Earlier this year, the Very Large Telescope of the European Southern Observatorylocated in Cerro Paranal, Antofagasta, was alerted after a survey telescope will detect an unusual source of visible light. The VLT, along with other telescopes, quickly repositioned itself toward the source: a supermassive black hole in a distant galaxy that had gobbled up a star, spewing the debris out in a jet.
The telescope determined that it was the furthest example of such an event ever observed. Because the jet is pointed almost towards us, this is also the first time it has been discovered in visible light, providing a new way to detect these extreme events. This research was presented in an article titled “A very luminous jet from the disruption of a star by a massive black hole”, published in the scientific journal Nature.
Stars that wander too close to a black hole are torn apart by the incredible tidal forces of the black hole in what is known as a tidal disruption event (TDE). About 1% of these cause the ejection of plasma and radiation jets from the poles of the rotating black hole. In 1971, black hole pioneer John Wheeler introduced the concept of a TDE jet as “a tube of toothpaste squeezed in the middle,” causing the system to “blow matter out of both ends.”
“We’ve only seen a handful of these jet TDEs and they’re still very exotic and poorly understood events,” says Nial Tanvir of the University of Leicester in the UK, who led the observations to determine the object’s distance from the VLT. Therefore, astronomers constantly look for these extreme events to understand how the jets are actually created and why such a small fraction of TDE produces them.
As part of this search, many telescopes, including the Zwicky Transient Facility (ZTF) in the US, repeatedly scan the sky for signs of short duration, often extreme, which could then be studied in much more detail by telescopes such as the VLT of that. in Chile. “We developed an open source data pipeline to store and extract important information from the ZTF survey and alert us to outlier events in real time,” explains Igor Andreoni, an astronomer at the University of Maryland, who co-led the paper with Michael Coughlin of the University of Minnesota.
In February this year ZTF detected a new visible light source. The event, called AT2022cmc, was reminiscent of an outburst of gamma rays, the most powerful light source in the Universe. The prospect of witnessing this rare phenomenon led astronomers to activate several telescopes around the world to observe the mysterious source in more detail. This included the ESO VLT, which quickly observed this new event with the instrument X shooter. The VLT data located the source at an unprecedented distance for these events: the light produced by AT2022cmc began its journey when the universe was about a third of its current age.
A wide variety of light, from high-energy gamma rays to radio waves, was collected by 21 telescopes around the world. The team compared this data with different types of known events, from the collapse of stars to kilonovae. But the only scenario that matched the data was a rare TDE thrown at us. Giorgos Leloudas, an astronomer at DTU Space in Denmark and co-author of this study, explains that “because the relativistic jet is pointing at us, makes the event much brighter than it would appear otherwise, and visible over a broader span of the electromagnetic spectrum.
The VLT distance measurement found AT2022cmc to be the most distant TDE ever discovered, but this is not the only record-breaking appearance of this object. “Until now, the small number of jet TDEs that are known were initially detected using high-energy X-ray and gamma-ray telescopes, but this was the first discovery of one during an optical survey,” says Daniel Perley, an astronomer from Liverpool. John Moores University in the UK. This demonstrates a new way to detect jet TDE, allowing further study of these rare events and probing the extreme environments surrounding black holes.