Decades of radio astronomy data reside in the archives of the National Radio Astronomy Observatory (NRAO), and new discoveries are still lurking within it. Astronomers discovered the distinctive jet emanating from a star-devouring black hole decades ago in archival data collected by the Very Large Array (VLA) telescope in New Mexico. According to a new research paper published in The Astrophysical Journal, this is the second candidate event detected in the radio system; The first was discovered in 2020. The discovery was presented approximately yesterday at a meeting of the American Astronomical Society.
As mentioned earlier, it is a common misconception that black holes behave like cosmic vacuum cleaners, sucking hard at any matter in their surroundings. In fact, only things beyond the event horizon – including light – are swallowed up and cannot escape, although black holes are also chaotic eaters. This means that part of the body substance is already expelled in a strong jet.
If this object is a star, then the process of its tearing (or “ripping”) by the black hole’s strong gravitational forces occurs outside the event horizon, and a portion of the star’s original mass is violently ejected outward. This, in turn, can form a rotating ring of matter (also known as an accretion disk) around the black hole that emits powerful X-rays and visible light – and sometimes radio waves. These jets are one way astronomers can indirectly infer the existence of a black hole. They are known as “tidal disturbance events” (TDEs).
For example, in 2018, astronomers announced the first direct image of the fallout from a star torn apart by a black hole 20 million times larger than our sun. The encounter occurred in a pair of colliding galaxies called Arp 299, 150 million light-years from Earth. Astronomers have used a range of radio and infrared telescopes, including the Very Long Baseline Array (VLBA), to follow the formation and expansion of the jet of matter. Matter was expelled after a star was torn apart by a supermassive black hole at the center of one of the colliding galaxies.
Astronomers found another TDE in 2020 (dubbed AT 2019qiz), which provided the first direct evidence that gas flowing during turbulence and accretion produces strong light and radio emissions previously observed.
However, these powerful bursts of light are often hidden behind a veil of interstellar dust and debris, making it difficult for astronomers to detect them or study them in greater detail with optical or X-ray telescopes. “This study demonstrates the power of radio surveys in detecting TDEs,” said co-author Vikram Ravi of the California Institute of Technology, by capturing powerful jets shining in the radiofrequency system. The events are potentially powerful tools for studying the inner workings of black holes.
The new TDE filter has been named J1533+2727. Two Raffy’s high school intern first discovered it when he was a postdoctoral researcher at Harvard University. Looking through the archives, they noticed that an image of a bright radio object taken in the mid-1990s had faded significantly by 2017. They found images of the same object in the archives of the 300-foot Green Bank Telescope, which showed the object was much brighter in 1986/1987.
Further bolstered by new observations by the VLA, Ravi and his team concluded that the object was a TDE – the result of a supermassive black hole at the center of a galaxy about 500 million light-years away that devoured a star and ejected a powerful radio jet traveling at close to the speed of light. The discovery is being published jointly with astronomers at the University of Toronto, who also independently found the object.
It’s the closest example of this type of TDE filter to date, suggesting that such radio bright events may be more common than astronomers previously thought. Ravi’s group has already spotted another possible radioactive TDE using the VLA, although it may also be a glow from an active supermassive black hole.