Flash of Light Brighter Than a Trillion Stars Leads to Supermassive Black Hole Breakthrough

Caption for the Illustration: Artistic representation of OJ287, a binary black hole system, where a 150 million solar mass secondary black hole orbits an 18 billion solar mass primary black hole. The primary black hole is surrounded by a gas disk. The impact of the secondary black hole on the accretion disk generates a brilliant blue flash, detected in February 2022. Additionally, the secondary black hole emits bright bursts of radiation weeks before the impact. (Credit: AAS 2018)

Scientists Make First Direct Observation of Secondary Black Hole in OJ 287 Binary System

In a significant breakthrough, an international team of astronomers has successfully observed the presence of the second supermassive black hole in the active galaxy OJ 287.

The galaxy OJ287 has been the subject of intense study since 1888, and it is now revealed that it houses two supermassive black holes orbiting each other. The team’s observations have confirmed the long-standing hypothesis of a binary system by accurately detecting the predicted flares from these black holes. Notably, the secondary black hole was directly observed for the first time in 2021/2022, unveiling new types of flares. These findings position OJ287 as an excellent candidate for further investigation into gravitational waves.

Supermassive black holes, which weigh billions of times more than our Sun, reside at the centers of active galaxies. These cosmic giants are known for their luminous galactic cores, where matter from an accretion disk spirals into the supermassive black hole, creating a whirlpool of violent activity. Some of this matter is ejected as a powerful jet, resulting in the intense emission of electromagnetic radiation across the spectrum.

Recent studies have uncovered compelling evidence of two supermassive black holes in OJ287, based on signals originating from the jets associated with both black holes’ accretion processes. OJ287, also known as a quasar, represents a binary black hole system with the black holes positioned so close to each other that they appear as a single dot in the sky. However, by detecting distinct signals from each black hole, it becomes apparent that the dot consists of two separate entities.

To observe the orbital motion of the black holes, astronomers have closely monitored the series of flares produced when the secondary black hole periodically passes through the accretion disk of the primary black hole at speeds just below that of light. This interaction heats the disk material, causing the release of hot gas in the form of expanding bubbles. These bubbles take several months to cool down as they radiate energy, resulting in a dazzling flash of light—a flare—that persists for approximately two weeks and outshines a trillion stars.

After years of meticulous efforts to estimate the timing of the secondary black hole’s plunges through the accretion disk, astronomers from the University of Turku in Finland, led by Mauri Valtonen and Achamveedu Gopakumar from the Tata Institute of Fundamental Research in Mumbai, India, successfully modeled the orbit and accurately predicted the occurrence of these flares.

Through multiple observational campaigns conducted since 1983, with significant efforts in 1994, 1995, 2005, 2007, 2015, and 2019, the team has observed the predicted flares, thus confirming the existence of a supermassive black hole pair in OJ287.

“We have now witnessed a total of 26 predicted flares, and nearly all of them have been observed. The larger black hole in this pair exceeds the mass of our Sun by over 18 billion times, while its companion is approximately 100 times lighter. Their oblong orbit is not perfectly circular,” explains Professor Achamveedu Gopakumar.

However, until recently, astronomers had not directly detected any signals from the smaller black hole. Its existence had been inferred indirectly from the observed flares and the resulting wobbling of the jet emitted by the larger black hole.

“Due to their close proximity in the sky, the two black holes merge into a single point when observed through telescopes. Only by distinctly observing signals from each black hole can we confidently claim that we have truly ‘seen’ both of them,” says lead author Professor Mauri Valtonen.

Significant breakthrough: Direct observation of the smaller black hole

Excitingly, the observational campaigns carried out in 2021/2022 on OJ287, utilizing various types of telescopes, have enabled researchers to directly observe the secondary black hole’s plunges through the accretion disk and the resulting signals emitted by the smaller black hole itself.

“The 2021/2022 period holds special significance in the study of OJ287. We had predicted that during this time, the secondary black hole would plunge through the accretion disk of its more massive companion, resulting in a brilliant blue flash. As expected, this flash was observed within days of the predicted timeframe by Martin Jelinek and his colleagues at the Czech Technical University and Astronomical Institute of Czechia,” reveals Professor Mauri Valtonen.

Nevertheless, two intriguing surprises emerged from these observations—unprecedented types of flares that had never been detected before. The first of these flares was detected only through an extensive observation campaign conducted by Staszek Zola and his team at the Jagiellonian University of Cracow, Poland. This remarkable flare emitted light equivalent to a hundred times the brightness of an entire galaxy and lasted for just one day.

“According to estimates, the flare occurred shortly after the smaller black hole ingested a massive amount of new gas during its plunge. This ingestion process triggers the sudden brightening of OJ287. It is believed that this process also energizes the jet emanating from the smaller black hole in OJ287. While this event was predicted a decade ago, its confirmation has eluded us until now,” explains Valtonen.

The second unexpected signal was detected in the form of gamma rays, observed by NASA’s Fermi telescope. The most substantial gamma-ray flare in OJ287 in six years coincided with the smaller black hole’s plunge through the primary black hole’s gas disk. The interaction between the smaller black hole’s jet and the disk gas leads to the production of gamma rays. To substantiate this notion, the researchers verified that a similar gamma-ray flare occurred in 2013 when the small black hole previously passed through the gas disk, as viewed from the same vantage point.

“Why haven’t we seen this one-day burst before? OJ287 has been extensively photographed since 1888 and intensively monitored since 1970. It turns out that we were simply unlucky. No one observed OJ287 precisely during the nights when this extraordinary event unfolded. Without the diligent surveillance by Zola’s group, we would have missed it this time as well,” remarks Valtonen.

These efforts establish OJ287 as the most promising candidate for a supermassive black hole pair generating gravitational waves at nano-hertz frequencies. Additionally, OJ287 is being regularly monitored by both the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA) consortia to search for further evidence of a supermassive black hole pair at its center. These observations aim to capture a radio image of the secondary jet.

The detailed results of this study will be published in the June 2023 issue of Monthly Notices of the Royal Astronomical Society.

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More about supermassive black holes

• “Monthly Notices of the Royal Astronomical Society” – Link
• “AAS 2018” – Link (American Astronomical Society)
• Event Horizon Telescope (EHT) – Link
• Global mm-VLBI Array (GMVA) – Link
• NASA’s Fermi Gamma-ray Space Telescope – Link
• Swift ultraviolet to x-ray telescope – Link
• University of Turku – Link
• Tata Institute of Fundamental Research – Link
• Czech Technical University – Link
• Astronomical Institute of Czechia – Link
• Jagiellonian University of Cracow – Link
• Aalto University – Link