Source: NASA
Like a scene out of a sci-fi movie, astronomers using NASA telescopes have found “Space Jaws.”
Lurking 600 million light-years away, within the inky black depths between stars, there is an invisible monster gulping down any wayward star that plummets toward it. The sneaky black hole betrayed its presence in a newly identified tidal disruption event (TDE) where a hapless star was ripped apart and swallowed in a spectacular burst of radiation. These disruption events are powerful probes of black hole physics, revealing the conditions necessary for launching jets and winds when a black hole is in the midst of consuming a star, and are seen as bright objects by telescopes.
The new TDE, called AT2024tvd, allowed astronomers to pinpoint a wandering supermassive black hole using NASA’s Hubble Space Telescope, with similar supporting observations from NASA’s Chandra X-Ray Observatory and the NRAO Very Large Array telescope that also showed that the black hole is offset from the center of the galaxy.
The paper will be published in an upcoming issue of The Astrophysical Journal Letters.
This six-panel illustration of a tidal disruption event around a supermassive black hole shows the following: 1) A supermassive black hole is adrift inside a galaxy, its presence only detectable by gravitational lensing; 2) A wayward star gets swept up in the black hole’s intense gravitational pull; 3) The star is stretched or “spaghettified” by gravitational tidal effects; 4) The star’s remnants form a disk around the black hole; 5) There is a period of black hole accretion, pouring out radiation across the electromagnetic spectrum, from X-rays to radio wavelengths; and 6) The host galaxy, seen from afar, contains a bright flash of energy that is offset from the galaxy’s nucleus, where an even more massive black hole dwells.
Artwork: NASA, ESA, STScI, Ralf Crawford (STScI)
Surprisingly, this one million-solar-mass black hole doesn’t reside exactly in the center of the host galaxy, where supermassive black holes are typically found, and actively gobble up surrounding material. Out of approximately 100 TDE events recorded by optical sky surveys so far, this is the first time an offset TDE has been identified. The rest are associated with the central black holes of galaxies.
In fact, at the center of the host galaxy there is a different supermassive black hole weighing 100 million times the mass of the Sun. Hubble’s optical precision shows the TDE was only 2,600 light-years from the more massive black hole at the galaxy’s center. That’s just one-tenth the distance between our Sun and the Milky Way’s central supermassive black hole.
This bigger black hole spews out energy as it accretes infalling gas, and it is categorized as an active galactic nucleus. Strangely, the two supermassive black holes co-exist in the same galaxy, but are not gravitationally bound to each other as a binary pair. The smaller black hole may eventually spiral into the galaxy’s center to merge with the bigger black hole. But for now, it is too far separated to be gravitationally bound.
A TDE happens when an infalling star is stretched or “spaghettified” by a black hole’s immense gravitational tidal forces. The shredded stellar remnants are pulled into a circular orbit around the black hole. This generates shocks and outflows with high temperatures that can be seen in ultraviolet and visible light.
“AT2024tvd is the first offset TDE captured by optical sky surveys, and it opens up the entire possibility of uncovering this elusive population of wandering black holes with future sky surveys,” said lead study author Yuhan Yao of the University of California at Berkeley. “Right now, theorists haven’t given much attention to offset TDEs. “I think this discovery will motivate scientists to look for more examples of this type of event.”
This is a Hubble Space Telescope image of distant galaxy that is host to the telltale signature of a roaming supermassive black hole.
Science: NASA, ESA, STScI, Yuhan Yao (UC Berkeley); Image Processing: Joseph DePasquale (STScI)
A Flash in the Night
The star-snacking black hole gave itself away when several ground-based sky survey telescopes observed a flare as bright as a supernova. But unlike a supernova, astronomers know that this came from a black hole snacking on a star because the flare was very hot, and showed broad emission lines of hydrogen, helium, carbon, nitrogen, and silicon. The Zwicky Transient Facility at Caltech’s Palomar Observatory, with its 1.2-meter telescope that surveys the entire northern sky every two days, first observed the event.
“Tidal disruption events hold great promise for illuminating the presence of massive black holes that we would otherwise not be able to detect,” said Ryan Chornock, associate adjunct professor at UC Berkeley and a member of the ZTF team. “Theorists have predicted that a population of massive black holes located away from the centers of galaxies must exist, but now we can use TDEs to find them.”
The flare was seemingly offset from the center of a bright massive galaxy as cataloged by Pan-STARRS (Panoramic Survey Telescope and Rapid Response System), the Sloan Digital Sky Survey, and the DESI Legacy Imaging Survey. To better determine that it was not at the galactic center, Yao’s team used NASA’s Chandra X-ray Observatory to confirm that X-rays from the flare site were also offset.
It took the resolving power of Hubble to settle any uncertainties. Hubble’s sensitivity to ultraviolet light also allows it to pinpoint the location of the TDE, which is much bluer than the rest of the galaxy.
This is a combined Hubble Space Telescope/Chandra X-Ray Observatory image of a distant galaxy that is host to the telltale signature of a roaming supermassive black hole. Both telescopes caught a tidal disruption event (TDE) caused by the black hole eating a star.
Science: NASA, ESA, STScI, Yuhan Yao (UC Berkeley); Image Processing: Joseph DePasquale (STScI)
Origin Unknown
The black hole responsible for the TDE is prowling inside the bulge of the massive galaxy. The black hole only becomes apparent every few tens of thousands of years when it “burps” from capturing a star, and then it goes quiet again until its next meal comes along.
How did the black hole get off-center? Previous theoretical studies have shown that black holes can be ejected out of the centers of galaxies because of three-body interactions, where the lowest-mass member gets kicked out. This may be the case here, given the stealthy black hole’s close proximity to the central black hole. “If the black hole went through a triple interaction with two other black holes in the galaxy’s core, it can still remain bound to the galaxy, orbiting around the central region,“ said Yao.
An alternative explanation is that the black hole is the surviving remnant of a smaller galaxy that merged with the host galaxy more than 1 billion years ago. If that is the case, the black hole might eventually spiral in to merge with the central active black hole sometime in the very far future. So at present, astronomers don’t know if it’s coming or going.
Erica Hammerstein, another UC Berkeley postdoctoral researcher, scrutinized the Hubble images as part of the study, but did not find any evidence of a past galaxy merger. But she explained, “There is already good evidence that galaxy mergers enhance TDE rates, but the presence of a second black hole in AT2024tvd’s host galaxy means that at some point in this galaxy’s past, a merger must have happened.”
Specialized for different kinds of light, observatories like Hubble and Chandra work together to pinpoint and better understand fleeting events like these. Future telescopes that will also be optimized for capturing transient events like this one include the National Science Foundation’s Vera C. Rubin Observatory and NASA’s upcoming Nancy Grace Roman Space Telescope. They will provide more opportunities for follow-up Hubble observations to zero in on a transient’s exact location.
The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
ZTF is a public-private partnership, with equal support from the ZTF Partnership and from the U.S. National Science Foundation.
