Doomed to Collide: Astronomers Announce Discovery of Supermassive Binary Black Holes

Two supermassive black holes revolve around each other in a binary system. They are 10 times closer to each other than black holes in the only other known supermassive binary black hole system. Credit: Caltech/R. Injured (IPAC)

A team of researchers from Purdue University and other institutions have discovered a supermassive[{” attribute=””>black hole binary system, one of only two known such systems. The two black holes, which orbit each other, likely weigh the equivalent of 100 million suns each. One of the black holes powers a massive jet that moves outward at nearly the speed of light. The system is so far away that the visible light seen from Earth today was emitted 8.8 billion years ago.

The two are only between 200 AU and 2,000 AU apart, at least 10 times closer than the only other known supermassive binary black hole system. One AU is the distance from the Earth to the sun, which is about 150 million kilometers (93 million miles) or 8.3 light minutes.

The close separation is significant because such systems are expected to merge eventually. That event will release a massive amount of energy in the form of gravitational waves, causing ripples in space in every direction (and oscillations in matter) as the waves pass through.

Finding systems like this is also important for understanding the processes by which galaxies formed and how they ended up with massive black holes at their centers.

Brief summary of methods

Researchers discovered the system by chance when they noticed a repeating sinusoidal pattern in its radio brightness emission variations over time, based on data taken after 2008. A subsequent search for historical data revealed that the system also varied in the same way in the late 1970s to early 1980s. This type of variation is exactly what researchers would expect if the projected emission from a black hole were affected by the Doppler effect due to its orbital motion as it oscillates around the other black hole. Matthew Lister of Purdue University’s College of Science and his team imaged the system from 2002 to 2012, but the team’s radio telescope lacks the resolution to resolve individual black holes at such a great distance. Its imaging data supports the binary black hole scenario and also provides the orientation angle of the projected flow, which is a critical part of the paper’s model for Doppler-induced variations.

Two supermassive black holes orbiting around

Two supermassive black holes are seen orbiting each other in this artist’s loopable animation. The most massive black hole, which is hundreds of millions of times the mass of our sun, shoots out a jet whose apparent brightness changes as the pair spin around. Astronomers have found evidence for this scenario in a quasar called PKS 2131-021 after analyzing 45 years of radio observations which show the system periodically darkening and brightening. The observed cyclic pattern is thought to be caused by the orbital motion of the jet. Credit: Caltech/R. Injured (IPAC)

Professor Purdue’s Expertise

Matthew Lister, Professor of Physics and Astronomy, Purdue University College of Science, specializes his research in the following areas: active galactic nuclei, astrophysical jets and shocks, quasars and BL Lacertae objects, narrow-line Seyfert I galaxies, very long base.

To learn more about this study:

Reference: “The Unforeseen Phenomenology of Blazar PKS 2131–021: A Unique Supermassive Black Hole Binary Candidate” by S. O’Neill, S. Kiehlmann, ACS Readhead, MF Aller, RD Blandford, I. Liodakis, ML Lister, P Mróz, CP O’Dea, TJ Pearson, V. Ravi, M. Vallisneri, KA Cleary, MJ Graham, KJB Grainge, MW Hodges, T. Hovatta, A. Lähteenmäki, JW Lamb, TJW Lazio, W. Max-Moerbeck, V. Pavlidou, TA Prince, RA Reeves, M. Tornikoski, P. Vergara de la Parra and JA Zensus, February 23, 2022, Letters from the Astrophysical Journal.
DOI: 10.3847/2041-8213/ac504b

Funding: Support for the MOJAVE program includes Nasa– Fermi grants 80NSSC19K1579, NNX15AU76G and NNX12A087G.

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