Understanding Black Holes Through TDEs Powerful telescopes like NASA’s Hubble, James Webb, and Chandra X-ray Observatory provide scientists a window into deep space to probe the physics of black holes.
As the star is shredded, its remnants are transformed into a stream of debris that rains back down onto the black hole to form a very hot, very bright disk of material swirling around the black hole, called an accretion disc.
Scientists can study these to make direct observations of TDEs, and compare those to theoretical models to relate observations to physical properties of disrupted stars and their disrupting black holes.
Similar to the way in which your stove becomes “red hot” after you turn it on, the gas comprising a disc “glows” at different temperatures, with the hottest material closest to the black hole.
Their results were the first to map a star’s surprising return orbit about a supermassive black hole – revealing new information about one of the cosmos’ most extreme environments.
The long-mythologized, enigmatic nature of black holes is being revealed by the observation of tidal disruption events (TDEs), in which stars are violently destroyed and produce bright flares visible over great distances.
The sharp decrease in brightness of a light source approximately 860 million light-years from Earth validates the precision of an intricate model created by a group of astrophysicists from Syracuse University, Massachusetts Institute of Technology, and the Space Telescope Science Institute.
TDEs: A Framework for Understanding Black Holes.
Strong telescopes that allow scientists to study the physics of black holes in deep space include NASA’s Hubble, James Webb, and Chandra X-ray Observatory. Although a black hole is known to absorb all light, it is possible to “see” one thanks to a phenomenon known as tidal disruption events (TDEs), in which a star is destroyed by a supermassive black hole and the energy released is used to create a “luminous accretion flare.”. “Accretion events allow astrophysicists to study supermassive black holes (SMBHs) at cosmological distances because of their luminosities, which are thousands of billions of times brighter than the Sun.”.
TDEs happen when a black hole’s strong gravitational field violently tears apart a star. The remnants of the shredded star become a stream of debris that rains back down onto the black hole, forming an accretion disc—a very hot, very bright disk of material that swirls around the black hole. Researchers can use these to observe TDEs directly and then correlate observations with theoretical models to determine the physical characteristics of disrupted stars and the black holes that cause them.
Novelties in Research on Black Holes.
AT2018fyk is a repeating partial TDE, meaning that the star’s high-density core survived the gravitational interaction with the black hole, allowing it to orbit the black hole and be repeatedly destroyed. This was predicted by a team of physicists from Syracuse University, MIT, and the Space Telescope Science Institute using meticulous modeling.
When AT2018fyk went dark last summer, the model’s prediction that it would “dim” in August 2023 came true. This indicates that the model offers a fresh perspective on investigating the physics of black holes. The Astrophysical Journal Letters published their findings.
a Source of High Energy.
More incoming and outgoing light sources than ever before are being tracked by scientists thanks to extraordinarily detailed extragalactic surveys. Surveys cover the whole hemisphere looking for abrupt changes in source brightness or dimness, which indicates to scientists that something has changed. Telescopes like Chandra can identify light sources in the so-called X-ray spectrum, which is emitted by materials that are millions of degrees hotter than your living room telescope, which can only focus visible light.
X-rays and visible light are both types of electromagnetic radiation, but X-rays are more energetic and have shorter wavelengths. The gas inside a disc “glows” at different temperatures, with the hottest material closest to the black hole. This is similar to how your stove gets “red hot” when you turn it on. The hottest gas in an accretion disc, however, emits in the X-ray spectrum rather than at optical wavelengths that are visible to the human eye. Since these X-rays can penetrate soft tissue and are the same ones that doctors use to image your bones, NASA X-ray telescopes have detectors made expressly to pick up on this high-energy radiation. ‘.
An Repeat Show.
A group of physicists, led by Thomas Wevers, a Fellow at the Space Telescope Science Institute, Dheeraj R. “DJ” Pasham, a research scientist at MIT, and Eric Coughlin, a professor at Syracuse University’s Department of Physics, published a paper in The Astrophysical Journal Letters in January 2023 proposing a comprehensive model for a repeating partial TDE. Their findings were the first to map a star’s unexpected return orbit around a supermassive black hole, providing fresh insight into one of the harshest environments in the universe.
Based on a TDE known as AT2018fyk (AT stands for “Astrophysical Transient”), the team examined how a star might be captured by a supermassive black hole (SMBH) using a process known as “Hills capture.”. One of the stars, which were initially part of a binary system (two stars orbiting each other due to their mutual gravitational attraction), was thought to have been captured by the black hole’s gravitational field, while the other star, which was not captured, was expelled from the galaxy’s center at velocities of up to about 1000 km/s.
The star driving the emission from AT2018fyk was once bound to the SMBH, but every time it passes through the point where the black hole and star are closest, the star is repeatedly deprived of its outer envelope. Using X-ray and ultraviolet/optical telescopes that observe light from far-off galaxies, scientists can study the bright accretion disk, which is made up of the star’s stripped outer layers.
AT2018fyk provided the rare chance to investigate a repeating partial TDE, whereas TDEs are typically “once-and-done” because the SMBH’s strong gravitational field destroys the star, causing the SMBH to fade back into darkness after the accretion flare.
To make the first and subsequent detections, the research team used three telescopes: the European mission XMM-Newton, the NASA telescopes Chandra and Swift. When AT2018fyk was first detected in 2018, it was approximately 860 million light-years away. This means that, due to the time it takes for light to travel, it occurred in “real-time” about 860 million years ago.
Using sophisticated modeling, the team predicted that the light source would suddenly vanish in August 2023 and reappear in 2025 when the newly stripped material accretes onto the black hole.
Examining the Future: Forecasts and Consequences.
The team reported a two-month drop in X-ray flux beginning on August 14, 2023, confirming the accuracy of their model. It is possible to interpret this abrupt change as the second emission shutdown.
“Our model and assumptions are valid, and the observed emission shutoff indicates that we are actually witnessing the slow annihilation of a star by a far-off, massive black hole,” Coughlin says. Based on constraints from the first outburst, dimming, and rebrightening, we predicted in our paper from the previous year that, if AT2018fyk survives the second encounter that triggers the second brightening, it will exhibit an abrupt and rapid dimming in August 2023. “.
The system’s display of this anticipated shutdown suggests a few differences between the black hole and the star.
After meeting the black hole a second time, the star lived.
The brightness of AT2018fyk and the rate at which stripped debris returns to the black hole are closely related.
and the star’s orbital period around the black hole is approximately 1300 days, or 3.5 years.
If the star survives the second encounter, a third shutoff is anticipated to take place between January and July of 2027. The second cutoff suggests that another rebrightening should occur between May and August of 2025.
Regarding whether we should expect a rebrightening in 2025, Coughlin says that the finding of a second cutoff suggests that the star has had more mass recently stripped, which should cause a third brightening to occur, returning to the black hole.
“The emission peak is the only area of uncertainty,” he states. “The second re-brightened peak was noticeably less bright than the first, and the third eruption may, regrettably, be even less bright. Only this would restrict this third outburst’s detectability. “.
This model, according to Coughlin, represents an exciting new avenue for research into the extremely rare repeating partial TDE events, which are thought to occur once every million years in a given galaxy. According to him, only four or five systems have shown this behavior in scientific studies to date.
He states, “We anticipate that this model will be an essential tool for scientists in identifying these discoveries with the advent of improved detection technology uncovering more repeating partial TDEs.”.
