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In the depths of space 3.5 billion light-years away, two supermassive black holes are locked in one of the most extreme orbital dances in the Universe. His spiral of unbridled and somewhat erratic death has been documented for decades.
With new observations, astronomers have characterized the way they rotate around each other at the center of a galaxy called OJ 287. In turn, that characterization has helped refine our understanding of whether black holes are ‘hairy’, a conundrum. which has puzzled cosmologists for decades.
OJ 287 is not an ordinary galaxy. It is a blazar, with a highly variable active galactic core and a relativistic jet that radiates to Earth. For more than a century, it has been documented spitting dazzling flashes of radiation at semi-regular intervals.
In essence, the OJ 287 is even more intense than most galactic cores. It does not have one, but two supermassive black holes, and they are chonkers.
The smaller of the two would feed a highly respectable galactic nucleus in its own right, reaching 150 million times the mass of the Sun. The supermassive black hole in our Milky Way galaxy is 4 million solar masses.
The larger of the two is one of the most massive black holes we have ever seen. Tilt the cosmic scales to 18 billion solar masses.
(NASA / JPL-Caltech / R. Hurt / IPAC)
This larger black hole is surrounded by a huge gas and dust accretion disk that spins around it like water surrounding a drain and constantly falling on the object. While this creates radiation, it is not responsible alone for giant eruptions.
You see, the two black holes are in a 12-year orbit, but the smaller of the two is not oriented with the plane of the accretion disk. It is in a highly inclined, highly elliptical precessing orbit. This means that twice each orbit (12 years) the smallest black hole passes through the accretion disk, causing a gigantic flare.
Because their orbit is so irregular, the timing of these eruptions is somewhat different in each orbit: the two eruptions can occur a decade apart or a year.
However, because observational data has been collected since the late 19th century, astronomers have been able to model this orbit and have accurately predicted the two most recent eruptions. One of them occurred in December 2015, and was predicted in three weeks.
But then, in February 2016, something surprising happened. A global scientific collaboration announced that they had detected gravitational waves from a collision between two black holes. This confirmed a prediction made by Einstein’s theory of general relativity a century earlier that the movements of massive objects lose energy in the form of waves that ripple in the Universe.
For most objects, these waves are negligible. But orbiting supermassive black holes should produce waves that are so strong that we can detect the influence of those waves on their orbits and the timing of the eruptions.
Observing and studying gravitational waves allowed scientists to characterize their magnitude and impact; In 2018, this look was added to the model for OJ 287.
The second flare, nicknamed the Eddington flare, after the English astronomer Sir Arthur Eddington, occurred on July 31, 2019. And it was forecasted for the day.
The calculations also included factors that could help assess whether black holes could be described as ‘furry’. First suggested in the 1960s, the “no hair theorem” assumes that black holes can only be characterized by mass, electrical charge, and spin. This would make them perfectly symmetrical, with no other property or ‘hair’ protruding from their surface.
Black holes are quite difficult to explore, so whether or not they have other properties has been an open question. But one way to evaluate hair is to model black holes with and without it, and see which model fits the observation data.
In the case of DO 287, the hairless model further refined the prediction time to just four hours. This suggests that, if hair is present, it is beyond our detection capabilities for now.
“Observational evidence of flare arrival within 4 hours of the actual prediction supports the prominent role of including GW emission effects with 2PN precision while tracking the orbit of the secondary BH. More importantly, our Spitzer observations they limit the famous hair theorem. ” The researchers wrote in their article.
“These observations are setting the stage for observation campaigns that employ the unprecedented high-resolution imaging capabilities of the Event Horizon Telescope, in combination with the Global Millimeter VLBI Array and the space mission VLBI RadioAstron, to spatially resolve the BBH system in the DO 287. “
The research has been published in Astrophysical journal letters.
