The Milky Way is not very active in galaxies. Each year, it produces about three or four new star suns in its entire spiral body, and stars of all ages can be found splattered everywhere.
But there are some even quieter galaxies: elliptical galaxies, for which most star formation ceased long ago. In these galaxies, no or very few stars less than a certain age can be found, suggesting that at some point most star formation ceased abruptly, allowing the galaxy to speak slowly over the eons. , star by star.
Exactly how star formation fades in these smooth, almost unbroken galaxies is a mystery, but astronomers believe it has something to do with the supermassive black holes at the center of each galaxy. Now, an international team of astronomers led by Kei Ito of the Postgraduate University of Advanced Studies, SOKENDAI in Japan has looked back at the initial Universe to find out if this is the case.
Using some of the most powerful telescopes in the world, they have collected data on multiple wavelengths of light to identify galaxies whose light has traveled between 9.5 and 12.5 billion years across space-time gulf: galaxies as ancient as the elliptical galaxies closest to us in space. and time, for whom star formation is about to be extinguished.
The first step was to use optical and infrared data to identify galaxies for which star formation is in progress, and those in which star formation has ceased.
The next step was to use X-ray and radio data to identify the activity of the supermassive black hole. This is the mechanism by which astronomers believe that star formation can be extinguished. When a supermassive black hole is active, it devours large amounts of matter from the surrounding space. This process is messy and violent, producing what is collectively known as “feedback”.
We all know that nothing can emerge beyond the event horizon of a black hole, but the space around it is a different matter. The material revolves around the black hole, like water surrounding a drain; gravity and friction generate intense radiation that burns throughout the universe.
Another form of feedback takes the form of jets coming out of the polar regions of the black hole. The material outside the event horizon is thought to accelerate along the outer magnetic field of the black hole, to be thrown from the poles as powerful focused plasma rays traveling at a significant percentage of the speed of the black hole. light.
Finally, active supermassive black holes generate strong winds that sweep their galaxies. The three forms of feedback (radiation, jets, and winds) are believed to heat and repel the cold molecular gas required for the formation of baby stars.
At such great distances, galaxies are much harder to see; they are very small and very weak, from our point of view in the here and now. So the researchers had to “stack” the galaxies together to emphasize the X-ray light and X-rays that are the telltale signs of an active supermassive black hole all these billions of years ago.
But it worked; the team found an “excess” X-ray signal and radius too strong to be explained by single stars in galaxies with little or no star formation. The best explanation for this signal is an active supermassive black hole. In addition, the signal was less pronounced in galaxies with ongoing star formation.
This suggests, the researchers concluded, that it is highly plausible that an active supermassive black hole will play a role in the sudden death of these mysterious and ghostly galaxies.
Future research, they said, may help shed light on the detailed physics of this mysterious process.
The research was published in The Astrophysical Journal.
Cover Image Credit: NASA, ESA and The Hubble Heritage Team / STScI / AURA; J. Blakeslee / Washington State University.