A new study published in Nature shows that supermassive black holes play a critical role in determining when large galaxies stop producing new stars, a process known as "quenching". Sometimes, however, it can also be observed by looking at the energetic radiation from the active galactic nucleus. This happens by heating and dispelling the gas that would have otherwise turned into stars as it gets condensed and cools down.
Every galaxy is believed to have a supermassive black hole at its centre just like Milky Way's Sagittarius A*.
Jean Brodie, professor of astronomy and astrophysics at UC Santa Cruz and a coauthor of the paper, said in the statement: "This is the first direct observational evidence where we can see the effect of the black hole on the star formation history of the galaxy". However, any visible evidence for the determination of a connection between supermassive black holes and the formation of the star was missing. This interplay between the two affects the generation of each star as the galaxy evolves.
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The theory of AGN interrupting formation of new stars lacked observational evidence, until Ignacio Martin-Navarro, a post doctoral researcher at the University of California, Santa Cruz and his team informed that they have the evidence which confirms it. They determined the age of stars in distant galaxies by measuring different light wavelengths they produced and compared that data with the size of supermassive black holes at the centre, which had been measured previously. "We used black hole mass as a proxy for the energy put into the galaxy by the AGN, because accretion onto more massive black holes leads to more energetic feedback from active galactic nuclei, which would quench star formation faster".
Supermassive Black Holes have always been the area of interest for researchers and cosmologists. So star formation lasted longer in those galaxies with smaller central black holes."Numerous other researchers have been trying to establish a correlation between the luminosity of the AGN and star formation with no success".
"For galaxies with the same mass of stars but different black hole mass in the centre, those galaxies with bigger black holes were quenched earlier and faster than those with smaller black holes", said study co-author Martín-Navarro. The formation of a star takes hundreds of millions of years while the outbursts from the AGN occur over a much shorter timescale.
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This illustration from NASA shows a black hole with a disk and a jet. AGNs are highly variable with their properties varying according to the size of the respective black hole, the rate of acceleration of any new material diving into the hole and many other factors.
The observation particularly reveals that black holes have some role in slowing down star-formation activity but the precise nature of this role still remains unclear. Theorists have been coming up with various ideas related to the quenching activity and there might be numerous ways a black hole radiates out its energy into a certain galaxy.
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