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Black holes are thought to devour so much surrounding material that they end the life of their host galaxy. In that process they create a highly energetic object called a quasar that was previously thought to stop the birth of stars. Now researchers have discovered a galaxy that is surviving the ravenous forces of a quasar by continuing to give birth to new stars – about 100 stars the size of the Sun per year.
The discovery made by the Stratospheric Observatory for Infrared Astronomy (SOFIA) may explain how massive galaxies were born even though the Universe is dominated by galaxies that no longer form stars. The results are published in the Astrophysical Journal.
“This shows us that the growth of active black holes doesn’t stop the birth of stars instantly, which goes against all current scientific predictions,” said Allison Kirkpatrick, assistant professor at the University of Kansas at Lawrence Kansas and co-author of the study. . “It’s making us rethink our theories of how galaxies evolve.”
The new instrument, an infrared camera called High-resolution Airborne Wideband Camera-Plus (HAWC +), was installed on the Stratospheric Observatory for infrared astronomy, SOFIA. © NASA
SOFIA, a joint project of NASA and the German Aerospace Center, DLR, has studied an extremely distant galaxy, located more than 5.25 billion light-years away called CQ4479. At the center is a special type of quasar that was recently discovered by Kirkpatrick called a “cold quasar”. In this type of quasar, the active black hole is still feasting on material from its host galaxy, but the quasar’s intense energy hasn’t devastated all the cold gas, so stars can continue to form and the galaxy survives. This is the first time that researchers have examined a cold quasar in detail, directly measuring the growth of the black hole, the birth rate of the stars, and how much cold gas remains to power the galaxy.
“We were surprised to see another whimsical galaxy that challenges current theories,” said Kevin Cooke, a postdoctoral researcher at the University of Kansas in Lawrence, Kansas, and lead author of this study. “If this tandem growth continues, both the black hole and the stars surrounding it would triple in size before the galaxy reaches the end of its life.”
As one of the brightest and most distant objects in the universe, quasars, or “near-stellar radio sources”, are notoriously difficult to observe because they often obscure everything around them. They form when a particularly active black hole consumes huge amounts of material from the surrounding galaxy, creating strong gravitational forces. As more and more material turns faster and faster towards the center of the black hole, the material warms up and shines brightly. A quasar produces so much energy that it often blurs everything around it, blinding attempts to observe the galaxy that hosts it. Current theories predict that this energy heats up or expels the cold gas needed to create stars, stopping their birth and causing a lethal blow to the growth of a galaxy. But SOFIA reveals there is a relatively short period in which the galaxy’s star birth can continue as the black hole party continues to fuel the quasar’s powerful forces.
Rather than directly observing newborn stars, SOFIA used its 9-foot telescope to detect infrared light radiated by the heated dust from the star-forming process. Using data collected from SOFIA’s high-resolution Airborne Wideband Camera-Plus or HAWC + instrument, the scientists were able to estimate the amount of star formation over the past 100 million years.
“SOFIA allows us to see in this short time frame where the two processes can coexist,” said Cooke. “It is the only telescope capable of studying the birth of stars in this galaxy without being overwhelmed by the intense brightness of the quasar.”
The short window of joint growth of the black hole and the star represents an early stage in the death of a galaxy, in which the galaxy has not yet succumbed to the devastating effects of the quasar. Continued research with SOFIA is needed to understand whether many other galaxies go through a similar phase with conjoined black hole and star growth before reaching the end of life. Future observations with the James Webb Space Telescope, which is expected to launch in 2021, would reveal how quasars affect the overall shape of their host galaxies.
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