Radio images have captured this “cosmic volcano” being reborn in the heart of the galaxy J1007+3540.
By KR Callaway edited by Lee Billings
After 100 million years of dormancy, the supermassive black hole at the center of the galaxy J1007+3540 shines brightly.
LOFAR/Pan-STARRS/S. Kumari et al.
Inside an incredibly bright cluster of galaxies, a supermassive black hole came back to life. Radio images captured a million-light-year-long stream of star-forming particles and gas emanating from the black hole at the center of galaxy J1007+3540, which is apparently erupting for the first time in about 100 million years.
“Although some ‘rebooted’ radio galaxies are known in the literature, J1007+3540 stands out,” says Shobha Kumari, lead author of the study from Midnapore City College in India. The result recently appeared in the Monthly Notices of the Royal Astronomical Society.
J1007+3540 is an unusually large example of an episodic galaxy, in which a central supermassive black hole only intermittently emits prominent jets of particles and gas, almost as if an astrophysical on-off switch was flipped. The researchers say that the information obtained from the eruption of this “cosmic volcano” could help them better understand the structures, evolution and influence of episodic galaxies on their environment.
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Ejected jets are a constant but not ubiquitous feature of supermassive black holes at the hearts of galaxies, which, when erupting, are also called active galactic nuclei (AGN). Many AGNs are thought to be episodic, decreasing as they deplete surrounding gas reservoirs, only to increase again as more material drifts into their reach. This cycle extends over thousands of years – glacially slow for us but almost instantaneous on a cosmic scale.
This makes episodic activity and on-off transition difficult to detect as they occur. Rather than trying to observe the changes themselves, scientists often analyze structures within galaxies that they think result from episodic explosions from a central black hole. If the black hole is dormant, they look for echoes of its past active phase, such as high-energy light or ionized gas that has moved away from the center of the galaxy. And of course, if a galaxy’s central black hole is in its AGN phase, like the one at J1007+3540, the evidence is clear.
Radio images of J1007+3540, taken using interferometers at the Low Frequency Array in the Netherlands and the Giant Enhanced VHF Radio Telescope in India, capture both phases in a single target. The galaxy sports not only a glowing newborn, but also a surrounding glut of older material destroyed by past episodes of AGN. While other episodic galaxies should have similar structures, those of J1007+3540 are particularly clear.
“This system is physically very large, which makes it easier to study in many ways,” says Niel Brandt, an astrophysicist at Pennsylvania State University. “You can go in and study it in great detail.”
One such detail, a faint, fragmented tail of old material extending into intergalactic space, stirred by subsequent explosions to glow again, shows how the AGN phase of J1007+3540 can impact its cosmic neighborhood, particularly the gas that permeates the galaxy cluster where J1007+3540 resides, known as the intra-cluster medium (ICM). The shape and brightness of the revived tail trace the complex interactions that occurred between the jet ejected from the AGN and the ICM as the jet propagated outward.
“These observations help us understand that the relationship between a galaxy’s jets and the cluster environment is very dynamic,” says Vivian U, an astronomer at the University of California, Irvine. “The jets don’t just make their way through empty space: they are constantly shaped and changed by the gas they encounter.”
There is still much to learn about how interactions with the ICM can change the shape and behavior of a galaxy’s jets, which can trigger (or suppress) the creation of new generations of stars. One way or another, the flickering and beating of AGN at the hearts of galaxies can dictate whether they will glow for eons or fade to a starless black.
“The oddities are exciting,” says Phil Hopkins, a theoretical astrophysicist at the California Institute of Technology. Observing unusual cases like J1007+3540 gives researchers the opportunity to test and improve their models of how this majestic process unfolds.
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