Billions of light-years away, deep in space, are the brightest objects in the Universe. Scientists call them quasars (from the English quasar, quasi stellar object). These are extremely energetic phenomena that arise when a huge supermassive black hole, In the center of a galaxy, it begins to devour all matter that is close. Before falling into its jaws, however, that matter rotates around it at enormous speeds, producing an enormous amount of energy, which is released through the poles of the black hole in the form of bright beams of light rays, but also infrared, ultraviolet and X-rays.
These black holes are believed to devour so much material that they end up annihilating their host galaxies, preventing them from continuing to form stars. But now, and for the first time, a team of researchers has managed to find a survivor. A galaxy that, for now, has survived the voracity of a quasar and that, despite it, continues making about 100 stars the size of the Sun each year.
The discovery, carried out by the Stratospheric Observatory for Infrared Astronomy (SOFIA), could explain the reason why galaxies like ours have managed to become so massive despite the fact that, billions of years ago, the Universe seemed to be dominated by galaxies that no longer form stars. The results of the investigation have just been published in « The Astrophysical Journal».
According to Allison Kirkpatrick, co-author of the study, “This shows us that the growth of active black holes does not stop star birth instantly, which goes against all current scientific predictions. Our finding is making us rethink all of our theories about how galaxies evolve.
Observing a cold quasar
The SOFIA observatory, consisting of a 2.5-meter infrared reflector telescope mounted on a modified Boeing 747 aircraft, is a joint project of NASA and the German Aerospace Center (DLR). The instrument observed a galaxy called CQ4479 that is 5.250 million light years away away and at the core of which is a special type of quasar, recently discovered by Kirkpatrick and classified as a “cold quasar.”
In this type of quasar, the active black hole also feeds on material from its host galaxy, but the intense energy released has not destroyed all the available gas, so the stars can continue to form and the galaxy therefore continues. live. This is the first time that researchers have gotten a detailed look at a cold quasar and have managed to directly measure the growth of the black hole, the rate of star birth, and the amount of gas left to power the galaxy.
“We were very surprised to see a galaxy that was strange and capable of challenging current theories,” says Kevin Cooke, lead author of the study. If this tandem growth continues, both the black hole and the stars that surround it would triple in size before the galaxy reaches the end of its life.
A crucial moment
Despite being among the brightest objects in the Universe, quasars are paradoxically very difficult to observe, since their brilliance often outshines everything around them and blinds the telescopes trying to capture its details. Current theories predict that all this energy overheats or expels the “cold gas” necessary for new stars to form, thus paralyzing the growth of the galaxy. But SOFIA has revealed that there is a relatively short period in which the birth of new stars can continue, and at the same time that the black hole continues to feed the powerful forces of the quasar.
Instead of trying to directly observe newborn stars, the researchers captured the infrared light radiating from the heated powder by the star formation process. In this way, they were able to find out the number of new stars that the galaxy has formed during the last 100 million years.
“SOFIA allows us to take a look at the short time window in which the two processes can coexist,” Cooke explains. It is the only telescope capable of studying the birth of stars in that galaxy without being overwhelmed by the intense luminosity of the quasar.
The short period of time in which the growth of the black hole and the birth of new stars coexist represents, in reality, a very early phase of the death of a galaxybut at a time when it has not yet succumbed to the devastating effects of the quasar. Now, researchers will continue to use SOFIA to find out whether other galaxies also go through a similar stage before the end of their lives. Future observations with the James Webb space telescope, which is scheduled to launch in 2021, will be able to tell us how quasars are generally affecting their host galaxies.