Tidal shocks can light up the remnants of a star that has been dispersed by a black hole


Tidal shocks can light up the remnants of a star that has been dispersed by a black hole

In a tidal disruption event, a star moves close enough to a supermassive black hole that the black hole’s gravitational pull bends the star until it is destroyed (Image 1). Interstellar matter from the destroyed star forms an elliptical stream around the black hole (image 2). Tidal shocks form around the black hole as gas hits itself on its way back after orbiting the black hole (image 3). Tidal shocks create bright bursts of polarized light observable at optical and ultraviolet wavelengths. Over time, gas from the destroyed star forms an accretion disk around the black hole (image 4) as it is slowly drawn into the black hole. Image size is not accurate. Credit: Jenny Gurmaninen

A new study has shed light on the bright bursts of radiation that are created when a star is destroyed by a supermassive black hole. The explosions do not necessarily form in the vicinity of the black hole, but are created by tidal shocks that occur when gas from the destroyed star collides with itself as it orbits the black hole.

The universe is a violent place where even a star’s life can be cut short. This happens when a star finds itself in a “bad” neighborhood, specifically near a Giant black hole.

These black holes weigh millions or even billions of times the mass of the sun and are usually found in the centers of quiet galaxies. As the star approaches the black hole, it is subjected to the supermassive black hole’s ever-increasing gravity until it becomes stronger than the forces holding the star together. This results in the star being disrupted or destroyed, an event known as a tidal disruption event (TDE).

After a star is torn apart, its gas is formed accumulator disc around the black hole. Bright bursts from the disk can be observed in nearly every wavelength, especially with telescopes and X-ray-detecting satellites,” says postdoctoral researcher Yannis Liudakis of the University of Turku and the Finnish Center for Astronomy with ESO (FINCA).

Until recently, only a few researchers knew of TDE, as there weren’t many experiments able to detect it. However, in recent years scientists have developed the tools to monitor more TDE. Interestingly, but perhaps not surprisingly, these Notes It led to new mysteries that researchers are currently studying.

Notes from extensive experiences with optical telescopes revealed that a significant number of TDEs do not produce X-rays although visible light bursts can be clearly detected. This finding contradicts our basic understanding of disrupted stellar matter evolution in TDEs,” notes Liodakis.

A study published in the journal Sciences An international team of astronomers led by the Finnish Center for Astronomy with ESO suggests that the polarized light coming from the TDE may be the key to solving this puzzle.

Instead of forming a bright X-ray accretion disk around the black hole, the explosion observed in the optical and UV light The detections in many TDEs can arise from tidal shocks. These shocks form far from the black hole as gas from the destroyed star strikes itself on its way back after orbiting the black hole. The bright X-ray accretion disk would form later in these events.

“The polarization of light can provide unique information about fundamental processes in astrophysical systems. The polarized light we measured from TDE can only be explained by these tidal shocks,” says Liodakis, lead author of the study.

Polarized light has helped researchers understand star destruction

The team received a public alert in late 2020 from the Gaia satellite of a transient nuclear event in a nearby galaxy identified as AT 2020mot. The researchers then observed AT 2020mot in a wide range of wavelengths including optical polarization and spectroscopy observations carried out at the Scandinavian Optical Telescope (NOT), owned by the University of Turku. The observations made at NOT were particularly helpful in making this discovery possible. In addition, observations of polarization were made as part of an observational astronomy course for high school students.


The researchers found that the optical light coming from AT 2020mot was highly polarized and changed over time. Despite many attempts, neither radio nor X-ray telescopes have been able to detect radiation from the event before, during, or even months after the peak of the eruption.

“When we saw how polarized AT2020mot was, we immediately thought of a jet shooting out from a black hole, as we often observe around supermassive black holes which accumulate surrounding gases. However, no plane was found,” says Elena Lindfors, an academic research fellow at the University of Turku and FINCA.

The team of astronomers realized that the data closely matched a scenario where a stream of interstellar gas collides with itself and forms bumps near the center and front of its orbit around the black hole. Then the shocks are amplified and ordered magnetic field in the astral stream which would naturally result in highly polarized light. The optical polarization level was too high to be explained by most models, and the fact that it was changing over time made it even more difficult.

“All the models we looked at could not explain the observations, except for the tidal shock model,” notes Kari Kolyonen, who was an astronomer at FINCA at the time of the observations and now works at the Norwegian University of Science and Technology (NTNU).

The researchers will continue to monitor the polarized light coming from the TDEs and may soon discover more about what happens after a star crashes.

more information:
I. Liodakis et al, Optical polarization from the collision of stellar stream shocks in a tidal disturbance event, Sciences (2023). DOI: 10.1126/science.abj9570

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University of Turku

the quote: Tidal shocks can light up remnant of a star that was cannibalized by a black hole (2023, May 12) Retrieved May 13, 2023 from https://phys.org/news/2023-05-tidal-star-black-hole. programming

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