Cosmic mechanism decoded in black hole feeding patterns

Black holes, previously elusive and invisible, have been revealed by observing tidal disruption events (TDEs), where stars are violently destroyed, generating bright flares that can be observed across vast distances.

The dramatic dimming of the light source is confirmed about 860 million light-years from Earth. accuracy From a detailed model developed by a team of astrophysicists from Syracuse University, Massachusetts Institute of Technologyand Space Telescope Science Institute.

Understanding Black Holes Through TDEs

Powerful telescopes like NASAThe Hubble, James Webb and Chandra X-ray observatories provide scientists with a window into deep space to explore the physics of black holes. While one might wonder how you can “see” a black hole, Black holeStars that suck up all the light are made possible by tidal disruption events (TDEs) – where a star is destroyed by a supermassive black hole and can fuel a “luminous accretion flare.” With their luminosity thousands of billions of times brighter than the Sun, TDEs enable astrophysicists to study supermassive black holes (SMBHs) at cosmic distances.

TDEs occur when a star is violently torn apart by the immense gravitational field of a black hole. As the star is torn apart, its remains are transformed into a stream of debris that rains back down onto the black hole, forming an extremely hot, bright disk of material orbiting the black hole, called an accretion disk. Scientists can study this phenomenon to make direct observations of TDEs and compare them to theoretical models to link the observations to the physical properties of the torn apart stars and the torn apart black holes.

Innovations in Black Hole Research

A team of physicists from Syracuse University, MIT, and the Space Telescope Science Institute used detailed modeling to predict the brightening and dimming of AT2018fyk, a recurring partial TDE, meaning that the star’s dense core survived the gravitational interaction with the SMBH, allowing it to orbit the black hole and be torn apart more than once.

The model predicted that AT2018fyk would “fade” in August 2023, a prediction that was confirmed when the source disappeared last summer, providing evidence that their model offers a new way to explore the physics of black holes. Their results are published in the journal Nature. the Astrophysical Journal Letters.

High energy source

Thanks to incredibly detailed galactic surveys, scientists are watching more light sources come and go than ever before. The surveys scan entire hemispheres of the Earth, looking for sudden brightening or dimming of sources, which tells researchers that something has changed. Unlike the telescope in your living room, which can only focus visible light, telescopes like Chandra can detect light sources in what’s known as the X-ray spectrum, emitted by matter at temperatures of millions of degrees.

Visible light and X-rays are both forms of electromagnetic radiation, but X-rays have shorter wavelengths and more energy. Similar to the way your stove gets “red hot” after you turn it on, the gas that makes up the disk “glow” at different temperatures, with the hottest material being closer to the black hole. However, instead of radiating its energy at optical wavelengths that are visible to the eye, the hottest gas in the accretion disk emits its energy in the X-ray spectrum. These are the same X-rays that doctors use to image your bones and that can pass through soft tissue, and because of this relative transparency, the detectors used by NASA’s X-ray telescopes are specially designed to detect this high-energy radiation.

Repeated performance

In January 2023, a team of physicists, including Eric Coughlin, a professor in the Department of Physics at Syracuse University, Dheeraj R. “DJ” Basham, a research scientist at MIT, and Thomas Wevers, a fellow at the Space Telescope Science Institute, published a paper in Astrophysical Journal Letters This team has proposed a detailed model for the partial TDE recurrence. Their results are the first to map the orbit of a sudden star returning around a supermassive black hole – and reveal new information about one of the most extreme environments in the universe.

The team based their study on a TDE phenomenon known as AT2018fyk (AT stands for “transient astrophysical phenomena”), which suggested that a star had been captured by a supermassive black hole through an exchange process known as “hills capture.” Originally, one of the stars was part of a binary system (two stars orbiting each other under their mutual gravity), and it was hypothesized that one star had been captured by the black hole’s gravitational field while the other (non-captured) star was ejected from the galactic center at speeds similar to ~1000 km/s.

Once bound to the supermassive black hole, the star powering the emission from AT2018fyk is repeatedly stripped of its outer shell each time it passes closest to the black hole. The stripped outer layers of the star form a bright accretion disk, which researchers can study using X-ray and ultraviolet/optical telescopes that observe light from distant galaxies.

While TDEs are usually “one-offs” because the supermassive black hole’s intense gravitational field destroys the star, meaning the supermassive black hole fades back into darkness after the accretion glow, AT2018fyk provided a unique opportunity to explore a recurring partial TDE.

The research team used three telescopes to make the initial and follow-up discoveries: Swift and Chandra, both operated by NASA, and XMM-Newton, a European mission. AT2018fyk was first spotted in 2018 and is about 860 million light-years away, meaning that because of the time it takes light to travel, it happened in “real time” about 860 million years ago.

The team used detailed models to predict that the light source will suddenly disappear around August 2023, then brighten again when newly stripped matter converges on the black hole in 2025.

Exploring the Future: Prospects and Implications

Confirming the accuracy of their model, the team reported a decrease in X-ray flux over a two-month period, starting on August 14, 2023. This sudden change can be interpreted as a second shutdown of the emission.

“The observed emission closure shows that our model and assumptions are valid, and suggests that we are indeed seeing a star slowly being devoured by a distant, supermassive black hole,” says Coughlin. “In our paper last year, we used constraints from the initial outburst, dimming, and re-brightening to predict that AT2018fyk should show a sudden, rapid dimming in August 2023, if The star survived the second encounter, which led to the second flare.

The fact that the system showed this expected closure suggests several distinctions between a star and a black hole:

• The star survived its second encounter with the black hole;
• The rate at which stripped debris returns to the black hole is closely related to the brightness of AT2018fyk;
• The star’s orbital period around the black hole is about 1,300 days, or about 3.5 years.

The second cutoff indicates that another re-brightening should occur between May and August 2025, and if the star survives the second encounter, a third cutoff is expected between January and July 2027.

As for whether we can count on seeing a re-brightening in 2025, Coughlin says the discovery of the second cut means the star has recently been stripped of more mass, which must return to the black hole to produce a third brightening.

“The only uncertainty is the peak of the emission,” he says. “The second re-brightening peak was much weaker than the first, and unfortunately the third burst could be even weaker. That’s the only thing that might limit the possibility of detecting this third burst.”

Coughlin notes that this model represents an exciting new way to study the occurrence of extremely rare partial TDEs, which are thought to occur once every million years in a given galaxy. So far, he says, scientists have encountered only four or five systems that exhibit this behavior.

“With the advent of improved detection technology that reveals more recurring partial TDEs, we expect this model to be an essential tool for scientists in identifying these discoveries,” he says.

Reference: “A Possible Second Shutdown of AT2018fyk: An Updated Orbital Calendar for the Surviving Star under the Recurring Partial Tidal Disruption Event Model” by Dheeraj Basham, E. R. Coughlin, M. Gullo, T. Wevers, C. J. Nixon, Jason T. Hinkle, and A. Bandopadhyay, 14 August 2024, Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/ad57b3