Black Holes Might Be Able To Briefly Reignite Dead Stars

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A new theory has suggested it might be possible for certain black holes to reignite dead stars – at least for a couple of seconds.

Led by Dr Chris Fragile from the College of Charleston in South Carolina, the study looked at how intermediate mass black holes (IMBHs) interact with certain objects like white dwarfs – dead stars that are no longer undergoing nuclear fusion.

The findings – to be published in The Astrophysical Journal – showed that if a white dwarf passed inside the tidal radius of an IMBH with 1,000 to 10,000 times the mass of the Sun, it could briefly reignite nuclear fusion in the star for a few seconds.

Known as a tidal disruption event (TDE), this process would cause the white dwarf to become both stretched and compressed in opposite directions. TDEs can produce huge bursts of electromagnetism that we can see on Earth, and possibly some gravitational wave signals too. It can also change the white dwarf itself.

“The nuclear burning that takes place during the tidal disruption of a white dwarf star causes significant changes to its chemical composition, converting the mostly helium, carbon, and oxygen of a typical white dwarf into elements closer to iron on the periodic table,” a statement from the College of Charleston read.

Here's a computer simulation of a white dwarf passing near a black hole. College of Charleston/Chris Fragile

Using computer simulations, Dr Fragile found that nuclear burning in this way was a common occurrence in these events. The likelihood of it happening, and the elements that are produced, depends on how close the white dwarf gets to the black hole. Distant approaches produce more calcium, whereas closer ones produce more iron.

These events are also useful in that they could help us find more IMBHs, which have been tough to find so far compared to smaller stellar mass or larger supermassive black holes. Spotting the flash of TDEs could help us get a better handle on how many IMBHs there are out there.

“It is important to know how many intermediate mass black holes exist, as this will help answer the question of where supermassive black holes come from,” Dr Fragile said in the statement. “Finding intermediate mass black holes through tidal disruption events would be a tremendous advancement.”

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