NASA Telescopes Illuminate Black Hole's Feeding Schedule

Recent findings from NASA's Chandra X-ray Observatory, the Neil Gehrels Swift Observatory, and ESA's XMM-Newton focus on a supermassive black hole’s feeding timing and process. A research paper is available on the arXiv preprint server and will be published in The Astrophysical Journal. Key researchers include Dheeraj Pasham (Massachusetts Institute of Technology), Eric Coughlin (Syracuse University), Muryel Guolo (Johns Hopkins University), and others.

An artist's rendition above illustrates a star perturbed by a black hole in the AT2018fyk system. This supermassive black hole, about 50 million times the mass of the sun, resides in a galaxy approximately 860 million light-years from Earth.

Astronomers identified that a star orbits the black hole with a highly elliptical path. The star's farthest distance from the black hole significantly exceeds the closest point. During its closest approach, tidal forces cause the black hole to extract material from the star. This results in two tidal tails composed of "stellar debris."

The illustration depicts a timeline in the star's orbit after it experiences partial destruction. At this stage, the tidal tails remain close to the star. In following orbits, the disrupted material revisits the black hole and loses energy. This leads to an increase in X-ray brightness occurring later in the star’s trajectory.

A cycle occurs every 3.5 years, with the illustration showing the star during its second orbit. The accompanying disk of X-ray emitting gas around the black hole arises from the first tidal interaction.

In 2018, the AT2018fyk system appeared significantly brighter, prompting astronomers’ interest. The optical ground-based survey ASAS-SN detected this brightness surge. Subsequent observations using NASA's NICER and Chandra, along with XMM-Newton, indicated a "tidal disruption event" or TDE—signifying the star was torn apart and partially consumed after nearing the black hole.

When the star’s material drew close to the black hole, it emitted X-ray and ultraviolet (UV) light. These emissions later subsided, suggesting no remaining material was edible for the black hole. However, two years later, the X-ray and UV emissions intensified anew. Astronomers surmised the star survived the initial encounter with the black hole. It entered an elliptical orbit, leading to further material loss during a subsequent close approach.

These findings were published in a 2023 Astrophysical Journal Letters article led by Thomas Wevers. Wevers noted, "Initially, we thought this phenomenon indicated a star has been entirely devoured. Instead, it seems the star will survive to encounter danger again."

Given insights about the star's movements, Wevers and the research team projected that the black hole would have another opportunity to feed in August 2023. They secured observing time with Chandra to investigate.

Dheeraj Pasham, leader of the new paper, observed a sudden decrease in X-rays on August 14, 2023, signaling the conclusion of the stellar feast. "Our data confirms that, at this time, the black hole seemed to wipe its mouth and push back from the table," he explained.

The updated data from Chandra and Swift further refines the orbital timeline, setting expectations for future feeding events of the black hole. The team estimates the star nears the black hole approximately every 3.5 years.

Eric Coughlin, co-author from Syracuse University, mentioned, "A potential third meal could occur between May and August of 2025 and may last nearly two years." He anticipates this might be a smaller feeding, suggesting that the star's vitality diminishes with each encounter.

It is believed the ill-fated star initially had a companion. As they approached the black hole, the latter’s gravitational pull separated them. One star remained in the black hole’s orbit, while the other was propelled into space.

Muryel Guolo of Johns Hopkins University remarked, "This star has undergone a drastic change of companionship—from another star to a giant black hole. Its companion escaped, but it did not."

The research team intends to closely monitor AT2018fyk to better understand this unique cosmic system.

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