Astronomers have observed a black hole gradually consuming a star, providing a rare opportunity to predict the next cosmic “snack.”
This discovery offers valuable insights into black hole behavior and helps scientists refine models of these cosmic events.
The Fate of a Star Caught by a Black Hole
The survival of the star’s core after its initial close encounter with the black hole was an unexpected twist in this cosmic drama. Typically, when a star is caught by a black hole, it is destroyed in a single, violent event known as a tidal disruption event (TDE).
During a TDE, the star is torn apart by the immense gravitational forces, and its material is either absorbed by the black hole or ejected into space. In this case, however, the star’s core managed to survive the first pass, and instead of being completely destroyed, it continues to orbit the black hole. This has allowed astronomers to observe the black hole’s feeding behavior over an extended period, providing valuable data on how these events unfold over time.
According to Thomas Wevers of the Space Telescope Science Institute, "Initially, we thought this was a garden-variety case of a black hole totally ripping a star apart. Instead, the star appears to be living to die another day." This surprising survival has offered scientists a rare chance to witness a repeating partial tidal disruption event, where the black hole gradually consumes the star over multiple encounters.
Each time the star approaches the black hole, it loses more of its outer layers, which form a bright accretion disk as they are drawn in by the black hole’s gravitational forces. This process creates periodic flares that can be observed and studied by astronomers.
Predicting the Black Hole's Next Meal
Using data from the star's orbit and emissions recorded by telescopes, astronomers have been able to accurately predict when the black hole will next feast on the remaining material from the star. The star, named AT2018fyk, follows an elliptical orbit around the black hole, bringing it close enough to be stripped of its outer layers every 3.5 years.
These encounters create a bright flare of X-ray and ultraviolet light, which can be detected by telescopes such as Chandra, Swift, and XMM-Newton. In August 2023, astronomers confirmed their predictions when they observed a significant dimming of the star’s light, signaling that the black hole had consumed another portion of the star’s material.
Eric Coughlin, a professor of physics at Syracuse University, explained that the next encounter is expected to occur between May and August of 2025, when the black hole will likely feast again on the remnants of the star. "This will probably be more of a snack than a full meal," said Coughlin, referring to the fact that the star is being gradually whittled away with each encounter.
The ability to predict these cosmic events with such precision represents a major advancement in black hole research, allowing scientists to observe the ongoing interactions in real time and refine their models of black hole behavior.
The Mystery of a Star’s Survival
The star's survival is even more remarkable considering that it originally had a companion star. During the black hole encounter, this companion star was ejected into space at extraordinary speeds, traveling at approximately 1,000 kilometers per second (621 miles per second).
This violent separation left the surviving star bound to the black hole, while its companion escaped. Muryel Guolo of Johns Hopkins University explained the scenario: "The doomed star was forced to make a drastic change in companions—from another star to a giant black hole. Its stellar partner escaped, but it did not."
This unusual interaction between the black hole and the star provides an opportunity for scientists to explore new questions about stellar dynamics and the forces at play in extreme cosmic environments. The fact that the star continues to orbit the black hole and is being consumed gradually offers a unique glimpse into the feeding habits of black holes, which had previously been thought to devour stars in one swift action.
A Breakthrough in Black Hole Research
This discovery represents a major step forward in understanding black hole behavior and the complex interactions that occur when a star is caught in a black hole's gravitational grasp. By studying this black hole's "snacking" habits, researchers hope to develop more accurate models of how black holes consume stars and other matter in their vicinity. Coughlin added, "We anticipate that this model will be an essential tool for scientists in identifying these discoveries."
These findings not only provide insights into the life cycle of stars in the vicinity of black holes but also contribute to broader efforts to unravel the mysteries of black holes and their role in the universe. As more data is collected from telescopes such as Chandra and Swift, scientists are likely to gain an even deeper understanding of the mechanisms that drive these cosmic events.