Astronomers have discovered black holes don't just 'eat' stars — they 'burp' them back up as 'stellar ghosts'

When a star approaches a black hole, it's usually torn apart by the sheer strength of tidal forces and, normally, its remains are then "eaten up" by the respective black hole.

However, astrophysicists have now discovered in a study published on the Cornell University Library website that, equally, a black hole can also "revive" a star under a very specific set of conditions.

The first prerequisite is that the star has to be a white dwarf — in other words, it has to be a relatively small star, in its final stages of life.

The second condition to be met is that the black hole has to be just the right size — if it's too large or too small, the black hole will either completely engulf the white dwarf or completely ignore it.

At just the right-size, a black hole can 'burp' a dead star back to life

When a white dwarf approaches a black hole, it's simultaneously expanded and compressed by the forces surrounding it.

This phenomenon is called a "tidal disruption event".

If a white dwarf passes a black hole of just the right size, the black hole can "bring it back to life".

During contraction, the core of the white dwarf — in which nuclear fusion will usually have come to a standstill during its final life phase — will come back to life once again, even if only for an extremely short time.

Read more: The fastest-growing black hole in the universe eats a sun every 48 hours — and astronomers have found it

This spectacular phenomenon has only been observed using simulated models so far, the main reason being that there hasn't been a single perfectly sized black hole found in the universe.

Researchers have only been able to find black holes either with a mass of roughly 100 suns, or with a mass of over 100,000 suns — but using the theory developed by these scientists, there should also be appropriately sized black holes somewhere in between that we can one day find.

Scientists are starting to further unravel the secrets of black holes

"Finding intermediate mass black holes through tidal disruption events would be a tremendous advancement," said Chris Fragile, an astrophysicist from the College of Charleston, in a press release.

The model has shown that the event produces gravitational waves that are not yet measurable because we don't yet have the necessary equipment — but that will provide clues for black hole locations in the future.

"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," he said.

If the researchers find a way to locate them, there may be more secrets about black holes we can uncover in the near future.