White holes
Black holes die in a violent transformation, sending all their matter back into space again and becoming white holes, according to a new theory that is to be tested, perhaps changing our idea of the universe for good.
Large swirling gas clouds and stars are sucked into the black hole, to a place where gravity is so intense that not even light can escape. But eventually the feasting stops: the black hole cannot swallow anything more because all that matter cannot be further compressed. The hole ‘reverses’ into a white hole that ejects all its matter into space with violent force. A white hole is the opposite of a black hole. Where a black hole swallows matter which cannot escape again, nothing can enter a white hole because of the enormous pressure on the matter that comes roaring back into space.
That is the sensational theory of white holes, an idea now to be tested by the new CHIME radio telescope in Canada, which began scientific operations in 2018. With CHIME, astronomers can analyse thousands of radio wave flashes that could come from white holes. And if the holes do exist, it will turn astronomy upside down.
Spacetime is made of rings
Black holes were introduced with Einstein’s general relativity theory, which describes gravity as curved space: masses bend time and space around them, and thereby attract other masses. The bigger the masses, the bigger the bending. Black holes are so massive that they swallow everything around them, and they have been proven to exist via astronomical observations.
White holes have never been directly observed, but they exist in quantum ring theory. The theory tries to unite Einstein’s general relativity theory with quantum mechanics, which describes the tiniest building blocks of atoms. According to quantum mechanics, space is the same everywhere, but according to relativity theory, space is variable, because large masses such as black holes change the curvature of space.
Quantum ring theory explains the conflict by describing how spacetime can be divided, just like the atoms of quantum mechanics, into its smallest possible components, which are rings. The rings are linked, a little like chain-mail armour, and they make up spacetime. If we had the ultimate super-microscope, we would be able to see the rings of the armour. According to the theory, nothing in the universe can ever be smaller than such a ring.
According to the classic theory of black holes, their ingested matter will become ever more concentrated towards an infinitely small point, but quantum ring
CARLO ROVELLI QUANTUM PHYSICIST
A white hole is a black hole in reverse: inside it, matter can only travel outwards.”
theory clearly implies that the limit on size will be that of a spacetime ring. When the volume reaches this limit, an intense outward pressure will switch the black hole to a white one, ejecting all its compressed matter back into space.
Violent conversions flash
During the past decade, astronomers have identified more than 60 mysterious radio wave flashes. The flashes come from sources that are relatively small – down to 10km in diameter – and yet they emit more energy in one micro-second than the Sun radiates over decades.
The life-span of a black hole is long, but the observed flashes might be evidence of white-hole conversions of small black holes that formed right after the Big Bang. These might be reaching their ring-size limit in the present and, according to the theory, when this happens, they emit radio flashes. So scientists believe that the 60+ radio flashes observed might come from the universe’s oldest black holes becoming white holes.
The wavelengths of radio flashes could reveal if the flashes are from white holes or other known phenomena. A small black hole that formed shortly after the Big Bang will emit radiation with short wavelengths when it is converted into a white hole. But at the same time these small black holes will be very far away, because they have existed since the beginning of the universe, which is constantly expanding. The original short wavelengths would therefore be stretched considerably as they reach Earth.
Larger black holes from the Big Bang live longer than the smallest ones, and when they become white, they will emit radio waves with longer wavelengths than the small black holes. But the wavelengths will not be stretched so much on the way to Earth, because the black holes are closer to us when they make the switch to white holes. Carlo Rovelli, one of the founding fathers of the quantum ring theory, believes that wavelengths from remote and close white holes will be almost identical, something unknown from other radio sources in space, where wavelength always increases with distance.
Did a white hole give birth to our universe?
The Canadian CHIME radio telescope began scientific operations in September 2018. CHIME detects radio waves by means of four 100m-long pipe-shaped antennas cut in half. The antennas cover 200 square degrees of the sky – a thousand times larger in area than a full moon and a wider view than any other radio telescope, enabling astronomers to capture thousands of radio flashes and compare their wavelengths and distances. With this data scientists can test the theory of radio flashes being triggered as a black hole turns white.
If scientists find white holes, we must reconsider how everything began. According to classic cosmology, the universe originated in an explosion – the Big Bang. But according to some scientists, the universe is born and dies over and over again. According to that theory, a newborn universe expands for billions of years, after which gravity takes over, compressing everything into a supermassive black hole. If quantum ring theory holds true, the black hole becomes a white hole, ejecting all the matter again and giving birth to a new universe. The discovery of white holes might therefore not only turn our knowledge about black holes upside down, but could also support the theory of a cyclical universe.