For the most violent collisions in the cosmos, scientists have discovered a new speed limit.
The “maximum possible recoil velocity” for merging black holes is estimated to be greater than 63 million mph (102 million km/h), or around one-tenth the speed of light, according to recent study. According to a study published in the journal Physical Review Letters, this peak occurs when the collision conditions are at the point when the two black holes are either merging together or scattering apart as they approach one another
The researchers next intend to use Einstein’s general relativity equations to quantitatively demonstrate that this velocity cannot be exceeded, raising possible consequences for the fundamental rules of physics.
According to research co-author Carlos Lousto, a professor of mathematics and statistics at the Rochester Institute of Technology (RIT) in New York, “We are just scratching the surface of something that could be a more universal description.” According to Lousto, there may be a bigger collection of physical principles that apply to everything, “from the smallest to the largest objects in the universe,” that include this recently discovered speed restriction.
Quakes in the fabric of space-time
Black holes that are near to one another will either merge or deviate from their shared center of mass before breaking apart. The distance between the black holes at their closest approach determines whether they will fly apart or spiral into one another.
Lousto and James Healy, a research associate in the RIT School of Mathematics and Statistics, used supercomputers to run numerical simulations to determine the highest conceivable recoil speed of black holes traveling apart. These simulations iterated through the general relativity equations defining the evolution of two interacting black holes. Lousto noted that while numerical techniques for resolving these equations were developed more than 50 years ago, it wasn’t until 2005 — just 10 years before gravitational waves themselves were discovered by the Laser Interferometer Gravitational-Wave Observatory (LIGO) — that numerical techniques for predicting the size of gravitational waves from such collisions were created.
Since then, LIGO has seen almost 100 collisions between black holes. Numerical relativity statistics were compared to the data from one of these collisions to reveal a “eccentric,” or elliptical, black hole track. According to Lousto, scientists previously believed that black holes in close proximity would spiral toward one another in nearly circular orbits. The discovery of elliptical orbits increased the variety of collision events that could occur and led researchers to search for the most extreme collision possibilities. Lousto stated, “What we wanted to do was kind of test the bounds of these encounters.
Lousto and Healy examined how changing four factors—the initial momenta of the black holes, their distance at their closest approach, the direction and magnitude of any rotation the black hole might have around its own axis—affected the outcome of gravitational engagement between two black holes.
The researchers discovered a peak in the potential recoil velocities for black holes with opposing spins grazing past one another by running 1,381 simulations, each of which took two to three weeks. Black holes emit gravitational radiation in all directions, but because of the distortion caused by the opposing spins, the recoil velocity is increased.
Imre Bartos, an associate professor in the physics department at the University of Florida, told Live Science via email that the recoil of black holes after they merge is a crucial component of their interaction. (Bartos was not engaged in the new study). Large recoil kicks from this interaction could completely expel a residual black hole from an area of the universe where there is a high density of black holes.
It will be intriguing to see whether nature exceeds this in any circumstances that would indicate variations from our understanding of how black holes operate, Bartos continued.
New fundamental physics
Lousto claims that there is some room for variation in the orbits of the black holes at the “tipping point” that decides whether two colliding black holes would merge or recoil. As a result, Lousto compares this interaction to a smooth phase transition, similar to the second-order phase transitions of magnetism and superconductivity, as opposed to the explosive first-order phase transitions of, for instance, heated water, where a finite amount of latent heat is absorbed before it all boils. Further high-resolution simulations are required to clearly identify these scaling variables, but the researchers caught a glimmer of something that might resemble them.
However, Lousto noted that these characteristics of the findings raise the prospect of “an overarching principle” that holds true at all scales, from atoms to colliding black holes.
Additionally, while unifying the two fundamental pillars of physics—quantum theory for the four fundamental forces and general relativity for gravity—remains elusive, descriptions of black holes are closely related to various ideas that have weakened the boundaries between the two.
Lousto remarked, “This is far from being a thorough evidence. However, one line merits additional study so that perhaps we or someone else can use it for something.
