Astronomers have seen a quiet supermassive black hole in a distant galaxy erupt jets of ultrahot gas, marking the first time a black hole ever "switched on" within human lifetimes.
Observations also hint at an unseen star that may be teetering on the brink of this black hole, but remarkably resisting being swept into the abyss. Studying this doom-defying star could provide long-sought insights into the elusive interactions between the cosmic behemoths and material in the surrounding gas disks that hold sway over their feeding behavior, researchers say.
This particular supermassive black hole, which weighs the equivalent of 1.4 million suns and lurks at the heart of the galaxy 1ES 1927+654 roughly 270 million light-years from Earth, has kept astronomers hooked for the past several years due to its peculiar behavior. After an extended period of quiescence since a mysterious flare-up in 2018, it began steadily emitting X-rays starting in late 2022, signaling to astronomers that yet another powerful but unexplained event was underway.
Indeed, soon after, radio emissions from the galaxy, which had been basically nonexistent, "all of a sudden went up very fast — so fast it was almost suspicious," Eileen Meyer, an associate professor of physics at the University of Maryland, Baltimore County, who led the radio observations, said on Monday (Jan. 13) during an American Astronomical Society (AAS) press conference.
"This is unprecedented — we've never been looking at a black hole and watched it go from being radio quiet to suddenly very radio loud," she added. "It was very fortunate timing."
Images from a network of radio telescopes across the U.S. revealed never-before-seen jets had "turned on," blasting hot blobs of plasma from both sides of the black hole at about one-third the speed of light. While it's unclear what triggered the newborn jets, Meyer and her colleagues suspect the 2018 flare-up — which itself may have been due to the black hole devouring a nearby star — likely played a key role by contributing necessary jet-forming material.
If that's true, the researchers posit the jets will burn for about 1,000 years on material from the ingested star before shutting off. These findings are outlined in a paper published Monday (Jan. 13) in The Astrophysical Journal Letters.
Untold stories
Astronomers have been puzzling over this black hole's behavior since 2018, when it began spewing such intense X-rays that pockets of ultrahot gas above and below its accretion disk, known as black hole coronas, brightened up to 100 times in as little as eight hours — a telltale sign that the cosmic beast was actively feeding on material from the accretion disk. For reasons that are still unclear, the spiked radiation dramatically vanished soon after, but began to rebound almost immediately, eventually shining 20 times brighter than before.
Such wild radiation swings were unprecedented and had astronomers initially doubting the accuracy of the data. However, "when we saw it was real, it was very exciting," astrophysicist Claudio Ricci, an assistant professor at the Diego Portales University in Chile, said in a statement at the time. "But we also had no idea what we were dealing with; no one we talked to had seen anything like this."
A critical puzzle piece came in 2022, when the brightness of X-ray emissions, which until then had fluctuated randomly, started to rise and fall every 18 minutes. Data from the NICER and XMM-Newton space telescopes showed the frequency kept increasing until it reached every seven minutes, where it has hovered since last year.
Pinning down the reason for this continued stability is crucial, researchers say, as it could determine whether the jets themselves are swaying — in which case, however, there is no obvious explanation for why its oscillations would change over time to end up at such high frequency.
The more likely scenario, one that scientists understand better in terms of the physics involved, is that an orbiting companion, lingering very close to the black hole, is extraordinarily resisting being consumed.
A hidden companion
The location and frequency of the X-ray signals suggest any orbiting companion must be within just a few million miles of the behemoth's event horizon, which is the boundary beyond which nothing, not even light, can escape. A tiny black hole would dive right into the supermassive black hole, and any normal star would quickly be torn apart by the behemoth's overwhelming gravitational pull.
Instead, only a white dwarf, the dense corpse of a sun-like star, fits the bill, according to Megan Masterson, a PhD candidate at the MIT Kavli Institute for Astrophysics and Space Research and co-author of an upcoming paper exploring this scenario. The white dwarf would be difficult to shred thanks to being extremely compact, and could have already existed in the accretion disk before moving closer to the black hole, potentially explaining the increasing frequency of X-ray signals observed by the researchers.
Now hovering at the inner edge of the black hole's accretion disk, this stellar remnant might occasionally shed some of its material, which will effectively "give you a little bit of extra energy to keep you outside of the black hole's event horizon," Masterson said during the AAS press conference.
If a white dwarf is at the root of the black hole's puzzling behavior, the system should be emitting gravitational waves: faint ripples in the fabric of space-time that zip through space at light speed. The frequencies of those waves are in the "sweet spot" for detection by the forthcoming Laser Interferometer Space Antenna, or LISA, a gigantic space-based gravitational wave detector that's scheduled to be put in orbit in 2035.
Rough estimates of how much mass the white dwarf is shedding suggest "it should be able to stick around for quite a while," Masterson said. "But who knows? One of things I've learned with this source is that we never really know what's going to happen next."
