A mysterious flash from a distant black hole is pointing directly at Earth

30 Nov 2022

Artist’s impression of star being tidally disrupted by a supermassive black hole. Image: M Kornmesser/ESO (CC BY 4.0)

Scientists say the signal is the result of a supermassive black hole devouring a nearby star and releasing vast amounts of energy.

Scientists believe they have discovered the source of an incredibly bright flash that appears to be pointed directly at Earth from halfway across the universe.

A team that included researchers from MIT and the University of Birmingham suggests that the optical and radio signal – named AT 2022cmc – is likely a jet of matter streaking out from a supermassive black hole at close to the speed of light.

They believe the jet is the result of the black hole devouring a nearby star at a rate equivalent to half the mass of our sun per year – releasing incredible amounts of energy in the process.

The findings, published today (30 November) in Nature Astronomy, are expected to shed new light on how supermassive black holes feed and grow.

Known as a tidal disruption event, or TDE, the phenomenon of a supermassive black hole tearing apart a nearby star is not new to scientists. However, AT 2022cmc is brighter and farther away than any TDE discovered to date, at some 8.5bn light years away.

“Our spectrum told us that the source was hot – around 30,000 degrees, which is typical for a TDE,” said Dr Matt Nicholl, associate professor at the University of Birmingham.

“But we also saw some absorption of light by the galaxy where this event occurred. These absorption lines were highly shifted towards redder wavelengths, telling us that this galaxy was much further away than we expected!”

As a possible explanation for why the distant event appears so bright in our sky, the team suggests that the black hole’s jet may be pointing directly towards the Earth – making it appear brighter than it would if the jet pointed in any other direction.

“Things looked pretty normal the first three days,” said first author of the study Dr Dheeraj Pasham of MIT. “Then we looked at it with an X-ray telescope, and what we found was the source was 100 times more powerful than the most powerful gamma-ray burst afterglow.”

This effect is known as Doppler boosting – like the amped-up sound of a passing siren. While AT 2022cmc is the fourth Doppler-boosted TDE ever recorded, it is the first one observed by scientists since 2011.

“Gamma-ray bursts are the usual suspects for events like this,” said Dr Benjamin Gompertz, assistant professor at the University of Birmingham who led the gamma-ray burst comparison analysis.

“However, as bright as they are, there is only so much light a collapsing star can produce. Because AT 2022cmc was so bright and lasted so long, we knew that something truly gargantuan must be powering it – a supermassive black hole.”

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Artist’s impression of star being tidally disrupted by a supermassive black hole. Image: M Kornmesser/ESO (CC BY 4.0)

Vish Gain is a journalist with Silicon Republic