'Like watching a cosmic volcano erupt': Scientists see monster black hole 'reborn' after 100 million years

Scientists have observed a supermassive black hole waking up from a nearly 100 million-year nap.

The black hole lies at the center of a gigantic galaxy that's emitting extremely strong radio waves. A new analysis of these radio emissions reveals the black hole once spewed gargantuan jets of plasma hundreds of thousands of light-years into space, before suddenly shutting off sometime in the distant past. Those jets are now active once again, and they are interacting in complex and chaotic ways with the superheated gas around them, according to the new study.

"It's like watching a cosmic volcano erupt again after ages of calm — except this one is big enough to carve out structures stretching nearly a million light-years across space," study co-author Shobha Kumari, an astronomer at Midnapore City College in India, said in a statement.

Galactic engine trouble

Only 10% to 20% of supermassive black holes have jets that emit radio signals. In these galaxies, a spinning disk of dust and plasma swirls around the black hole, regularly feeding it large amounts of matter. This infalling matter creates a tangled magnetic field that can fling some matter away from the black hole in giant jets. Changes in the disk can cause these radio jets to turn off and on in rare cases.

In the new study, published Jan. 15 in the journal Monthly Notices of the Royal Astronomical Society, the researchers used the Low-Frequency Array, a radio telescope network located primarily in the Netherlands, to find more than 20 galaxy clusters that housed radio galaxies with irregularly shaped jets. They focused on one such galaxy, called J1007+3540, with a particularly unusual footprint.

The giant galaxy has large, diffuse lobes of plasma that indicate past jet activity dating back some 240 million years. But within those lobes are smaller, brighter plasma jets that are just 140 million years old, the team found. That suggested that the active galactic nucleus (AGN) — the central region that houses a galaxy's supermassive black hole — had kicked back on after a period of silence.

"This dramatic layering of young jets inside older, exhausted lobes is the signature of an episodic AGN — a galaxy whose central engine keeps turning on and off over cosmic timescales," Kumari said.

The space between the galaxies in the cluster that includes J1007+3540 is filled with superheated gas known as the intracluster medium. That gas interacts with the radio jets, bending and shaping them as they extend from the AGN. One of the two older lobes is squished sideways and back toward its source by the surrounding gas. The other lobe has a long, kinked tail that suggests the intracluster medium is interacting with the jets in a different way.

"J1007+3540 is one of the clearest and most spectacular examples of episodic AGN with jet-cluster interaction, where the surrounding hot gas bends, compresses, and distorts the jets," study co-author Surajit Pal, a physicist at the Manipal Centre for Natural Sciences in India, said in the statement.

Observing J1007+3540 will help researchers determine how often AGNs turn on and off and how old jets interact with their surroundings. In future work, the team plans to collect high-resolution observations of the galaxy to map how the jets propagate through the intracluster medium, according to the statement.