Merging forest monsters could explain the massive collision between black holes and reveal the existence of dark matter

An international team of scientists led by the Galician Institute of High Energy Physics (IGFAE) and the University of Aveiro shows that the most severe black hole collision ever observed, caused by the gravitational wave GW190521, is perhaps even more mysterious: the fusion of two forest monsters. This would be the first evidence of the existence of these hypothetical objects, which qualify for dark matter, which are believed to make up 27% of the mass in the universe.

Gravitational waves are ripples in the fabric of spacetime that travel at the speed of light. These originate from the most violent events in the universe and contain information about their sources. Since 2015, the two LIGO detectors in the US and the Virgo detector in Cascina, Italy, have detected and interpreted gravitational waves. To date, these detectors have already detected about 50 gravitational wave signals. All of these were created by collisions and mergers of black holes and neutron stars, allowing physicists to deepen their knowledge of these objects.

However, the promise of gravitational waves goes far beyond this, as they should ultimately provide us with evidence for previously unobserved and even unexpected objects, and shed light on current mysteries such as the nature of dark matter. However, the latter may have already happened.

In September 2020, the collaboration between LIGO and Virgo (LVC) announced the gravitational wave signal GW190521 to the world. According to their analysis, the signal was consistent with the collision of two massive black holes, 85 and 66 times the mass of the sun, producing a final black hole with 142 solar masses. The resulting black hole was the first of a new, previously unobserved family of black holes: medium black holes. This discovery is of paramount importance, as such black holes were the missing link between two known black hole families: black holes with a stellar mass created by the collapse of stars, and supermassive black holes that lie at the center of almost each. galaxy, including the Milky Way.

Moreover, this observation presented an enormous challenge. If what we think we know about how stars live and die is correct, the heaviest of the colliding black holes (85 solar masses) cannot be caused by the collapse of a star at the end of its life, raising a series of doubts . and possibilities about its origin.

In an article published today in Physical Review Letters, a team of scientists led by Dr. Juan Calderón Bustillo of the Galician Institute of High Energy Physics (IGFAE), the joint center of the University of Santiago de Compostela and Xunta de Galicia, and Dr. Nicolás Sanchis-Gual, a postdoctoral fellow at the University of Aveiro and the Instituto Superior Técnico (Univ. Lisboa), together with staff from the University of Valencia, Monash University and the Chinese University of Hong Kong, have proposed an alternative explanation for the origin of the signal GW190521: the collision of two exotic objects known as forest monsters, which are one of the most likely candidates to explain dark matter. In their analysis, the team was able to estimate the mass of a new particle component of these stars, an ultra-light boson with a mass billions of times smaller than electrons.

The team compared the GW190521 signal to computer simulations of boson star fusions and found that these actually explain the data slightly better than LIGO and Virgo’s analysis. The result implies that the resource would have different properties than previously stated. Dr. Calderón Bustillo says, “First, we would stop talking about colliding black holes, eliminating the problem of dealing with a ‘forbidden’ black hole. Second, because forest monster mergers are much weaker, we conclude a much closer distance. than estimated by LIGO and Virgo. This leads to a much larger mass for the last black hole, of about 250 solar masses, so the fact that we witnessed the formation of a black hole of medium mass remains true. ”

Dr. Nicolás Sanchis-Gual says: “Forest monsters are objects that are nearly as compact as black holes, but unlike them, do not have a ‘no-return’ surface. When they collide, they form a forest monster that can eventually become unstable. collapse into a black hole, producing a signal similar to what LIGO and Virgo observed. Unlike ordinary stars, which are made of what we commonly know as matter, forest monsters are made up of what we know as ultra-light bosons. These bosons are one of the most attractive candidates for forming what we know as dark matter. ”

The team found that while the analysis favors the black hole merging hypothesis, a forest monster fusion is preferred among the data, albeit in a non-conclusive way. Prof. Jose A. Font of the University of Valencia says, “Our results show that the two scenarios are almost indistinguishable from each other given the data, although the exotic forest monster hypothesis is somewhat preferable. This is very exciting considering our boson star. model is, as of now, very limited and subject to major improvements, a more developed model could provide further evidence for this scenario and also allow us to study previous observations of gravitational waves under the assumption of a boson star aggregation. ”

This result includes not only the first observation of forest monsters, but also that of their building block, a new particle known as an ultra-light boson. Prof. Carlos Herdeiro of the University of Aveiro says: “One of the most fascinating results is that we can actually measure the mass of this supposed new dark matter particle, and that a value of zero is discarded with great certainty. analysis of these and other gravitational wave observations, our result would provide the first observational evidence for a long-sought dark matter candidate. ”