Technical University of Denmark scientists detect rare black hole phenomenon

A successful and very rare sighting of a luminous jet spewed by a gigantic black hole can help us better understand the nature of these extreme objects.
All known galaxies are supposed to revolve around a gigantic black hole in their centre.

These so-called supermassive black holes, many million times heavier than our sun, occasionally interact violently with stars that come near them.

It’s among the most potent events in the Universe when a star gets close to such a supermassive black hole and is ripped apart while spewing a huge luminous jet of matter into space before being ‘eaten’ by the black hole.

Astronomers call this phenomenon a ‘jetted Tidal Disruption Event’ or jetted TDE.

These are rarely observed events. But now an international team of scientists, led by Igor Andreoni, an astronomer at the University of Maryland and NASA Goddard Space Flight Center, and with the participation of DTU Space scientists, have observed and studied such an event. A description of the event – referred to as “AT2022cmc” – has just been published in the reputable journal Nature.

“The last time scientists discovered one of these jets was over ten years ago. And only four have been observed in total. So it’s a big scientific achievement, and the result of huge international cooperation, that we have now observed a new jetted TDE and been able to describe it in great detail,” says Giorgos Leloudas, a contributing author to the new article in Nature and senior scientist at DTU Space at The Technical University of Denmark.

Another study of AT2022cmc was simultaneously published in the journal Nature Astronomy, with research scientist Dheeraj Pasham at MIT in the US as the lead author and Giorgos Leloudas and his group DTU Space as co-authors.

A rapid black hole spin might be the reason for the rarely observed event
It’s still a mystery why some TDEs launch jets while others do not seem to. According to the scientists involved in the study, the supermassive black hole in the AT2022cmc event and similarly jetted TDEs are likely spinning rapidly to power the highly luminous jets.

“We suggest that a rapid black hole spin may be one necessary ingredient for this jet launching, an idea that brings us closer to understanding the physics of supermassive black holes at the centre of galaxies billions of light years away,” explains Giorgos Leloudas.

Observational data gained by DTU Space scientists helped pinpoint where the rare event occurred and explain it. The event happened in a galaxy 8.5 billion light years away. So the light from the event has travelled 8.5 billion years through space to reach the telescopes observing it.

The theory is that every galaxy, including our Milky Way, revolves around a supermassive black hole in its centre.

When a dying star flies too close to a supermassive black hole, several things happen that create a tidal disruption event: first, the star is violently ripped apart by the black hole’s gravitational tidal forces – a bit similar to how the Moon pulls tides on Earth but with much greater strength. Then, pieces of the star are captured into a swiftly spinning disk orbiting the black hole.

Finally, the black hole consumes what remains of the doomed star in the disk. In rare cases, like the one now observed, some of the matter from the star is spewed into space:

“In some rare cases, the supermassive black hole launches these ‘relativistic jets’, beams of matter travelling close to the speed of light, after destroying a star,” explains Igor Andreoni, the leader of the study and first author of the article in Nature. He and his team discovered the AT2022cmc event in February.

Interaction with nearby stars reveals black holes
The relativistic jets are estimated to be launched in only one per cent of these destructive events, according to Michael Coughlin, assistant professor of astronomy at the University of Minnesota and co-lead on the project.

“The only way we can detect and explore distant gigantic black holes is when they swallow a star. Then they lighten up, and we can observe this light with telescopes. So these discoveries help us to better understand the nature of black holes, not from theories but by observations of real events,” says Giorgos Leloudas.

In another paper published in Nature Astronomy in September this year, Giorgos Leloudas and his team describe the properties of more ordinary TDEs by studying them for the first time in polarized light.

“Looking at the fraction of polarized light from TDEs, we can learn a lot about their nature and geometry,” says Giorgos Leloudas, the lead author of this study.

“Understanding the detailed physics of more ordinary TDEs is necessary if we wish to explain what makes AT2022cmc so unique “.

Scientists from several countries have been involved to produce a treasure trove of new TDE discoveries.

Their work is based on observations and data from some 20 earth and space-based telescopes, such as the ESO Very Large Telescope in Chile, Nordic Optical Telescope in Spain and the Hubble Space Telescope.

“DTU Space scientists are able to participate and contribute to such substantial scientific work due to our strong international cooperation and participation in telescope projects around the world”, states Giorgos Leloudas.