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Identified as a potentially interesting source by ALeRCE (Automatic Learning for the Rapid Classification of Events).
An international group of astronomers, using observations from NASA’s Neil Gehrels Swift Observatory, has, for the first time, discovered signals of a pair of monstrous black holes disturbing a gas cloud at the center of a galaxy.
“This is a very unusual event, known as AT 2021hdr, which we observe increasing in brightness every few months,” said Lorena Hernández-García, an astrophysicist at the Millennium Institute of Astrophysics (MAS) and the TITANS Millennium Nucleus in Chile. “We believe a gas cloud has enveloped the black holes. As they orbit each other, the black holes interact with the cloud, disrupting and consuming its gas. This generates an oscillating pattern in the light emitted by the system.”
A paper on AT 2021hdr, led by Hernández-García, has just been published in Astronomy and Astrophysics.
This twin black hole binary system is located at the center of a galaxy called 2MASX J21240027+3409114, situated a billion light-years away in the northern constellation Cygnus. The pair is separated by about 26 billion kilometers, close enough that light takes only a day to travel between them. Together, they contain 40 million times the mass of the Sun.
Scientists estimate that the black holes complete an orbit every 130 days and will eventually collide and merge in approximately 70,000 years.
AT 2021hdr was first detected in March 2021 by the ZTF (Zwicky Transient Facility) at the Palomar Observatory in California. It was identified as a potentially interesting source by ALeRCE (Automatic Learning for the Rapid Classification of Events). This Chilean broker combines artificial intelligence tools with human expertise to inform the astronomical community of events in the night sky, using vast data sets collected by survey programs like ZTF.
“While the first flare was originally thought to be a supernova, the outbursts in 2022 led us to consider other explanations,” said co-author Alejandra Muñoz-Arancibia, a member of the ALeRCE team and astrophysicist at MAS and the Center for Mathematical Modeling (CMM) at the University of Chile. “Each subsequent event has helped us refine our model of what we believe is happening within the system.”
Alejandra Muñoz-Arancibia, MAS and CMM astrophysicist.
ZTF has detected bursts from AT 2021hdr every 60 to 90 days since the first flare. Hernández-García, who is also a researcher at the Institute of Physics and Astronomy at the University of Valparaíso, and her team have been observing the source with Swift since November 2022. Swift has helped them determine that the system produces oscillations in ultraviolet and X-ray light on the same timescales that ZTF observes in the visible range.
The researchers analyzed various scenarios to explain what the data showed. Initially, they thought the signal might be the byproduct of normal activity in the galactic center. They then considered a tidal disruption event—the destruction of a star that ventured too close to one of the black holes—as the cause. Finally, they opted for another possibility: the tidal disruption of a gas cloud, one larger than the binary black hole system itself.
When the cloud encountered the black holes, their gravity shredded it, forming filaments around the pair and initiating friction that began heating it. The gas also became particularly dense and hot. As the binary system orbits, the complex interaction of forces ejects some gas from the system with each rotation. These interactions produce the fluctuations observed by Swift and ZTF as oscillations.
Hernández-García and her team plan to continue observing AT 2021hdr to better understand the system and refine their models. They are also interested in studying its host galaxy, which is currently merging with a nearby galaxy, an event first reported in their paper.
“With Swift’s 20th anniversary approaching, it’s incredible to see all the new science it continues to help the community achieve,” said S. Bradley Cenko, Swift’s principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, USA. “There’s still so much it can teach us about our constantly changing cosmos.”
Goddard manages the Swift mission in collaboration with Penn State, Los Alamos National Laboratory in New Mexico, and Northrop Grumman Space Systems in Dulles, Virginia. Other partners include the University of Leicester and the Mullard Space Science Laboratory in the UK, Brera Observatory in Italy, and the Italian Space Agency.
Simulation:
ALeRCE Communications.
– Center for Mathematical Modeling, Millennium Institute of Astrophysics, TITANS Millennium Nucleus, and Institute of Physics and Astronomy at the University of Valparaíso.
Center for Mathematical Modeling
The CMM is today the most active scientific research institution in mathematical modeling in Latin America. It is a center of excellence of the National Agency for Research and Development (ANID) of Chile, integrated by eight partner universities and located at the Faculty of Physical and Mathematical Sciences of the University of Chile. It is also the International Research Laboratory (IRL) #2807 of the French National Center for Scientific Research (CNRS).
Its mission is to create mathematics in response to problems in other sciences, industry and public policy. It seeks to develop science with the highest standards, excellence and rigor in areas such as data science, climate and biodiversity, education, resource management, mining and digital health.
Posted on Nov 13, 2024 in News
