Astronomers discover two black holes “lunching together” in a merger of galaxies


Half a billion light-years from Earth in the constellation Cancer, two supermassive black holes are feeding together following a giant collision of galaxies. Both are only 750 light-years apart, growing frantically as their host galaxies merge.

An international team of astronomers has been able to discover two of these lunching behemoths at such close range for the first time, thanks to the ALMA observatory and the use of a combination of ground-based and space-based telescopes.

As part of an investigation in which astronomers from the CATA of the Universidad Católica and the Universidad Diego Portales played a leading role, it was possible to observe this pair of nearby and active black holes, which penetrate through the large clouds of dust and gas resulting from the galactic merger known as UGC4211, a barrier that until now had not allowed its identification.

The findings, published this week in The Astrophysical Journal Letters and announced at a press conference organized by the American Astronomical Society, will provide a better understanding of what will happen when the Milky Way collides with the nearby Andromeda galaxy and indicate that binary black holes – and the colliding galaxies that give rise to them – could be surprisingly common phenomena in the Universe.

Ezequiel Treister, an astronomer at the Catholic University and co-author of the study, indicates that the discovery would also have implications for the detection of gravitational waves.

“There could be many pairs of supermassive black holes growing in the centers of galaxies that we have not yet been able to identify. If so, in the near future we will observe frequent gravitational waves generated by mergers of these objects throughout the Universe, thanks to future space observatories such as LISA.”

like a puzzle

According to the astronomer and deputy director of CATA, the new discovery was made possible thanks to the combination of data from the ALMA radio telescope with multi-wavelength observations from other powerful telescopes, such as Chandra, Hubble, ESO’s Very Large Telescope and Kek Observatory, Hawaii.

“Each wavelength shows a different part of the picture, like a giant jigsaw puzzle,” Treister explains.

In this way, while the optical images obtained with terrestrial observatories showed the entire galaxy in collision, the Hubble telescope allowed to observe the nuclear regions in high resolution, while the X-ray observations revealed that there was at least one active galactic nucleus in the system.

“ALMA has shown us the exact location of these two supermassive, gluttonous black holes in full swing,” says Ezequiel Treister.

It was thus possible to penetrate the depths of the active galactic nuclei of the UGC4211 merger, explains Claudio Ricci, UDP-CATA astronomer who participated in the research.

“These are areas of the galaxies that are difficult to access because they are compact and extremely luminous, generated by the accretion of matter around the central black holes”.

The astronomer says that surprisingly while investigating with ALMA, the science team discovered not one, but two black holes frantically gobbling up fusion byproducts.

“And they were both feasting very close to each other: just 750 light-years apart,” adds Ricci.

Future of the Milky Way

Franz Bauer, an astronomer at UC-CATA who also participated in the research, points out that with this new information, astronomers will have a better idea of ​​how galaxies similar to ours became what they are now and how they will continue to evolve. .

“So far, the first stages of mergers between galaxies have mainly been studied, but the new observations correspond to the last stages of a collision, anticipating what will happen when the Milky Way collides with the nearby Andromeda galaxy, in about 4,500 million years. “.

The astronomer adds that previous simulations indicated that most of the binary black holes in nearby galaxies must have been inactive objects, “but we were able to observe a pair of black holes in full growth.”

Michael Koss, senior research scientist at Eureka Scientific and lead author of the study, said: ‘We have identified one of the closest pairs of black holes we know of in a colliding galaxy.

“Since we know that these galaxy mergers are much more common in the distant Universe, we can assume that these binary black holes could also be much more common than previously thought,” concluded the astronomer.

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