Astronomers Track Star's Repeated Encounters with Supermassive Black Hole

Astronomers Track Star's Repeated Encounters with Supermassive Black Hole
by Clarence Oxford
Los Angeles CA (SPX) Aug 15, 2024

Using data from NASA's Chandra X-ray Observatory, the Neil Gehrels Swift Observatory, and ESA's XMM-Newton, researchers have gained significant insights into the timing and process of how a supermassive black hole consumes material, as detailed in a recent study.

An artist's impression illustrates a star being partially disrupted by a black hole in the system known as AT2018fyk. This black hole, approximately 50 million times more massive than the sun, is located at the center of a galaxy around 860 million light-years from Earth.

Astronomers have determined that the star orbits the black hole in a highly elliptical path, where its distance from the black hole varies greatly. As the star comes closer, the black hole's tidal forces strip away material, creating two streams of stellar debris.

The illustration captures a moment shortly after the star has been partially torn apart, with the debris streams still close by. Later in the star's orbit, the material falls back towards the black hole, loses energy, and results in a significant increase in X-ray brightness. This sequence repeats approximately every 3.5 years when the star reaches its closest point to the black hole. The artist's depiction shows the star during its second orbit, surrounded by a disk of X-ray emitting gas, which formed from the first encounter.

Researchers first noticed AT2018fyk in 2018 when the ground-based ASAS-SN survey detected a brightening of the system. Subsequent observations using NICER, Chandra, and XMM-Newton revealed that this brightness was due to a "tidal disruption event" (TDE), where a star is torn apart after coming too close to a black hole. The Chandra data of AT2018fyk are shown in an inset within an optical image of a larger field.

When the star's remnants neared the black hole, they heated up and emitted X-ray and ultraviolet (UV) light, which then dimmed as the material was consumed. However, about two years later, the X-ray and UV light from the galaxy brightened again. This indicated that the star had survived its initial encounter with the black hole and entered a highly elliptical orbit. On its second close approach, more material was stripped off, generating another burst of X-ray and UV light.

Based on these observations, astronomers predicted that the black hole's feeding would conclude by August 2023 and scheduled Chandra to observe the event. Indeed, Chandra's observations on August 14, 2023, confirmed a sudden drop in X-ray emissions, signaling the end of this cosmic meal. The team also refined their estimates of the star's orbital period and forecasted future feeding events.

The findings are published in the August 14, 2024 issue of 'The Astrophysical Journal'. The study was conducted by a team including Dheeraj Passam (Massachusetts Institute of Technology), Eric Coughlin (Syracuse University), Muryel Guolo (Johns Hopkins University), Thomas Wevers (Space Telescope Science Institute), Chris Nixon (University of Leeds, UK), Jason Hinkle (University of Hawaii at Manoa), and Ananaya Bandopadhyay (Syracuse).

NASA's Marshall Space Flight Center oversees the Chandra program, with science managed by the Smithsonian Astrophysical Observatory's Chandra X-ray Center from Cambridge, Massachusetts, and flight operations based in Burlington, Massachusetts.