We Finally Know What Happens When A Black Hole Devours A Star

Artist's impression of a star being destroyed by a black hole. NASA/JPL-Caltech

Supermassive black holes are known for their incredible voracity, ripping stars apart when they wander too close and gobbling them up, but in reality, we have only observed such events a couple of dozen times. These observed events have varied greatly and now scientists have created a model to try to explain them all.

According to astrophysicists from Denmark and California, the viewing angle of the observer is key to what we actually see. Due to the complex environment around supermassive black holes, such as a large ring of gas and dust, we might see different parts of stars being torn apart – technically known as a tidal disruption event. Their work is published in the Astrophysical Journal Letters.

"It is like there is a veil that covers part of a beast," co-author Professor Enrico Ramirez-Ruiz explained in a statement. "From some angles, we see an exposed beast, but from other angles, we see a covered beast. The beast is the same, but our perceptions are different.

"Only in the last decade or so have we been able to distinguish TDEs from other galactic phenomena, and the new model will provide us with the basic framework for understanding these rare events." 

Supermassive black holes are found in all galaxies and are mostly quiescent, not feeding or doing anything else. It’s when they get a steady supply of materials that things get interesting. Then they start to emit intense radiation and produce things like relativistic jets. Tidal disruption events are part of this process but they are rarer. Usually, there’s one every 10,000 years in a typical galaxy. A star approaching a black hole will be ripped apart by the intense gravity of the object, and its plasma will swirl around the black hole being heated to very high temperatures.

"It is interesting to see how materials get their way into the black hole under such extreme conditions," said first author Jane Lixin Dai, an assistant professor at the University of Copenhagen. "As the black hole is eating the stellar gas, a vast amount of radiation is emitted. The radiation is what we can observe, and using it we can understand the physics and calculate the black hole properties. This makes it extremely interesting to go hunting for tidal disruption events."

The model will be tested in the next few years. Several survey projects are in the works and researchers expect to observe hundreds to thousands of these events taking place in the sky.

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