What do quasars emit

Cold quasars and the evolution of galaxies

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December 01, 2020, 10:35 a.m.

SOFIA observes the formation of stars in the galaxy CQ4479 although a quasar is raging in the center. Information from the University of Stuttgart, German SOFIA Institute.

Artist's impression of the galaxy CQ4479, in the center of which a quasar is raging. With SOFIA it was observed that the cold gas (shown in brown) in this galaxy can withstand the enormous radiant energy of this quasar for at least a while, so that stars still form at a rate of 100 solar masses per year (shown in blue).
(Image: NASA, Daniel Rutter)
Quasars - quasi-stellar radio sources - are the most luminous objects in the universe, the high-energy radiation of which is generated by the incidence of matter into the massive black hole in the center of a galaxy. The resulting radiation is so intense that it blows away the free gas, which has not yet become stars and planets, and thus prevents any further formation of stars in this galaxy - according to popular belief. With SOFIA, scientists have now discovered a galaxy in which star formation still continues at a rate of around 100 solar masses per year, although the black hole inside is very active. The results have now been published in the Astrophysical Journal.

"This shows us that active black holes do not immediately stop the birth of stars, which contradicts current scientific assumptions," said Allison Kirkpatrick, junior professor at the University of Kansas and co-author of this study. “We have to rethink the theories of how galaxies evolve.” Kirkpatrick recently discovered galaxy CQ4479 at a distance of 5.25 billion light years and found that at its center there is a special so-called “cold quasar”. CQ4479's active black hole feeds on its home galaxy, but has not yet swallowed up all of the cold gas, so stars continue to be formed. This is the first time the researchers have succeeded in gaining a detailed insight into a “cold quasar” and measuring the growth of the black hole, the birth rate of stars and the amount of remaining cold gas. "We were surprised to see yet another bizarre galaxy that defies popular theories," said Kevin Cooke, postdoctoral fellow at the University of Kansas and lead author of the paper. "If this tandem growth had continued, in the end both the mass of the black hole and the number of surrounding stars would have tripled."

Quasars are the brightest and most distant observable objects in our universe and are therefore very difficult to study. They form when active black holes consume more and more matter from their home galaxy. This creates great gravitational forces, the matter circles faster and faster around the black hole, loses energy through friction or collisions and is ultimately swallowed. The matter is heated so much that it glows brightly. A quasar emits so much energy that its radiance exceeds that of the entire galaxy. According to current theories, the cold gas, which is necessary for the formation of new stars, is blown out of the galaxy by this strong radiation and thus the formation of further stars is stopped. SOFIA has now succeeded in investigating the relatively short period of time in which the star formation phase of the host galaxy defies the destructive forces of the quasar.

For this purpose, SOFIA has detected the infrared radiation of the dust, which is heated by the process of star formation. Kevin Cooke and Allison Kirpatrick's team carried out measurements with the high-resolution Airborne Wideband Camera-Plus (HAWC +) on board SOFIA and estimated the star formation rate over the last 100 million years. “SOFIA enables us to look into the short time window in which the two processes run simultaneously,” says Cooke. "It is the only telescope that is able to observe the formation of stars in this galaxy without being outshone by the intensely shining quasar."

The short period in which star formation is not yet inferior to the devastating influence of the quasar is also the beginning of the end of the star formation phase of a galaxy. Further investigations with SOFIA must show whether other galaxies also go through such a stage with the simultaneous growth of the black hole and an increase in the number of stars before their star formation phase ends. Studies of the effects of quasars on the overall structure of their host galaxies are also planned with NASA's James Webb Space Telescope, which is scheduled to start in 2021.

Original publication:
Dying of the Light: An X-Ray Fading Cold Quasar at z ~ 0.405
Cooke, K. C. et al., 2020 ApJ 903 106

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Source: University of Stuttgart

Author: Raumfahrer.net editors