Colossal explosion as distant 'super sun' shredded by black hole

A black hole has shredded a massive star like it was “preparing a snack for lunch”, according to a team of scientists at the American Astronomical Society's annual meeting (5 to 8 January).

The cosmic mismatch was witnessed by astronomers around the world and reported at the AAS conference in Phoenix, Arizona, where the unfortunate star was described as “torn up” and devoured bit by bit by the huge gravity of the black hole.

Associate Professor of Astrophysics Daniel Perley, of Liverpool John Moores University, lead author of a paper to the Monthly Notices of the Royal Astronomical Society, told the conference: “We discovered what we think is a black hole merging with a massive companion star, shredding it into a disk that feeds the black hole.  It’s a rare and awe-inspiring phenomenon.”

The resulting explosion is one of the most powerful cosmic events in history: the amount of energy being released briefly reached 400 billion times that of Earth’s Sun, and exceeded even the most powerful known supernovae.

'Unsurpassed scale'

Black holes have been observed before to appear to be devouring stars – a phenomenon known as a Tidal Disruption Event - but nothing on such as scale as this.

Anna Ho, an assistant professor of astronomy at Cornell University and co-author of Perley on the paper, identified the spectacular event, designated AT2024wpp and nicknamed the Whippet, almost immediately after its light reached us using the Zwicky Transient Facility, at Palomar Observatory in California. 

The astronomers realized right away that the event might be a Luminous Fast Blue Optical Transient (LFBOT), a rare and poorly-understood type of visual event associated with the destruction of stars. Within a day, the team obtained observations from the Liverpool Telescope in the Canary Islands and NASA's Swift satellite in space and confirmed this object had the expected properties of an LFBOT: it was very blue and it was producing X-rays. 

The phenomenon was confirmed when co-authors R. Michael Rich at UCLA and Yu-Jing Qin at Caltech provided a distance measurement to confirm that it was emitting far more energy than a normal supernova. This observation and other observations the team collected of the transient such as its extremely high temperature, led the team to conclude that they were seeing a star being torn apart and it was swallowed by a black hole.

“Even though we suspected what it was, it was still extraordinary,” added Perley. “This was many times more energetic than any similar event and more than any known explosion powered by the collapse of a star.

“Not only do these events help us identify black holes, they provide a new way to identify where black holes occur and how they form and grow, and the physics of how this happens,” Perley added.

Powerful wind of gas

Further investigations into AT2024wpp reveal it has produced a powerful shock-wave that propagated outward at one fifth the speed of light into dense surrounding gas - before suddenly "fizzling out" after about half a year.

As material in the disk spirals towards the centre, it heats up to extreme temperatures and releases both X-ray radiation and a powerful "wind" of gas that crashes into material that was shed from the star prior to its final demise, producing the luminous blue optical and ultraviolet data in the first few days as well as the radio and millimetre data detected.  The shock "fizzles" once it reaches the edge of the bubble left by the gas previously shed by the doomed star.

One mystery remains, however.  Observations from Keck Observatory, Magellan Observatory, and the Very Large Telescope revealed that while the event was devoid of recognizable chemical signatures in the first month of the initial explosion, weak signatures of hydrogen and helium gas emerged later on, as the event was fading away.  Unexpectedly, the helium was moving along the line of sight at more than 6,000 kilometres per second, suggesting a densely bound structure had survived the blast and was now moving rapidly towards us. 

The team speculates that this could originate from a "stream" of material released by the core of the star as it was torn apart by the immense gravity of the black hole.  More speculatively, it could even originate from a third member of the system as it is blasted by the fast wind of particles and X-ray radiation from the accreting black hole.