Astronomers from MIT have discovered 18 hitherto unknown black holes, which actively “explode” and “devour” stars. This discovery is already changing the picture of the Universe, doubling the number of events related to tidal destruction (TDE) observed in the local Universe. The discovery of these black holes will help astronomers more accurately estimate the number of such events in the Universe and get closer to theoretical models.
This destruction of a star, called tidal destruction, occurs when the star gets too close to the black hole and the gravitational influence creates enormous tidal forces on the star. As a result of this impact, the star is stretched in the vertical direction and compressed in the horizontal direction, this process is named «spaghettiification». At the same time, the star material forms a disk around the black hole, part of this material is absorbed by the black hole, while the other part “ejects” in the form of jets, accelerating to speeds close to light.
It was previously thought that black holes were capable of tearing and absorbing stars only in galaxies that had recently gone through a period of active star formation. But this study demonstrates that TDE processes can occur in a much broader range of galaxies, which is important for explaining some of the extreme phenomena observed around black holes.
Erin Kara, associate professor of physics at MIT, notes that for a long time scholars have proposed the most exotic ideas to explain these mysteries, but now the moment has come when it is possible to get all the answers.
The MIT team began searching for new black holes, exploding planets, after discovering the closest TDE event to Earth, which was observed in the galaxy NGC 7392, located at a distance of about 137 million light years from Earth.
Scientists developed an algorithm that allowed detecting burst radiation associated with TDE based on data in the infrared range. Using this algorithm and data from NASA’s NEOWISE satellite, astronomers were able to identify the spectra of more than 1000 galaxies at a distance of 600 million light years from Earth.
Analyzing these data and comparing them with the characteristics of TDEs and other phenomena, such as supernova flares, scientists were able to confirm 18 cases of TDE events, caused by the gravitational effects of black holes, resulting in lost stars.
The team of researchers also discovered that star collapse events occur not only in rare galaxies after the end of star formation, but also in other types of galaxies. As it turns out, such events occur even in those galaxies that are filled with dense clouds of dust.
«If you look at the sky and see a group of galaxies, then TDEs will be characteristic for all of them», — said lead author of the research and graduate student of the Institute of Astrophysics and Space Research of the Massachusetts Institute of Technology Megan Masterson.
It was previously believed that the TDE is limited to galaxies at the stage after the completion of star formation. However, this study refuted this idea and showed that such events occur in different types of galaxies. The question was why TDEs occur only in some galaxies, while they are absent in others. The answer to this question lies in the presence of dense clouds of dust in galaxies. Gas and dust are capable of absorbing optical and X-ray radiation, but infrared radiation penetrates through the substance. Earlier observations of TDE were possible only with the use of X-ray and optical radiation. This research showed that the detection of black holes in collapsing stars also requires the use of infrared radiation.
The addition of 18 new observations of the TDE to previously known events of this type allowed the study to determine that galaxies experience similar events approximately once every 50 000 years, which is consistent with previous theoretical predictions.
«This gives us confidence that we do not need exotic physics to explain what we see», — concluded Kara.