March 1, 2024

A black hole emptied your neighborhood

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An artist’s illustration of a supermassive black hole (SMBH). The SMBH in a distant galaxy expelled all the material from its accretion disk, clearing a vast area. Credit: ESA

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An artist’s illustration of a supermassive black hole (SMBH). The SMBH in a distant galaxy expelled all the material from its accretion disk, clearing a vast area. Credit: ESA

We can’t see them directly, but we know they are there. Supermassive black holes (SMBHs) probably inhabit the centers of all large galaxies. Their crushing gravity draws material toward them, where it accumulates in an accretion disk, awaiting its turn to cross the event horizon into oblivion.

But in one galaxy, the SMBH choked on its meal and spat it out, sending material flying at high speed and clearing the entire neighborhood.

We’ve known there’s something at the heart of large galaxies since the early 1960s, when astronomers discovered an unexplained radio source at the center of a giant elliptical galaxy. Astronomers thought it was a star, but its spectrum didn’t make sense. And because it was so far away, about 2.4 billion light years away, that meant it was emitting the energy of hundreds of galaxies. The rate of light emitted by the object varied, and the term quasar (near-stellar object) was created to describe it.

More quasars were discovered in the following years, and eventually astronomers realized that gas falling into a massive, compact object could create what they were seeing. Further studies showed that the gas forms a rotating disk around the object, called an accretion disk. Astronomers have also observed stars moving strangely close to the centers of galaxies, and only a massive object could explain their speeds and movements.

In the 1970s, astronomers thought that one of these massive objects existed at the center of the Milky Way. In 1974, astronomers discovered it and named it Sagitarrius A-star. Eventually, more and more evidence showed that most, if not all, large galaxies have SMBHs at their centers. We now understand the link between the accretion disk, the black hole and active galactic nuclei (AGN), which are black holes that actively consume material and emit a lot of radiation.

So, this is our current panorama of small and medium-sized companies. They are massive and compact objects that hide in the centers of galaxies. They can be hundreds of millions, even billions, of solar masses. SMBHs attract material toward them and the material is collected in an accretion disk. The disk heats up and emits radiation, and tangled magnetic fields cause astrophysical jets to shoot from the poles.


Artist’s impression of a supermassive black hole with a rotating accretion disk and astrophysical jets. Credit: NOIRLab/NSF/AURA/J. da Silva

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Artist’s impression of a supermassive black hole with a rotating accretion disk and astrophysical jets. Credit: NOIRLab/NSF/AURA/J. da Silva

Not all of the accretion disk material goes beyond the event horizon. SMBHs consume only a fraction of the disk material. Once they reach the Eddington Limit, the rest are sent into space, dragging some of the gas from the galactic center with them.

Astronomers detected a distant SMBH in the galaxy Markarian 817 that shattered this image. Beyond the accretion disk of an SMBH, the neutral gas and dust form a torus. In the same region, star-forming interstellar gas clouds reside just beyond the gravitational reach of the SMBH. The distant SMBH sent so much material from the disk into space at high speed that it eliminated all the gas in the region. This stifled star formation in the galactic center.

The discovery is presented in new research in The letters from the astrophysical journal. It’s titled “Fierce Feedback in a Sub-Eddington Obscure State from the Seyfert 1.2 Markarian 817”. The lead author is Miranda Zak, an undergraduate researcher at the University of Michigan.

Astronomers have already found SMBHs that are moving material away from their galactic centers. They call this the “black hole wind” and have detected it around extremely bright accretion disks that have reached the limit of how much material they can accumulate. The wind from the black hole throws excess material into space.

But on Markarian 817 the disk is not very bright. This means it should not be at the Eddington Limit or the mass accumulation limit. It’s just a “snack,” according to a press release announcing the discovery.

“We could expect very fast winds if a fan was turned on at the highest setting. In the galaxy we studied, called Markarian 817, the fan was turned on at a lower power setting, but there were still incredibly energetic winds being generated.” said study co-author Miranda Zak.

In scientific terms, these winds are called ultra-fast flows (UFOs). UFOs have speeds of many million kilometers per hour, and astronomers have discovered that they come from accretion disks that have reached their Eddington Limits. But this is different.

“UFOs are often detected at or above the Eddington boundary; This result signals that black hole accretion has the potential to shape host galaxies even at modest Eddington fractions,” the authors write in their research.

Accreting black holes and resulting UFOs could quench star formation near the galactic center, blowing all the gas away. The strong wind also carries away the SMBH’s fuel and, without new gas to power its accretion disk, it emits much less light.

“It is very unusual to observe ultrafast winds and even less common to detect winds that have enough energy to alter the character of their host galaxy. The fact that Markarian 817 produced these winds for about a year even though it was not in a particularly active period This state suggests that black holes can reshape their host galaxies much more than previously thought,” added co-author Elias Kammoun, an astronomer at Roma Tre University in Italy.

Several telescopes and observatories contributed to this discovery. When material in an accretion disk heats up, it emits X-rays. However, when researchers observed Markarian 817 with NASA’s Swift observatory, the X-rays were nearly undetectable. “The X-ray signal was so weak that I was convinced I was doing something wrong!” exclaimed lead author Miranda Zak.

But Swift isn’t our best X-ray observatory. So astronomers turned to ESA’s XMM-Newton X-ray observatory. These observations showed that Markarian 817’s UFO was blocking X-rays from the corona of SMBH, the hole’s immediate surroundings. Another X-ray observatory, NASA’s NuSTAR telescope, confirmed these observations: the X-rays were there, just obscured.

The Markarian 817 UFO only lasted about a year. But during that time, he reshaped the center of the galaxy. This study shows in clear detail how black holes and their host galaxies shape each other and have powerful effects on each other’s evolution.

The study also sheds light on why some galactic centers, including the Milky Way, do not exhibit much active star formation. The SMBHs at their centers expelled star-forming gas. But this can only happen if the UFO is powerful enough and long-lasting enough.

The accumulation and feedback of SMBH, and how it shapes the galaxy that hosts it, is something astrophysicists are eager to learn more about. In this case, ESA’s XMM-Newton played a critical role in determining what was going on in Markarian 817.

Norbert Schartel is project scientist at XMM-Newton. Although he is not directly part of this research, Schartel spoke about the importance of XMM-Newton in deciphering what is happening near SMBHs.

“Many outstanding problems in the study of black holes are a matter of achieving detections through long observations extending over many hours to capture important events. This highlights the paramount importance of the XMM-Newton mission for the future. No other mission can deliver the combination of its high sensitivity and its ability to make long, uninterrupted observations,” Schartel said.

More information:
Miranda K. Zak et al, Fierce Feedback in a Dark State, Seyfert’s Sub-Eddington 1.2 Markarian 817, The letters from the astrophysical journal (2024). DOI: 10.3847/2041-8213/ad1407

Diary information:
Astrophysical journal letters

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