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| This image is concept illustrates a pair of monster black holes swirling in a gas cloud, a recurring outburst known as AT 2021hdr, studied by NASA’s Swift Observatory and the Zwicky Transient Facility. |
A groundbreaking discovery using NASA’s Neil Gehrels Swift Observatory has revealed the signal from a pair of supermassive black holes disrupting a gas cloud in the center of a distant galaxy, offering new insights into the violent processes occurring in galactic cores.*
The event, named AT 2021hdr, marks the first time astronomers have observed a pair of black holes interacting with a gas cloud in such a unique way. The phenomenon, which recurs every few months, was first detected in March 2021 by the Caltech-led Zwicky Transient Facility (ZTF) at Palomar Observatory in California.
Dr. Lorena Hernández-García, an astrophysicist at the Millennium Institute of Astrophysics and the University of Valparaíso in Chile, explained, “We think that a gas cloud engulfed the black holes. As they orbit each other, the black holes interact with the cloud, perturbing and consuming its gas. This produces an oscillating pattern in the light from the system.”
The black hole pair resides in the center of the galaxy 2MASX J21240027+3409114, located about 1 billion light-years away in the constellation Cygnus. Together, the black holes contain a staggering 40 million times the mass of the Sun. The pair is separated by approximately 16 billion miles (26 billion kilometers) — a distance so small that light takes only a day to travel between them.
Scientists believe that the black holes complete one orbit every 130 days, and in around 70,000 years, they will collide and merge into a single, even more massive black hole.
The ZTF had initially flagged the event as a potential supernova, but as further outbursts were detected, the team began to reconsider the nature of the source. “Each subsequent event has helped us refine our model of what’s going on in the system,” said co-author Alejandra Muñoz-Arancibia, an astrophysicist at the Millennium Institute and the University of Chile.
Using Swift’s observations, the team determined that the oscillations in light observed by ZTF were mirrored in ultraviolet and X-ray wavelengths, confirming that the phenomenon involved more than just a typical supernova. After considering several possible explanations, Hernández-García and her team concluded that the event is likely caused by a tidal disruption of a gas cloud—an occurrence where the intense gravitational forces of the black holes tear apart the cloud, forming filaments of gas that heat up as they interact with the black holes.
As the black holes orbit, their gravitational forces continue to stir and consume the gas, producing the fluctuating light patterns detected by Swift and ZTF. “We’re continuing to monitor this system to better understand the dynamics at play and refine our models of how these events occur,” said Hernández-García.
The discovery also provides a unique opportunity to study the galaxy itself, which is currently merging with a neighboring galaxy, another intriguing aspect of this system highlighted in the team’s recent paper.
The Swift mission, which marks its 20th anniversary next year, continues to be a key tool in advancing our understanding of the universe. “Swift has revolutionized how we study transient cosmic events,” said S. Bradley Cenko, Swift’s principal investigator at NASA’s Goddard Space Flight Center. “There’s still so much more it has to teach us.”
NASA’s Swift mission is part of a global collaboration, working with partners including Penn State, Los Alamos National Laboratory, Northrop Grumman Space Systems, the University of Leicester, Brera Observatory, and the Italian Space Agency. Together, these missions help solve the mysteries of our ever-changing cosmos.