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Dancing gigantic black holes play on cue

Astronomers were able to test the main consequences of Einstein’s theories by examining how a few black holes move around each other.

One of these objects is a true colossus – a hole that weighs 18 billion times the mass of our sun; the other one is not quite as big with “only” 150 million solar masses.

The scientists were able to predict their interactions very precisely.

They did this by including their distortion effects on space-time and assuming that the larger hole had a smooth “surface”


The black hole pairing known as OJ 287 exists approximately 3.5 billion light years from Earth.

Scientists have long recognized a sudden brightening of this system that occurs twice every 12 years. The energy outbreak corresponds to a trillion suns that light up simultaneously in the host galaxy of the holes.

The best explanation for this extraordinary behavior is that the smaller object routinely crashes through a gas and dust disc that accumulates on its larger companion, heating the inspiring material to extremely high temperatures.

But this flare is somewhat irregular. Sometimes the brightening episodes only occur every 12 years after 12 years. at other times up to 10 years apart.

It speaks for the complexity of the path that the small hole around its partner takes – a complexity that the research team has now built into a sophisticated model.

“The orbit of the smaller black holes is running, so the times of impact vary,” said Prof. Mauri Valtonen from the University of Turku, Finland. “We had a model back in 1996 that more or less predicted what would happen, but we’ve become more and more accurate,” he told BBC News.

One of the important parameters of the updated model is the energy that radiates away from the system in the form of gravitational waves. These waves in the structure of space-time – described by Einstein’s general theory of relativity – are generated by the acceleration of bodies; and under the extremely massive circumstances of OJ. 287 they have a significant impact on how the system works.

The major test of the latest model took place on July 31 last year, when the appearance of the latest flaring was determined within 2.5 hours of the expected equations.

Graphics: Spitzer, now retired, was the only telescope to make the observations
Graphics: Spitzer, now retired, was the only telescope to make the observations

The event was captured by the NASA Spitzer Infrared Telescope – a happy observation, as it turned out, since OJ 287 was on the other side of the sun at this time and was therefore not visible to ground-based facilities.

Spitzer’s separation from Earth (160 million km), however, put her in the best position.

“When I first checked the visibility of OJ 287, I was shocked to see that it was visible to Spitzer on the very day the next flare was predicted,” said Dr. Seppo Laine, a scientist from Caltech, United States, who oversaw the Spitzer observation.

“It was very fortunate that we were able to capture the peak of this torch with Spitzer, because at that point in time no other man-made instrument was able to accomplish this feat.”

Another refinement of the model was to fold details about the physical properties of the larger black hole. In particular, its rotation.

Scientists, including the late Stephen Hawking, developed the so-called “no-hair” set of black holes. This essentially means that the surface or “event horizon” of a black hole is symmetrical along its axis of rotation – there are no lumps and bumps. No hair if you like.

The observation of OJ. 287 is said to be the best test for this idea so far. If there had been any serious irregularities, the predicted timing would not have worked so well.

Prof. Achamveedu Gopakumar from the Tata Institute of Fundamental Research, India, worked with PhD student Lankeswar Dey on adding gravitational waves to the model.

The professor spoke of his “high spirits” when he saw the Spitzer data coming through. He is now looking forward to seeing OJ 287 from the Event Horizon Telescope, which produced the first image of a black hole last year.

“The EHT has monitored the source in both 2017 and 2018. The other campaigns will be suspended (due to coronavirus) and we hope to have time during the 2021 campaign,” he told BBC News.

Details of the Spitzer observations are published in The Astrophysical Journal Letters.

The next flaring will be in 2022 and then in 2033 and 2034.

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