An international team of astronomers just found that a presumed supernova is actually something much rarer.

Astronomers, led by Anna Payne of the University of Hawai’i at Mānoa, just found that a presumed supernova is actually periodic flaring from a black hole in a distant galaxy.

An active galactic nucleus (AGN) in the center of ESO 253-G003 erupts approximately every 114 days. The black hole gives off bursts of energy as it tears off chunks of an orbiting star.

An active galactic nucleus is a compact region at the center of a galaxy. It is basically the core of a galaxy. It’s typically highly variable and very bright relative to the rest of the galaxy. This central region radiates huge luminosity over the electromagnetic spectrum. Likely, the gravitational pull of a supermassive black hole at the center of the host galaxy which drags matter inward causes the radiation from an AGN.

However, the active galaxy lies over 570 million light-years away in the southern constellation of Pictor.

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Scientists first discovered the phenomenon, called ASASSN-14ko, on November 14, 2014, using the All-Sky Automated Survey for Supernovae (ASAS-SN).

ASAS-SN is a global network of 20 robotic telescopes headquartered at The Ohio State University (OSU) in Columbus.

“ASASSN-14ko is currently our best example of periodic variability in an active galaxy, despite decades of other claims, because the timing of its flares is very consistent over the six years of data,” said Dr. Jeremy Schnittman, an astrophysicist at NASA’s Goddard Space Flight Center who was not involved in the study.

“This result is a real tour de force of multiwavelength observational astronomy.”

Such active galaxies have unusually bright and variable centers. These bodies produce much more energy than the combined contribution of all their stars. This might be due to gravitational and frictional forces heating a swirling disk of gas and dust that accumulates around the central supermassive black hole. As the matter slowly falls into the black hole it creates random changes in the light emitted by the disk.

Looking at the ESO 253-3 light curve, or the graph of its brightness over time, Payne and colleagues noticed a series of 17 flares, all separated by about 114 days. Each flare reaches its peak brightness in about five days, then steadily dims.

Based on this discovery, the researchers suggested that the galaxy would experience another burst on May 17 of last year. Thus, they coordinated ground- and space-based facilities to make observations. They have since successfully predicted and witnessed flares on September 7 and December 26.

They also used data from NASA’s Transiting Exoplanet Survey Satellite (TESS) to create a precise timeline of a flare that began on November 7, 2018, tracking its emergence, rise to peak brightness, and decline in great detail.

What Causes The Repeated Flares?

Using measurements from ASAS-SN, TESS, Swift, and other observatories, including NASA’s NuSTAR and ESA’s XMM-Newton observatories, the researchers came up with three possible explanations for the repeating flares.

One less-likely possibility included interactions between the disks of two orbiting supermassive black holes at the center of ESO 253-G003.

Based on recent measurements, the galaxy does indeed host two such objects. But they don’t orbit close enough to produce this frequency of flares.

The other scenario involved a star passing on an inclined orbit through a black hole’s disk. In that case, they would expect to see asymmetrically shaped flares caused when the star disturbs the disk twice, on either side of the black hole. But the flares from this galaxy all have the same shape.

And lastly, the most likely scenario is what astronomers call a partial tidal disruption event or TDE.

TDEs occur when an orbiting star gets too close to a supermassive black hole, which sheds its mass but doesn’t destroy it. Instead, every approach strips away an amount of gas equal to about three times the mass of Jupiter.

The flares occur when the lost material falls into the black hole.

“We think a supermassive black hole at the galaxy’s center creates the bursts as it partially consumes an orbiting giant star,” said lead author Anna Payne.

Scientists revealed their findings—based on 20 instances of regular outbursts—in a paper published in the Astrophysical Journal.

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