ITE: Where do stars go when they are “swallowed” by black holes? What happens after they are “killed”?

By | May 18, 2023

The Universe is a violent place, where even the life of a star can be cut short.

Where do the stars go when they die? An international group of astronomers, in which scientists from the Institute of Astrophysics of Technology and Research Foundation and of University of Crete.

In the research telescope, the researchers placed their sudden star deaths. As is well known, the Universe is a violent place, where even the life of a star can be cut short. This, according to scientists, happens when you are in a “bad” neighborhood, specifically the neighborhood of a massive black hole. These black holes They have millions, to billions, of times their mass. Sun and are found in the centers of galaxies. As the star approaches the black hole, it begins to experience its increasing gravity, until that gravity becomes stronger than the forces holding the star together. Then the star will be destroyed and its gas will be swallowed, in part, by the black hole.

These sudden deaths of stars are called Tidal disturbance events (Tidal Disruption Events – TDE). After the star dies, its gas will form a increment disc on his way to the black hole. This leads to a flash usually seen on the optical and ultraviolet spectrumas well as about X-raysbut sometimes even in radio part of the spectrum and in c-rays. Until recently there were only a few TDE acquaintance. Not because they are rare, but because there have not been many experiments capable of detecting them. In recent years that has changed, giving scientists the tools they need to begin to understand how matter behaves at very close distances from a black hole.

But this has led to more questions than answers. Observations from experiments with optical telescopes revealed that a large number of these TDE does not produce x-rays. this comes to contrast with what scientists have hitherto believed about the TDE. The dominant model calls for the rapid formation of an accretion disk, particularly bright in X-rays as soon as the star is destroyed, according to the ERT.

The polarization of light may be the key to solving this mystery. An international team of astronomers, including members of the Institute of Astrophysics (IA) of Technology and Research Foundation (ITE) and University of Cretepublished a study in the journal Science who maintains that for the TDE without X-rays, the formation of the accretion disk is not rapid. Instead, tidal shock waves are formed as gas from the star flows around the black hole. These shock waves are bright in optical and ultraviolet light and form what our telescopes observe as the TDE. The incremental disk is created later.

“The polarization of light can provide unique information about the processes in these astrophysical systems”he says yannis liodakislead author of the study, an astronomer at the Finnish Center for Astronomy with ESO (FINCA) and a graduate of University of Crete. “The polarized light that we measured from TDE could only be explained if we were looking at these tidal shock waves.”

The team received the news in late 2020 from Gaia Satellite for a new one TDE in a nearby galaxy called AT2020mot. So he AT2020mot was observed in a wide range of wavelengths, from radio to X-rays with many different telescopes.

in a tidal disturbance event (TDE), a star will be very close to a supermassive black hole whose gravity will deform it (1) until it is destroyed. The star’s gas follows an elliptical path on its way to the black hole (2). As the gas flows, it collides with itself and forms shock waves near the periphery and at the epicenter of its orbit (3). Shock waves are bright in the optical and ultraviolet part of the spectrum and polarize light. As the phenomenon progresses, the orbit of the gas becomes increasingly circular (4), eventually forming an accretion disk through which stellar gas may eventually be consumed by the black hole.

Particularly important were the observations on polarization in the optical spectrum made in skinakas observatory using the unique polarimeter robopol, that made this discovery possible. “The Skinaka observatory’s RoboPol polarimeter has really been the cornerstone of our studies in trying to understand supermassive black holes.”stated Nikos MandarakasPhD student in AI and University of Crete who conducted the observations and data analysis with the RoboPol.

The scientists discovered that the optical light coming from the AT2020mot, it was highly polarized and its polarization changed over time. Despite many attempts, none of the radio or X-ray telescopes have been able to detect the TDE before, during or even months after its peak. Combining all this information and after comparing the observations with theoretical models, the team of astronomers realized that the data was more consistent with the scenario in which stellar gas collides with itself while orbiting the black hole and forms shock waves in the center and eccentricity of the trajectory Shock waves amplify and order the magnetic field in stellar gas leading to highly polarized light. The level of optical polarization was very high and the fact that it changed over time made it too difficult for most models to explain.

The research also participated in Dmitry Blinovpostdoctoral researcher at Institute of Astrophysics and Kostas Kouroubatzakis like his PhD University of Crete during the observations, who is now a postdoctoral fellow at Astronomical Institute his Czech Academy of Sciences.

Scientists will continue to observe polarized light from the TDE and they may soon find out more about what happens after a star is ‘killed’.

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