Astronomers from St. Petersburg followed the brightest black holes in the universe and found out why they periodically “blink”, lowering or increasing their brightness. Their findings were presented in the journals MNRAS and Astrophysical Journal.
Quasars are supermassive black holes in the centers of distant galaxies that actively absorb matter and “spit” out a part of it in the form of narrow beams of matter, dispersed to near-light speeds, and the energy fluxes they disclose, whose luminosity is tens and hundreds of millions of times greater than the brightness of the Sun.
If the quasar is turned towards us by a “face”, then it becomes especially bright for observers on Earth, because of what such objects are often called “blazars”. The brightness of the blazars periodically changes dramatically, the reasons for which remained a mystery and subject of controversy among scientists in recent years.
Kirill Sokolovsky from the Astrophysical Center of the Lebedev Physical Institute in Moscow, as well as scientists from NASA, St. Petersburg, the Crimean Observatory and the Moscow State University, approached the solution of this puzzle by observing one of the brightest and most famous blazars, galaxy 3C 279 in the constellation Virgo, and another object, CTA-102, located in the constellation Pegasus.
Both of these supermassive black holes were discovered more than 50 years ago, and scientists have long been attracted to the fact that their brightness is constantly and very much changing in all ranges of electromagnetic waves. Recently, both of them have experienced several outbreaks of activity, observations of which helped Sokolovsky and his colleagues to come closer to understanding their essence.
As astrophysicists explain, today scientists adhere to two main hypotheses explaining the variations in the strength of the luminescence of the blazars. Some of them suggest that these “blinkers” are related to the fact that the quasar emission strands do not stand still, but periodically shift to the sides, which makes them less bright. Other astrophysicists believe that the increase and decrease in luminosity is associated with internal processes within these “spittle” of black holes.
Russian and foreign scientists found evidence in favor of the first group of theories, comparing how the brightness of 3C 279 and CTA-102 varied in optical, gamma and radio bands during periods of calm and high activity. To do this, scientists used the orbiting telescopes “Fermi” and Swift, as well as a number of terrestrial radio observatories.
Lighthouses of the Universe
These observations showed that changes in the brightness of the quasar in these ranges occurred not simultaneously, but with some delay. For example, it became more visible for radio telescopes and infrared observatories a few hours later than similar events occurred in the optical and gamma ranges.
Similar behavior of blazars, as well as changes in the structure of their emissions, as astrophysicists suggest, suggest that their brightness changes not as a result of internal processes within their emissions, but as a result of a change in its structure and position in space.
As suggested by Sokolovsky and his colleagues, the spits of 3C 279 and CTA-102 are similar in shape not to a straight line, but to a spiral or some other twisted structure, changes in the position of which significantly affect how bright the quasar will seem observers on Earth.
On the other hand, astronomers do not exclude the fact that there are other mechanisms explaining the part of the “blinking” of quasars. For example, during observations of 3C 279, they documented possible traces of the existence of shock waves inside its emissions, which can rupture this spiral and throw some of its matter into the surrounding space.
As the authors of the article hope, further observations, which Russian scientists conduct with the support of the Russian Science Foundation, will help to find an unambiguous answer to this question. This, in turn, will help astronomers understand the role black holes play in the formation and evolution of galaxies.