Supermassive black hole ‘snowplow’ could stop star formation in spiral galaxies

Strange, wobbling black hole jets may shape entire galaxies

By Jacek Krivko Edited by Lee Billings

For decades, astronomers have known that supermassive black holes lurk at the hearts of essentially all large galaxies, occasionally feasting on falling material and spitting out powerful jets. But what is less clear is how this activity actually shapes the galaxies around them.

Now researchers have found a key piece of this galactic puzzle by observing a supermassive black hole expelling a wobbling jet in the galaxy VV 340A, about 450 million light-years away from Earth. The jet acts as a cosmic scale snowplow, pushing away gas that would otherwise fuel the formation of new stars. The results were announced at this year’s winter meeting of the American Astronomical Society in Phoenix, Ariz.

“Traditionally, there have been two ways of gas outflow driven by supermassive black holes in galaxies,” says first author Justin Kader, an astrophysicist at the University of California, Irvine. a related paper published in ScienceIn the first, so-called radiation mode, a white-hot, incandescent accretion disk of infalling matter forms around the rapidly feeding supermassive black hole, which heats nearby gas, This hot gas then expands and pushes the cold gas outward, “You can see gas flowing out of the galaxy into these wide-angle binary structures,” Kader explains,

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In the second jet-driven mode, a black hole launches firehoselike jets of particles and radiation from its poles, which kinetically push the surrounding gas away from the galaxy. However, these jets usually increase the stellar inventory of the galaxy as they push and compress clouds of gas which then gravitationally collapse and eject more stars.

However, in VV 340A, Kader and his colleagues found the jet from a supermassive black hole doing something very different from either of these two modes.

VV 340a is a spiral galaxy that is merging with another VV 340b, collectively forming a system called VV 340. In the sky, the pair appears as an astronomical exclamation point, with VV 340b’s disk facing each other as the “dot” of the exclamation point and VV 340a’s edge-on disk forming the “dash.” For Kader and his colleagues, this edge-on orientation was a stroke of luck, allowing them to more easily probe the inner workings of VV340A. They found that what was shooting from the galaxy’s central black hole was not a standard, straight jet. Instead it was a mysterious S-shaped structure, requiring thorough investigation to determine its nature.

Using the infrared eyes of the James Webb Space Telescope, the team can pierce the thick dust clouding the center of VV 340a to discover a massive cloud of extremely hot, ionized plasma spanning approximately 20,000 light-years – much larger than any other black-hole-generated plasma cloud ever observed. Subsequent optical observations at the Keck Observatory in Hawaii confirmed that this ionized plasma was not standing still but was moving outward at extreme speed. Finally, two radio telescopes, Carl G. Radio observations of VV 340A via the Jansky Very Large Array and the Atacama Large Millimeter Array revealed that the plasma was perfectly aligned with the S-shaped jet coming from the black hole.

Kader and his co-authors believe this S shape is the hallmark of precession, the same wobble you see in a rotating top as it slows down or as water spews from the rotating head of a lawn sprinkler. As the black hole rotates, its jet is not just directed in one direction – it sweeps through space in a conical motion, pushing star-forming gas out of the galaxy at a rate of about 20 solar masses per year. The researchers estimate that this is enough to reduce VV 340A’s star-forming lifetime to about 250 million years.

“Twenty solar masses per year is no big deal,” says Andrew Fabian, a British astronomer and former director of the Institute for Astronomy at the University of Cambridge, who was not involved in the study. “But a precessing jet as a driver of gas outflow is something new. It really shows that it can move matter around significantly in a spiral galaxy.” One of the still unanswered questions for Kader and his colleagues is what exactly causes the jet’s wobbly speed.

“These wobbly jets are not common, but they have been observed before, mostly in giant elliptical galaxies,” Kader says, noting that there are currently two main drivers thought for the behavior. One is an accretion disk instability, in which a large mass of gas falling toward the black hole pulls on the disk of material around it, causing it to bend.

The second, arguably more exciting possibility is that VV 340A has not just one black hole at its center, but two. A binary pair of supermassive black holes orbiting each other can gravitationally move the jet around like a garden hose. “To the best of my knowledge, a binary supermassive black hole has never been observed directly before. We do not claim that we have observed HeBut this is one of two possible options,” says Kader.

High-resolution radio observations, combined with studies using future observatories such as NASA’s Nancy Grace Roman Space Telescope, may help discern between these two possibilities. Meanwhile, the team has identified 32 other galaxies similar to VV 340A for further investigation. “What we want to see is the interaction of different gases in the galaxy merger process,” says study co-author Vivian Yu, also at the University of California, Irvine. “Being able to understand this will really allow us to answer one of those big-picture questions – to understand the drivers of the evolution of galaxies.”

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