XMM-Newton observes black hole winds, provides insight into galaxy and black hole interactions

by Haygen Warren

Black holes are among the most intriguing and mysterious objects in the universe. They can typically be found at the centers of galaxies, where their incredible gravitational pulls draw in surrounding gasses, planets, stars, and other cosmic material. As this cosmic material spirals into black holes, large, flat accretion disks are created, which — due to the immense heat and forces exerted on the material — causes the disks to heat up and glow from blackbody radiation.

Interestingly, though, black holes only end up consuming a fraction of the gas and material in these accretion disks, with the remaining material being thrown out into space from the disk in multiple directions. In more dramatic cases, this excess material will be ejected into space at speeds so high that the interstellar gas surrounding black holes ends up being cleared away.

The clearing of interstellar gas around black holes means that the black holes will no longer have anything to consume and that no new stars can form in the regions surrounding the black holes — altering the structure of the galaxy. Recently, the European Space Agency’s (ESA) XMM-Newton X-ray observatory observed an average-sized black hole that is clearing the interstellar gas around it using its extreme “black hole wind” — which, before the XMM-Newton observations, had only ever been detected at extreme black holes featuring accretion disks that are at the limit of the amount of matter they can pull in.

“You might expect very fast winds if a fan was turned on to its 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 lead author Miranda Zak of the University of Michigan.

Hubble image of Markarian 817. (Credit: NASA/ESA/Hubble SM4 ERO Team)

As mentioned, the black hole XMM-Newton observed is located at the center of a galaxy named Markarian 817 — an active spiral galaxy located approximately 430 million light-years away from Earth.

“It is very uncommon to observe ultra-fast 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 around a year, while not being in a particularly active state, suggests that black holes may reshape their host galaxies much more than previously thought,” added co-author and astronomer Elias Kammoun of Roma Tre University in Italy.

When an active black hole is located at the center of a galaxy, the center of that galaxy can be called an active galactic center. Given the presence of accretion disks and other extremely hot and bright material surrounding black holes, active galactic centers typically emit high amounts of high-energy light, including X-ray light.

When researchers used NASA’s Neil Gehrels Swift Observatory, or Swift, to observe Markarian 817’s active galactic center, they noticed activity seemingly ceased and the galactic center got unusually “quiet.” Zak recalls the team’s first observations of the galaxy with Swift, saying, “The X-ray signal was so faint that I was convinced I was doing something wrong!”

The Swift observations intrigued the team, so they enlisted the help of ESA’s X-ray XMM-Newton observatory. Data from XMM-Newton showed that the ultra-fast winds of gas and material being ejected from the Markarian 817 black hole were acting as a sort of shield and blocking X-ray light being emitted by the black hole and its accretion disk — explaining the seemingly quiet nature of the black hole. Later observations of the galactic center of Markarian 817 using NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, X-ray telescope showed a result similar to that of XMM-Newton’s.

Additional analysis of the XMM-Newton data showed that the accretion disk of the Markarian 817 black hole created gusty storms that spread over the entire area of the accretion disk — an extreme contrast to the normal singular puffs of gas and material ejected by accretion disks. The winds around the Markarian 817 black hole persisted for hundreds of days and was comprised of three distinct components, with each component moving at a percentage of the speed of light. In other words, the winds being ejected by this black hole were moving extraordinarily fast.

The XMM-Newton Markarian 817 results are helping scientists understand how black holes and the galaxies that surround them interact and influence one another. A lack of interstellar gas surrounding black holes due to extreme cosmic winds is not an uncommon phenomenon — there are several galaxies, including our own Milky Way — that appear to have large, empty regions at their galactic centers where very few to no new stars form. The extreme black hole winds could explain this empty region, but this theory only works if the winds surrounding the black holes are fast enough, sustained for a long enough time, and are generated by black holes with normal levels of activity.

“Many outstanding problems in the study of black holes are a matter of achieving detections through long observations that stretch over many hours to catch important events. This highlights the prime 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,” says XMM-Newton project scientist Norbert Schartel.

Additional observations of galactic centers using X-ray telescopes like XMM-Newton and IXPE will tell scientists more about these empty regions and how black holes and their surrounding galaxies interact.

Zak et al.’s results were published in the Astrophysical Journal Letters.

(Lead image: Artist’s impression of Markarian 817’s black hole. Credit: ESA)

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