Astronomers see the last cry of a star in a black hole at the other end of the universe

Astronomers see the last cry of a star in a black hole at the other end of the universe

The light that traveled over 8.5 billion years to reach us was the last gasp of a dying star as a black hole swallowed it.

Two separate teams of scientists have determined that a mysterious glow that appeared in the sky in February 2022, named AT2022cmc, was the astrophysical jet that burst from the massive black hole as the jagged star disappeared beyond its event horizon.

It’s incredibly rare for us to catch one of these in the act, and AT2022cmc is now the farthest we’ve ever seen.

Both articles were published in Nature and natural astronomy.

“The last time scientists discovered one of these jets was more than a decade ago,” says astronomer Michael Coughlin of the University of Minnesota Twin Cities in the United States.

“From the data we have, we can estimate that relativistic jets are launched in only 1% of these destructive events, making AT2022cmc an extremely rare event. In fact, the bright flash from the event is among the brightest ever observed.”

There’s a lot going on in our wild universe, and many encounters and events – supernovae, fast radio bursts, stellar collisions, interactions in compact binaries, and black hole feeding frenzies – are unpredictable, spitting out bursts of temporary lights that blaze across the vastness of space, then fade away.

Only by closely surveying large swaths of the sky can we catch the light of these colossal but transient colossal events.

In February, the Zwicky Transient Facility caught such a blowout. Immediately, 20 other telescopes around the world and in space sprang into action, capturing a wealth of data about the sudden fire over the days and weeks that followed.

From this wealth of information, a team of researchers – co-led by Coughlin and University of Maryland astronomer Igor Andreoni – determined that the event was the result of a tidal disturbance event. The attacker? A rapidly rotating supermassive black hole up to about 500 million times the mass of the Sun, swallowing up stellar matter at a furious rate of half a Sun a year.

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Tidal disturbance events are extreme; they occur when a star moves too close to a black hole. Tidal forces in the gravitational field of this black hole stretch the star, pulling it so hard that it tears apart. The stellar debris then falls onto the black hole.

This process produces a flare of light that fades over time, but we can detect it from Earth if it is bright enough.

That’s not what produced the light astronomers saw from AT2022cmc.

“Things looked pretty normal for the first three days. Then we looked at it with an X-ray telescope, and what we found was that the source was too bright,” says astronomer Dheeraj Pasham of the MIT, who edited the second article.

“That particular event was 100 times more powerful than the most powerful afterglow from the gamma-ray burst. It was something extraordinary.”

Analysis revealed that the cause of the light was an astrophysical jet. When a black hole feeds, sometimes all the material swirling around it doesn’t end up beyond the event horizon.

Magnetic field lines just around the outside of the event horizon act as particle accelerators; some of the matter near the black hole is funneled along these lines, where it is launched from the poles of the black hole at speeds near the speed of light.

In the case of AT2022cmc, one of these jets is pointed straight at us and traveling at 99.99% of the speed of light. When matter moves toward us at near light speed, it appears brighter than it is because the motion produces a change in the frequency of the wavelength of light. This effect is known as relativistic radiation or Doppler amplification because this change is known as the Doppler effect.

AT2022cmc is only the fourth Doppler-boosted tidal disturbance event ever detected.

Scientists expect we can learn a lot from this dying light over half a universe. For example, it is unknown why some tidal disturbance events have jets and others do not. The rapidly rotating black hole can play a key role in the formation of jets.

It is also not known how supermassive black holes form and grow. High power rates, such as those exhibited by the AT2022cmc black hole, could help solve the mystery.

The event was also the first jet tidal disturbance event detected using an optical survey. The amounts of data collected will help astronomers identify more in the future.

“Astronomy is changing rapidly,” says Andreoni.

“More optical and infrared sky-wide surveys are now active or will soon come online. Scientists can use AT2022cmc as a template to learn what to look for and find more disturbing events from distant black holes.

“This means that more than ever, big data mining is an important tool for advancing our knowledge of the Universe.”

The research has been published in Nature and natural astronomy.

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