS) — The Milky Way galaxy is not very active when it comes to galaxies. About three or four Suns of new stars are formed annually over the entire area of its spiral body, and stars of different ages can be found everywhere.
But there are galaxies even quieter – elliptical galaxies, in which the formation of stars stopped a long time ago. No or very few stars younger than a certain age have been found in these galaxies, which suggests that at some point star formation abruptly stopped, and the galaxy slowly faded over the centuries, star by star.
How exactly star formation is turned off in these smooth, nearly featureless galaxies remains a mystery, but astronomers believe it has something to do with the supermassive black holes that lie at the center of every galaxy.
Now, an international team of astronomers, led by Kei Ito of the SOKENDAI Graduate University for Advanced Study in Japan, has peered into the early universe to find out if this is the case.
Using some of the most powerful telescopes in the world, they collected data across multiple wavelengths to identify galaxies whose light traveled across the space-time chasm in 9.5 to 12.5 billion years – ancient galaxies similar to the elliptical galaxies closer to us in space and time, for which star formation is on the verge of extinction.
The first step was to use optical and infrared data to identify galaxies in which star formation continues and those in which star formation has ceased.
The next step was to use X-ray and radio data to detect the activity of supermassive black holes. This is the mechanism by which, according to astronomers, star formation can be quenched.
When a supermassive black hole is active, it absorbs massive amounts of matter from the space around it. This process is erratic and tumultuous, giving rise to what is collectively known as “feedback”.
We all know that nothing can appear beyond the event horizon of a black hole, but the space around it is a completely different matter.
Material swirls around a black hole like water around a drain; gravity and friction give rise to intense radiation that flares up throughout the universe.
Another form of feedback is jets escaping from the polar regions of a black hole. Material outside the event horizon is believed to be accelerated along the black hole’s external magnetic field and then ejected from the poles in powerful, focused plasma jets that travel at a significant fraction of the speed of light.
Finally, active supermassive black holes generate intense winds that spread through their galaxies. All three forms of feedback radiation, jets, and winds are thought to heat up and expel the cold molecular gas needed to form stars.
At such vast distances, galaxies are much harder to see; they are very small and very weak, from our point of view, here and now. So the researchers had to “stack” the galaxies together to emphasize radio and X-ray emission, which is a sign of an active supermassive black hole that existed billions of years ago.
But it worked: The team found an “excessive” X-ray and radio signal, too strong to be explained by stars alone, in galaxies with little or no star formation. The best explanation for this signal is an active supermassive black hole. Moreover, the signal was not so pronounced in galaxies with ongoing star formation.
This suggests that it is very likely that an active supermassive black hole plays a role in the abrupt death of these mysterious, ghostly galaxies.
Future research, they say, could help shed light on the detailed physics of this enigmatic process.
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