When two black holes meet, they are drawn to one another by way of their enormous gravity, initiating a powerful orbital dance, spiraling closer together over time, until one subsumes the other and they merge.
One of the most energetic events in the universe, actually seeing a binary black hole system in action has proven elusive until now.
A group of scientists report that they have captured the first image of two black holes circling each other once every 12 years or so, around 5 billion light years away from Earth. The pair are at the center of a quasar called OJ287, an extremely bright galactic core that forms when the black hole at the center of the galaxy devours surrounding gas and dust.
The observations, detailed in a study published Thursday in The Astrophysical Journal, offer a rare insight into the interactions of the universe’s most mysterious beasts.
Match made in heaven
Using a system of radio telescopes, the scientists behind the new study identified the pair of black holes through the jets of particles they emit. We can’t see black holes directly since light itself cannot escape them, but they can be detected by the faint glow of gas surrounding them like a halo.
The bigger black hole of this pair is around 18 billion times more massive than the Sun, emitting a giant, bright jet of particles. The smaller of the two, a mere 150 million times the mass of the Sun, is twisted, appearing as a “wagging tail,” according to the researchers.
That’s because the smaller black hole is spinning around the larger one at a much faster speed, and its jet is twisting in different directions during the wild ride.
The study authors caution that more images of the same or higher resolution are needed to absolutely confirm that the “wagging tail” really is the smaller black hole’s jet. If it does indeed belong to the second, smaller black hole, then the jet should appear in a different place and shape every time it is observed. The authors point to 2032 as the next optimal time to observe the “wagging tail,” due to these behemoths’ orbital period.
Drawing back a veil of light
The quasar in which these two black holes are situated is exceptionally bright, flashing light that is some trillion times brighter than the light of our Sun. Scientists have been observing this particular quasar since the 19th century. Back then, however, astronomers didn’t know why it was so bright—indeed, they didn’t know that black holes existed.
It was only in the late 1980’s that scientists began to speculate that the quasar’s bright flares may be the result of two black holes. While the primary, larger black hole is the source of most of OJ287’s light, the secondary black hole can occasionally cause the quasar to flare. In 2021, NASA’s Transiting Exoplanet Survey Satellite (TESS) detected OJ287 brightening by about two magnitudes for a period of roughly 12 hours. The bright flare was attributed to the jet of a second black hole crossing the accretion disk of its larger partner.
To confirm that theory, the scientists behind the new study captured a high resolution image of the pair, so much so that the two black holes appear separate from one another. It comes just six years after astronomers unveiled the very first image of a black hole ever taken. In doing so, the researchers have helped pull back the curtain on some of the most mysterious objects in the universe—information that could help us better understand how the cosmos formed, and how it evolves over time.