International Team of Scientists Explains Persistent Hiccups in Black Hole at the Centre of Far-Off Galaxy

Astronomers caught a tiny black hole repeatedly punching through a larger black hole’s disk of gas.

In a groundbreaking discovery, astronomers have observed a peculiar phenomenon at the heart of a distant galaxy that has left scientists confused. The discovery, made by an international team of researchers, including scientist from the Aryabhatta Research Institute of observational sciencES (ARIES), an autonomous institute of the Department of Science & Technology (DST), Govt. of India, sheds light on previously unseen behaviour in black holes.

Located approximately 800 million light-years away, a supermassive black hole at the center of this far-off galaxy has exhibited what scientists call “persistent hiccups.” These hiccups manifest as periodic bursts of gas emissions every 8.5 days, followed by a return to its normal, dormant state.

This unprecedented behavior challenges the conventional understanding of black hole accretion disks, previously thought to be relatively uniform structures rotating around central black holes. Dr. Dheeraj Pasham, the lead author of the publication and a research scientist at MIT’s Kavli Institute for Astrophysics and Space Research, remarked, “We thought we knew a lot about black holes, but this is telling us there are a lot more things they can do.” 

Findings of the team, which included Dr. Suvendu Rakshit from ARIES for estimating the mass of the central supermassive black hole and contributing significantly for the interpretation of the new phenomena, published in the journal of Science Advances, propose an intriguing explanation for these periodic outbursts. It is believed that a smaller black hole orbits the central supermassive black hole, periodically disrupting its disk of gas and releasing gas plumes in the process. This discovery suggests that accretion disks may contain diverse objects, including other black holes and even entire stars. “We were surprised to see this phenomena, explaining the behaviour took a lot of effort,” says Dr. Rakshit.

The discovery was made possible by the Automated Survey for SuperNovae (ASAS-SN), a network of robotic telescopes that detected a burst of light in a distant galaxy. Dr. Pasham, who noticed the detection, utilized NASA’s Neutron star Interior Composition Explorer (NICER) to closely monitor the galaxy’s X-ray emissions during the outburst.

The team found that the galaxy was relatively quiet prior to the December 2020 detection. Dr. Rakshit found the central supermassive black hole of the galaxy is as massive as 50 million suns. Prior to the outburst, the black hole may have had a faint, diffuse accretion disk rotating around it, as a second, smaller black hole, measuring 100 to 10,000 solar masses, was orbiting in relative obscurity.

The researchers suspect that, in December 2020, a third object — likely a nearby star — swung too close to the system and was shredded to pieces by the supermassive black hole’s immense gravity — an event that astronomers know as a “tidal disruption event.” The sudden influx of stellar material momentarily brightened the black hole’s accretion disk as the star’s debris swirled into the black hole. Over four months, the black hole feasted on the stellar debris as the second black hole continued orbiting. As it punched through the disk, it ejected a much larger plume than it normally would, which happened to eject straight out toward NICER’s scope.

Figure 1: A computer simulation of an intermediate-mass black hole orbiting a supermassive black hole. During each orbit the small black hole punches through the accretion disk surrounding the big black hole like a car ploughing through a pile of leaves, and pushes gas towards the big black hole's spin axis. The magnetic field there acts as a leaf blower and launches blobs of gas moving at 30 percent the speed of light that temporarily blocks the million degree hot X-rays coming from the edge of the event horizon of the supermassive black hole.

Further analysis revealed a curious pattern of dips in the X-ray emissions occurring every 8.5 days, indicating the presence of a secondary black hole punching through the disk. Collaborating with theoretical physicists from the Czech Republic, the team conducted simulations that supported this hypothesis, suggesting the existence of a David-and-Goliath-like system where a smaller black hole orbits a larger one.

“This is a different beast,” remarked Dr. Pasham. “It challenges the traditional picture of a simple gaseous disk around black holes.” The implications of this discovery extend beyond the individual galaxy studied, hinting at the possibility of a vast population of similar systems waiting to be uncovered. “High cadence monitoring is essential to catch such remarkable events and we expect more such events in future,” said Dr. Rakshit.

Figure 2: An intermediate-mass black hole orbiting a supermassive black hole, and driving periodic gas plumes that can explain the observations.

As astronomers continue to unravel the mysteries of the universe, this discovery serves as a reminder of the boundless complexity and diversity of cosmic phenomena, challenging our understanding and inspiring new avenues of research.

Publication: Pasham et al., 2024, Science Advances

Publication Link: https://dx.doi.org/10.1126/sciadv.adj8898

For more details, Dr. Suvendu Rakshit may be contacted by email on suvendu[at]aries[dot]res[dot]in