(ORDO NEWS) — Black holes, originally predicted by Einstein’s general theory of relativity, are the most extreme object in the known universe.
These objects form when stars reach the end of their life cycle, shedding their outer layers, and have gravity so powerful that nothing (not even light) can escape their surface.
They are also of interest because they allow astronomers to observe the laws of physics under the most extreme conditions.
Periodically, these gravitational giants will devour stars and other objects in their vicinity, releasing massive amounts of light and radiation.
In October 2018, astronomers witnessed one such event while observing a black hole in a galaxy located 665 million light-years from Earth.
Astronomers have already witnessed similar events, but another team from the Harvard and Smithsonian Astrophysical Center noticed something unprecedented while examining the same black hole three years later.
As they explained in a recent study, the black hole shone very brightly because it was ejecting (or “belching”) the remnants of the star’s matter at half the speed of light.
Their results could provide new insights into how black holes feed and grow over time.
The team was led by Yvette Sendes, a CfA research fellow, who was joined by an international team of researchers from the Commonwealth.
Scientific and Industrial Research Organization (CSIRO), Center for Interdisciplinary Research and Research in Astrophysics (CIERA), Space Telescope Science Institute (STScI), Columbia Astrophysical Laboratory, Computational Astrophysics Center of the Flatiron Institute, University of California at Berkeley, Radboud University (Netherlands) and York University in Toronto.
A paper describing their findings recently appeared in the Astrophysical Journal .
As they stated in their paper, the team observed the outbreak by looking at data on tidal disruption events (TDEs) that had taken place over the past few years.
This happens when stars pass too close to black holes and are torn apart during multiple passes, a process known as “s paghettification” due to the way stars are torn into filaments.
In 2018, the TDE in question (dubbed AT2018hyz) was observed by Ohio State University astronomers as part of the Automated All-Sky Supernova Survey (ASAS-SN).
Shortly thereafter, an international team examined AT2018hyz in the visible and ultraviolet bands using the Automated All-Sky Supernova Survey, the Fred Lawrence Whipple Observatory, and the UV Optical Telescope (UVOT). ) at the Neil Gerels Swift Observatory.
This group was led by Sebastian Gomez, a research fellow at the Space Telescope Science Institute and co-author of the new paper. As he explained, TDE was “undistinguished” at the time.
In June 2021, Sendes and her colleagues studied it again using radio data from the Very Large Array (VLA) in New Mexico. To their surprise, they noticed that the black hole had mysteriously come to life. As Sendes explained in a CfA press release:
“It took us by surprise – no one had ever seen anything like it before.
We have applied for director’s discretionary time. on multiple telescopes, and when you find something so unexpected, you can’t wait for the normal cycle of telescope offerings to watch it.
All applications were accepted immediately.”
The team then made follow-up observations of AT2018hyz using multiple telescopes and at different wavelengths.
This included radio observations made with the VLA, the Atacama Large Millimeter-submmillimeter Array (ALMA) observatory in Chile, MeerKAT in South Africa, and the Australian Telescope Compact Array in Australia.
They were merged with X data from the Chandra Space X-ray Observatory and the Neil Gehrels Swift Observatory (respectively).
According to Edo Berger, professor of astronomy at Harvard University and CfA and co-author of the new study, the TDE radio observations were the brightest:
“We have been studying TDEs with radio telescopes for over a decade, and we sometimes find that they glow in radio waves as they erupt material while the star is first being swallowed up by the black hole.
But in AT2018hyz, there was radio silence for the first three years, and now it suddenly lit up become one of the brightest TDEs ever seen.”
The team concluded that this was due to the fact that the black hole was ejecting residual material from the star at relativistic speed (fractions of the speed of light).
This is the first time astronomers have observed such a phenomenon, and the team is not sure why the outflow was delayed by several years.
TDEs are well known for emitting light when they occur, as spaghetti star material is pulled around the black hole and heated, creating a flare that astronomers can see millions of light-years away.
In some cases, spaghetti-like material will be blasted back into space, which astronomers liken to black holes that are “random eaters”. However, outflow emissions usually develop quickly after TDE occurs, not years later.
In short, Sendes said, it’s as if this black hole suddenly started spewing out a bunch of stellar stuff that it ate years ago.
What’s more, these “burps” were extremely energetic: the ejected material reached speeds of up to 50 percent of the speed of light – about five times faster than astronomers have observed with other TDEs. Berger said:
“This is the first time we have seen such a large delay between feeding and churn.
The next step is to look into whether it actually happens more regularly and we just didn’t study TDE late enough in their evolution.”
These results, along with observations of similar events, will help astronomers better understand the feeding behavior of black holes.
This, in turn, could provide insight into how they grow and evolve over time, and their role in galactic evolution.
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