At the moment no one has been able to observe any. But we owe our existence to the most special of all: the Big Bang of 13.8 billion years ago can be considered an event caused by a supermassive white hole.
A large mass like a planet can deform spacetime. Source: Mysid [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]
The theory of general relativity considers that spacetime can be deformed by the effect of acceleration or by the presence of massive objects. This is the same theory that predicted the existence of black holes, of which white holes would be the counterpart. Therefore, its existence is considered equally possible.
Now, to form the spatiotemporal singularity, some physical mechanism is needed. In the case of black holes, the cause is known to be the gravitational collapse of a supermassive star.
But the physical mechanism that could form a white hole singularity is not yet known. Although, of course, candidates have come up to explain their possible training, as will be seen shortly.
Differences between black holes and white holes
Many of the known black holes are the remnants of a supergiant star that has collapsed internally.
When this happens, the gravitational forces increase to the point that nothing that comes close can escape their influence, not even light.
That’s why black holes are able to swallow everything that falls into them. On the contrary, nothing could enter a white hole, everything would be rejected or repelled from it.
Is the existence of such an object possible? After all, black holes remained for a long time as a mathematical solution to Einstein’s field equations, until they were detected thanks to the gravitational and radiation effects they cause in their environment and to be photographed recently.
Instead, the white holes are still hidden from cosmologists, if they really exist.
History of your discovery
The theory of the existence of white holes was based on the work of Karl Schwarzschild (1873-1916), a German physicist and the first to find an exact solution to Albert Einstein’s relativistic field equations.
For that, he developed a model with spherical symmetry whose solutions have unique singularities, which are precisely black holes and their white counterparts.
Schwarzschild’s work wasn’t exactly popular, perhaps because it was published during World War I. We had to wait a few years for two physicists to independently pick it up in the 1960s.
In 1965, mathematicians Igor Novikov and Yuval Ne’eman analyzed Schwarzschild’s solutions, but using a different coordinate system.
At that time, the term white hole had not yet been coined. In fact, they were known as “backward cores” and were considered unstable.
However, being the counterpart of black holes, the researchers tried to find a physical object whose nature was compatible with that predicted for white holes.
Quasars and white holes
The researchers thought they found in quasars, the brightest objects in the universe. They emit an intense stream of radiation detectable by radio telescopes, just as a white hole should.
However, the energy of quasars has finally been given a more viable explanation, related to black holes at the center of galaxies. And so, the white holes were again like abstract mathematical entities.
So, even though they are known, white holes have received far less attention than black holes. This is not just because they are unstable, which questions their real existence, but because there are no reasonable assumptions about their possible origin.
Rather, black holes arise from the gravitational collapse of stars, a physical phenomenon that has been well documented.
Possible discovery of a white hole
There are researchers convinced that they finally detected a white hole in a phenomenon called GRB 060614, which occurred in 2006. This phenomenon has been proposed as the first documented appearance of a white hole.
GRB 060614 was a gamma-ray burst detected by the Neil Gehrels Swift Observatory on June 14, 2006, with peculiar properties. He challenged a previously held scientific consensus on the origins of gamma-ray bursts and black holes.
The Big Bang, which some believe to be a supermassive white hole, in turn could have been the result of a supermassive black hole at the heart of an unknown galaxy located in our parent universe.
One of the difficulties with observing a white hole is that all matter is expelled from it in a single pulse. Therefore, the white hole lacks the necessary continuity to be observed, but black holes are persistent enough to be seen.
Einstein postulates that mass, time and length are highly dependent on the speed of the reference system in which they are being measured.
Furthermore, time is considered as another variable, with the same meaning as spatial variables. Thus, spacetime is referred to as an entity in which any event and all events occur.
Matter interacts with the fabric of spacetime and modifies it. Einstein describes how this happens with a set of 10 tensor equations, known as field equations.
Some important concepts in relativity theory
The tensioners are mathematical entities that allow Us to consider the temporary variable at the same level of spatial variables. Vectors known as force, velocity and acceleration are part of this expanded set of mathematical entities.
The mathematical aspect of Einstein’s equations also involves concepts such as metrics , which is the distance in space and time that separates two infinitesimally close events.
Two points in spacetime are part of a curve called geodesic . These points are linked to a spatiotemporal distance. This representation of temporal space is observed in the following figure:
The shape of the cone is determined by the speed of light c , which is a constant in all frames of reference. All events must take place within the cones. If there are events outside of them, there is no way to know, because information must travel faster than light to be perceived.
Einstein’s field equations assume a solution with two singularities in an empty (ie, massless) region. One of these singularities is a black hole and the other is a white hole. For both, there is an event horizon, which is a spherical edge of finite radius that surrounds the singularity.
In the case of black holes, nothing, not even light, can leave this region. And in white holes, the event horizon is a barrier that nothing can pass outside. The black hole solution in vacuum is in the cone of light of the future, while the white hole solution is in the past region of the cone of light.
Solutions to Einstein’s equations that comprise a real black hole require the presence of matter, in which case the solution that contains the white hole disappears. Therefore, it is concluded that, as a mathematical solution, in the theory of matterless singular solutions, there are white holes. But this is not the case when matter is included in Einstein’s equations.
How is a white hole formed?
In 2014, theoretical physicist Carlo Rovelli and his team at the University of Aix-Marseille in France proposed that white holes can arise from the death of a black hole.
As early as the 1970s, the ultimate black hole expert, Stephen Hawking, calculated that a black hole loses mass through the emission of Hawking radiation.
Rovelli and his team’s calculations indicate that this contraction due to loss of radiation from a black hole can, in its final phase, produce a recovery that causes a white hole.
But Rovelli’s calculations also indicate that, in the case of a black hole with a mass equal to that of the Sun, the current age of the Universe would be needed approximately four times as much to form a white hole.
White holes and dark matter
A second after the Big Bang, density fluctuations in a rapidly expanding Universe could produce primordial black holes (without the need for stellar collapse).
These primordial black holes are much smaller than those of stellar origin and can evaporate to death to give way to a white hole at some point in the universe’s life.
White microscopic holes can be very large. For example, one the size of a speck of dust might have a mass greater than the Moon.
Even Rovelli’s team suggests that these microscopic white holes may explain dark matter, another of the most important cosmological mysteries.
Microscopic white holes do not emit radiation; and because they are smaller than one wavelength, they become invisible. That could be another reason that would explain why they haven’t been detected yet.