Mysteriously bright flash is a black hole jet pointing directly at Earth, astronomers say

Earlier this year, astronomers were monitoring data from the Zwicky Transient Facility, an all-sky survey based at the Palomar Observatory in California, when they detected an extraordinary flash in a part of the sky where no such light is present. had been observed at night. before. By a rough calculation, the flash seemed to emit more light than 1,000 trillion suns.

The team, led by researchers from NASA, Caltech and elsewhere, published their discovery in an astronomy newsletter, where the signal caught the attention of astronomers around the world, including scientists at MIT . Over the next few days, multiple telescopes focused on the signal to gather more data across multiple wavelengths in the X-ray, ultraviolet, optical, and radio bands, to see what could possibly produce so much light. .

Now astronomers at MIT and their collaborators have determined a likely source for the signal. In a study published today in natural astronomy, scientists report that the signal, named AT 2022cmc, likely originates from a relativistic jet of matter exiting a supermassive black hole at near light speed. They believe the jet is the product of a black hole that suddenly began to devour a nearby star, releasing a huge amount of energy in the process.

Astronomers have observed other “tidal disturbance events,” or TDEs, in which a passing star is torn apart by tidal forces from a black hole. AT 2022cmc is brighter than any TDE discovered to date. The source is also the most distant TDE ever detected, some 8.5 billion light-years away, more than halfway across the universe.

How could such a distant event appear so bright in our skies? The team says the jet from the black hole may be pointing directly at Earth, making the signal brighter than if the jet was pointing in another direction. The effect is “Doppler amplification” and is similar to the amplified sound of a passing siren.

AT 2022cmc is the fourth Doppler-boosted TDE ever detected and the first such event observed since 2011. It is also the first TDE discovered using an optical sky survey.

As more powerful telescopes start up in the coming years, they will reveal more TDEs, which may shed light on how supermassive black holes grow and shape the galaxies around them.

“We know that there is one supermassive black hole per galaxy, and they formed very rapidly during the first million years of the universe,” says co-author Matteo Lucchini, a postdoctoral fellow at the Kavli Institute of Astrophysics and Space Research at MIT. “This tells us that they feed very quickly, although we don’t know how this feeding process works. So sources like a TDE can actually be a very good probe into how this process is going.

Lucchini’s co-authors at MIT include first author and research scientist Dheeraj “DJ” Pasham, postdoctoral fellow Peter Kosec, assistant professor Erin Kara, and principal investigator Ronald Remillard, as well as collaborators from universities and institutions around the world. whole world.

Feeding frenzy

After the initial discovery of AT 2022cmc, Pasham and Lucchini focused on the signal using the Neutron Star Interior Composition Explorer (NICER), an X-ray telescope that operates aboard the International Space Station.

“Things seemed pretty normal the first three days,” Pasham recalled. “Then we looked at it with an X-ray telescope, and what we found was that the source was too bright.”

Typically, these bright flashes in the sky are gamma-ray bursts – extreme jets of X-ray emissions that shoot out from the collapse of massive stars.

“This particular event was 100 times stronger than the strongest afterglow from the gamma-ray burst,” says Pasham. “It was something extraordinary.”

The team then collected observations from other X-ray, radio, optical and UV telescopes and tracked signal activity over the following weeks. The most remarkable property they observed was the extreme signal brightness in the X-ray band. They found that X-ray emissions from AT 2022cmc oscillated widely by a factor of 500 within weeks,

They suspected that such extreme X-ray activity must be fueled by an “extreme accretion episode” – an event that generates a huge churning disk, like from a tidal disturbance event, in which a jagged star creates a whirlwind of debris as it falls. in a black hole.

Indeed, the team found that AT 2022cmc’s X-ray brightness was comparable to, though brighter than, three previously detected TDEs. These light events generated jets of matter pointing directly at Earth. The researchers wondered: if the brightness of AT 2022cmc is the result of a similar jet targeting Earth, how fast must the jet be moving to generate such a bright signal? To answer this, Lucchini modeled signal data, assuming the event involved a jet heading directly towards Earth.

“We found that the speed of the jet is 99.99% of the speed of light,” says Lucchini.

To produce such an intense jet, the black hole must be in an extremely active phase – what Pasham describes as a “hyperfeeding frenzy”.

“It’s probably swallowing the star at the rate of half the mass of the sun per year,” Pasham said. “A lot of this tidal disruption happens very early on, and we were able to capture this event early on, within a week of the black hole starting to feed on the star.”

“We expect many more of these TDEs in the future,” adds Lucchini. “So maybe we can say, finally, how exactly black holes launch these extremely powerful jets.”