All black holes They are the fruit of a very violent activity. However, there are some for which the known processes are insufficient. Now, an international team of scientists has discovered how the most massive black holes in the Universe form. It is a process so violent that it needs a huge star cluster to support it.
Two groups of black holes. This team of scientists has analyzed the LIGO–Virgo–KAGRA Gravitational Wave Transient Catalog (GWTC4), which includes 153 detections of black hole mergers through gravitational waves. By analyzing all the available data focusing on the spin of black holes, they have seen that all of them can be divided into two large groups. On the one hand, black holes of lower mass, which arose from an ordinary stellar collapse. On the other hand, very massive black holes, arising from secondary mergers in the environment of dense star clusters.
Okay, now that you understand. Generally, black holes are formed when a very massive star that has already run out of fuel collapses. This gives rise to an explosion in which the outer layers of the star are expelled, leaving only a very dense core. It is so dense that it generates a great gravitational pull and nothing can escape from it. On the other hand, there are such massive holes that do not fit with this process. They are believed to be second generation black holes. That is, two black holes they merge and then the result merges with another black hole, becoming much more immense. That would be the second group that has been detected in the GWTC4 catalog.
Something doesn’t add up. This black hole merger process is so violent that, as soon as the first merger occurs, the result would fly away like a rocket For it to stay in place and merge with a third black hole, something is needed to retain it. These scientists have discovered that these are densely populated star clusters. There are so many stars in them that the gravitational attraction of all of them keeps the black hole still in place.
And what does spin have to do with it? Spin is a parameter that refers to the spin of black holes. When formed in the conventional way, the spin is predictable and perfectly aligned with the star that gave rise to the black hole. On the other hand, when they are formed by a process as violent as these consecutive fusions, the spin takes a random direction, but a value predictable from the sum of the spins of the rest of the black holes. These scientists, therefore, saw that all the data coincided with that hypothesis: consecutive mergers in the environment of a very populated star cluster.
A forbidden zone. On the other hand, these scientists found a forbidden strip of stellar size in which black holes could not form. There are small or huge ones, but not medium ones. Although this is something that was intuited, the complete set of data they have obtained gives a twist to what is known about the formation of black holes.
Relationship with nuclear physics. As explained by these scientists, this detected mass limit seems to be related to a series of nuclear reactions that take place inside stars. Stellar nuclear reactions are nuclear fusion. Humans have learned to control nuclear fission, but it poses risks that would be solved if we also mastered nuclear fusion. Until now It is being a complicated challengebut perhaps these new findings, obtained thanks to gravitational wave analysis, could shed a little more light on this research. Everything adds up.
Image | NASA, ESA, STScI and A. Sarajedini (University of Florida)/NASA, ESA, CSA, Ralf Crawford (STScI)
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