Giant black holes at the heart of galaxies like our Milky Way are known to occasionally feast on nearby stars. This dramatic event, called a tidal disruption event, sees the star get spaghettified and torn apart as it plunges towards the black hole. The resulting spectacle has puzzled scientists for decades, as observations revealed a less X-ray bright event than theoretical predictions suggested.
American astronomer Jack G. Hills and British astronomer Martin Rees first theorized about tidal disruption events in the 1970s and 80s. Rees predicted that half the star’s debris would remain bound to the black hole, forming a hot, luminous accretion disc. This disc, according to the theory, should radiate copious amounts of X-rays. However, most of the over 100 candidate tidal disruption events observed to date have surprisingly exhibited a visible light glow, not X-rays.
The observed temperature of the debris is a mere 10,000 degrees Celsius, similar to the surface of a moderately warm star, not the millions of degrees expected from hot gas around a supermassive black hole. Adding to the mystery, the glowing material around the black hole is several times larger than our Solar System and expanding rapidly away from the black hole at a few percent of the speed of light.
Astrophysicists have speculated that the black hole must be somehow smothered by material during the disruption to explain the lack of X-ray emissions, but no one could demonstrate how this actually occurs. This is where new simulations come into play.
Researchers have created the most detailed simulations to date, revealing the messy eating habits of black holes. They show that as the star gets spaghettified and its material is stretched into a long, thin strand, only 1% of the shredded star is actually swallowed by the black hole. The rest is blown away in a cosmic ‘burp’.
These simulations, which took over a year to run on one of the most powerful supercomputers in Australia, track the event from the initial plunge of the star to the subsequent ‘burp.’ They provide a visual representation of the spaghettification process, the debris falling back onto the black hole, and the powerful outflows generated by the black hole.
The simulations reveal that the 1% of material that does fall into the black hole generates so much heat that it powers an extremely powerful and nearly spherical outflow. This outflow effectively smothers the black hole, preventing it from swallowing more material.
These findings explain the observed characteristics of tidal disruption events, including their surprisingly low X-ray brightness and the large size of the glowing material. They also provide new insights into the evolution of black holes and their role in the growth and development of galaxies. These groundbreaking simulations offer a clearer picture of the chaotic and intricate processes at work in the universe.
