“Heaviest Black Hole Collision” Detected by Gravitational Waves Might Actually Be a Boson Star Merger

An worldwide group of researchers led by the Galician Institute of High Energy Physics and the University of Aveiro, consisting of an undergraduate from the Department of Physics at The Chinese University of Hong Kong (CUHK), has actually proposed the crash of 2 unique compact items referred to as boson stars as an alternative description for the origin of the gravitational wave signal GW190521. The theoretical stars are amongst the easiest unique compact items proposed and make up well established dark matter prospects. Within this analysis, the group has the ability to approximate the mass of a brand-new particle constituent of these stars, an ultra-light boson with a mass billions of times smaller sized than that of the electron. Their analysis has actually been released in the journal Physical Review Letters on February 24, 2021.

The group is co-led by Dr. Juan Calderón Bustillo, a previous teacher from the Department of Physics at CUHK and now “La Caixa Junior Leader – Marie Curie Fellow”, at the Galician Institute of High Energy Physics, and Dr. Nicolás Sanchis-Gual, a postdoctoral scientist at the University of Aveiro and at the Instituto Superior Técnico (University of Lisbon). Other partners originated from the University of Valencia, the University of Aveiro and Monash University. Samson Hin Wai Leong, a second-year undergrad at CUHK, likewise got involved.

Gravitational waves are ripples in the material of spacetime that travel at the speed of light. Predicted in Einstein’s General Theory of Relativity, they come from the most violent occasions of the Universe, bring info about their sources. Since 2015, the innovative detectors of the Laser Interferometer Gravitational Wave Observatory (LIGO) and Virgo have actually observed around 50 gravitational wave signals come from the coalescence and merger of 2 of the most mystical entities in the Universe — great voids and neutron stars.

In September 2020, LVC, the joint body of the LIGO Scientific Collaboration and the Virgo Collaboration, revealed the detection of the gravitational wave signal GW190521. According to the LVC analysis, in which the CUHK group led by Professor Tjonnie Li, Associate Professor of the Department of Physics at CUHK was deeply included, the signal followed the crash of 2 great voids of 85 and 66 times the mass of the Sun, which produced a last 142 solar mass great void. The latter was the very first member ever discovered of a brand-new great void household — intermediate-mass great voids. According to Professor Tjonnie Li, this discovery was of critical significance since such great voids had actually been long thought about the missing out on link in between the stellar-mass great voids that form from the collapse of stars, and the supermassive great voids that conceal in the center of nearly every galaxy.

Despite its significance, the observation of GW190521 positions a massive difficulty to the present understanding of excellent advancement, since among the great voids combined has a “forbidden” size. The alternative description proposed by the group brings a brand-new instructions for the research study. Dr. Nicolás Sanchis-Gual described, “Boson stars are objects almost as compact as black holes but, unlike them, they do not have a ‘no return’ surface or event horizon. When they collide, they form a boson star that can become unstable, eventually collapsing to a black hole, and producing a signal consistent with what LVC observed last year. Unlike regular stars, which are made of what we commonly know as matter, boson stars are made up of ultra-light bosons. These bosons are one of the most appealing candidates for constituting dark matter forming around 27% of the Universe.”

The group compared the GW190521 signal to computer system simulations of boson star mergers and discovered that these in fact describe the information a little much better than the analysis carried out by LVC. The result suggests that the source would have various homes than specified previously. Dr. Juan Calderón Bustillo stated, “First, we would not be talking about colliding black holes anymore, which eliminates the issue of dealing with a forbidden black hole. Second, because boson star mergers are much weaker, we infer a much closer distance than the one estimated by LVC. This leads to a much larger mass for the final black hole, of about 250 solar masses, so the fact that we have witnessed the formation of an intermediate-mass black hole remains true.”

Professor Toni Font, from the University of Valencia and among the co-authors, described that despite the fact that the analysis tends to favour “by design” the combining great voids hypothesis, a boson star merger is in fact a little chosen by the information, although in a non-conclusive method. Despite the computational structure of the present boson star simulations being still relatively minimal and based on significant enhancements, the group will even more establish a more developed design and research study comparable gravitational wave observations under the boson star merger presumption.

According to another co-author, Professor Carlos Herdeiro from the University of Aveiro, the finding not just includes the very first observation of boson stars, however likewise that of their foundation, a brand-new particle referred to as the ultra-light boson. Such ultra-light bosons have actually been proposed as the constituents of what we understand as dark matter. Moreover, the group can in fact determine the mass of this putative brand-new dark matter particle and a worth of no is disposed of with high self-confidence. If it is verified by the subsequent analysis of GW190521 and other gravitational wave observations, the outcome would offer the very first observational proof for a long looked for dark matter prospect.

Samson Hin Wai Leong, a trainee who signed up with the summertime undergraduate research study internship program of CUHK included, “I worked with Professor Calderón Bustillo on the design of the software of this project, which successfully speeded up the calculations of the study, and eventually we were able to release our results immediately after LVC published their analysis. It is thrilling to work at the frontier of physics with the multicultural team and think about seeking a ‘darker’ origin of the ripples in spacetime, at the same time proving the existence of a dark matter particle.”

Reference: “GW190521 as a Merger of Proca Stars: A Potential New Vector Boson of 8.7×10⁻¹³  eV” by Juan Calderón Bustillo, Nicolas Sanchis-Gual, Alejandro Torres-Forné, José A. Font, Avi Vajpeyi, Rory Smith, Carlos Herdeiro, Eugen Radu and Samson H. W. Leong, 24 February 2021, Physical Review Letters.
DOI: 10.1103/PhysRevLett.126.081101