Astronomers have discovered a black hole with unusual behavior, including a hitherto unknown phenomenon

It is relatively common for Black hole A star swallows when it ventures too close to it. But a team of astronomers discovered with astonishment that one of them was still rejecting remnants of stellar material nearly three years after eating its “meal.” This is the first time this phenomenon has been observed and this discovery could help to better understand tidal rupture events.

Tidal rupture event (or TDE, for tidal disturbance event) is a phenomenon that occurs when a star gets close enough to the event horizon of a black hole to be deformed and then torn apart (known as “sweating”) by last tidal forces. Particularly intense electromagnetic radiation follows: stellar matter stretches around the black hole, heats up and creates a flash of light that astronomers can easily spot, even from millions of light years away.

One such TDE, dubbed AT2018hyz, occurred in October 2018, about 665 million light-years from Earth. But radio data recorded by the Very Large Array (VLA) in New Mexico showed that the offending black hole mysteriously revived in June 2021, nearly three years after the event. ” It totally surprised us: no one had ever seen anything like this before “,” Yvette Sindis’ commentsa research associate at the Harvard and Smithsonian Center for Astrophysics and lead author of the study analyzing the phenomenon.

A scan occurred at all wavelengths

The black hole suddenly began to glow even though it hadn’t absorbed any other body in the meantime – a behavior that immediately piqued the interest of scientists. So Cendes and his collaborators took a closer look at TDE.

The team was exceptionally able to immediately take advantage of the observation time on several telescopes to explore this atypical phenomenon. Thus they were able to collect data at multiple wavelengths, from the VLA, the ALMA observatory in Chile, the MeerKAT in South Africa, the Australian Telescope Compact Array, but also from the Chandra and Swift satellite observatories.

“ We present the late radio/millimeter detections (plus optical/UV and X-ray detections) of the tidal rupture event (TDE) T2018hyz, spanning 970–1300 days after optical detection. ‘, Write researchers in Astrophysical Journal. Optical, ultraviolet, and X-ray observations of the TDE generally follow the fall and accretion of stellar mass, while radio observations can reveal outflows of material outgoing into space. When a star is a spaghetti, some of its material is sometimes thrown back into space – what experts call an “outflow”.

Here, the radiofrequency observations of TDE were shown to be particularly atypical. usually black holes Material is ejected after a star is consumed and the phenomenon is clearly visible in radio waves, explains Ido Berger, a professor of astronomy at Harvard University and co-author of the study. ” But in the case of the AT2018hyz, there was wireless silence for the first three years, then brightened dramatically to become one of the brightest wireless TDEs ever. This is the first time researchers have witnessed such a long delay.

A loud cosmic burp

However, the AT2018hyz event was apparently completely normal when it was first observed in 2018.” We tracked the AT2018hyz in visible light for several months, until it disappeared, and then we forgot about it Says Sebastian Gomez, a postdoctoral researcher at the Space Telescope Science Institute and co-author of the study. Data collected at that time However, it made it possible to estimate the mass of the swallowed star: it had only a tenth of the mass of our Sun. The mass of the black hole is estimated to be 5.2 × 10 .⁶ solar masses.

The outflow usually appears shortly after TDE and not years later as observed in AT2018hyz. ” Our multi-frequency data allow us to directly determine the radius and power of the radio transmitter flux, and we found from our modeling that the outflow started approximately 750 days after optical detection ‘ sums up the team.

” It’s as if this black hole suddenly started ejecting a bunch of material from the star it ate years ago. Not only was this stream of matter incredibly late, but it also turned out to be much faster than usual: the team calculated that matter is moving at 50% of the speed of light — while the outflows from TDE typically move about 10% of the velocity from the light!

The team doesn’t yet know why this flow of material has been delayed by several years, but it conjures up several possible explanations. This sudden, delayed activity may first result from a change in the state of the accretion disc. Another explanation might be that the original magnetic field of a sinking star must not have a magnetic field strong enough to operate a relativistic jet; The required magnetic field could only have been generated later, via an alternate source. Finally, it is possible that the relativistic jet has been present since the beginning of the TDE, but was not able to traverse the gas and debris cloud, which was particularly dense at the beginning of the phenomenon.

The next step would be to determine if this phenomenon occurs more regularly; It may be that astronomers haven’t observed TDEs long enough to notice…

source : Y. Cendes et al. The Astrophysical Journal