Black holes exploding into 'white holes'

The collapse of a star into a black hole could be a temporary effect that leads to the formation of a 'white hole', suggests a new model based on a theory known as loop quantum gravity.

A new scientific theory suggests that when black holes reach the end of their lifespan, they explode into "white holes" and release all of their matter into space.

If true, the theory could help put to rest the debate over whether or not black holes actually destroy the matter they end up devouring.

As noted by Albert Einstein's theory of relativity, when a dying star ends up collapsing under its own weight, at some point the collapse becomes irreversible, resulting in a black hole that consumes light and anything else within its surrounding area.

Although black holes do slowly leak radiation over time, ultimately draining the black hole completely, this doesn't account for all the other matter that the dying star has consumed.

Since quantum theory does not allow for the possibility that information can be lost, though, two researchers from France's Aix-Marseille University believe they've discovered an explanation for this so-called "information paradox."

Carlo Rovelli

According to physicists Carlo Rovelli and Hal Haggard, a black hole eventually reaches a point where it cannot collapse any further and the internal pressure begins to push outwards.

This essentially turns the black hole inside out and expels everything it once consumed back into space.

Notably, the scientists believe that these white holes are created not long after the black hole's original formation, and we humans can't see it because gravity dilates time and makes the black hole's lifespan seem to last for billions or trillions of years.

Their current calculation is that it only takes a few thousandths of a second for a black hole to turn into a white hole.

Hal Haggard

Importantly, the process is very long seen from the outside, but is very short for a local observer at a small radius," the researchers wrote in a paper on the subject.

Ron Cowen, a science writer at Nature, explained further.

If the authors are correct, tiny black holes that formed during the very early history of the Universe would now be ready to pop off like firecrackers and might be detected as high-energy cosmic rays or other radiation.

In fact, they say, their work could imply that some of the dramatic flares commonly considered to be supernova explosions could in fact be the dying throes of tiny black holes that formed shortly after the Big Bang.

Although Rovelli and Haggard aren't completely dismissing the idea that black holes leak radiation, they said the trickles of energy would not be sufficient enough to deplete the dying stars of all the energy they've consumed.

Radiation may very well seep out, but their work is primarily concerned with discovering what happens inside a black hole.

Both Rovelli and Haggard admitted that their theory needs to be tested further with more comprehensive calculations.

If research confirms their ideas, however, theoretical physicist Steven Giddings of the University of California Santa Barbara says, "It would be important. Understanding how information escapes from a black hole is the key question for the quantum mechanics of black holes, and possibly for quantum gravity itself."

Theoretical physicist Stephen Hawking of the University of Cambridge, UK, has recently suggested that true event horizons would be incompatible with quantum physics.

More Information: Black hole fireworks: quantum-gravity effects outside the horizon spark black to white hole tunneling - Authors: Hal M. Haggard, Carlo Rovelli - arXiv:1407.0989

Astrophysicists propose 'Planck star' are core of black holes

This artist's concept depicts a supermassive black hole at the center of a galaxy. 

The blue colour here represents radiation pouring out from material very close to the black hole. 

The grayish structure surrounding the black hole, called a torus, is made up of gas and dust. 

Credit: NASA/JPL-Caltech

Two astrophysics, Carlo Rovelli, Centre de Physique Theorique de Luminy and Francesca Vidotto, Radboud University Nijmegen, have uploaded a paper to the preprint server arXiv in which they suggest that a structure known as a Planck star exists at the center of black holes, rather than a singularity.

Carlo Rovelli

This would suggest, they note, that black holes at some point return all the information they have pulled in, to the universe.

The current thinking regarding black holes is that they have two very simple parts, an event horizon and a singularity.

Because a probe cannot be sent inside a black hole to see what is truly going on, researchers have to rely on theories.

The singularity theory suffers from what has come to be known as the "information paradox"—black holes appear to destroy information, which would seem to violate the rules of general relativity, because they follow rules of quantum mechanics instead.

This paradox has left deep thinking physicists such as Stephen Hawking uneasy—so much so that he and others have begun offering alternatives or amendments to existing theories. In this new effort, a pair of physicists suggest the idea of a Planck star.

Francesca Vidotto

The idea of a Planck star has its origins with an argument to the Big Bang theory, this other idea holds that when the inevitable Big Crunch comes, instead of forming a singularity, something just a little more tangible will result, something on the Planck scale.

And when that happens, a bounce will occur, causing the universe to expand again, and then to collapse again and so on forever back and forth.

Rovelli and Vidotto wonder why this couldn't be the case with black holes as well—instead of a singularity at its center, there could be a Planck structure, a star, which would allow for general relativity to come back into play.

If this were the case, then a black hole could slowly over time lose mass due to Hawking Radiation, as the black hole contracted, the Planck star inside would grow bigger as information was absorbed.

Eventually, the star would meet the event horizon and the black hole would dematerialise in an instant as all the information it had ever sucked in was cast out into the universe.

This new idea by Rovelli and Vidotto will undoubtedly undergo close scrutiny in the astrophysicist community likely culminating in debate amongst those who find the idea of a Planck star an answer to the information paradox and those who find the entire idea implausible.

More information: Planck stars, arXiv:1401.6562 [gr-qc] arxiv.org/abs/1401.6562