The “Sci-Fi Star” – Is there a dark universe origin for gravitational waves?

boson star

Scientists working at the frontier of particle physics propose the existence of a theoretically ultralight exotic boson with a mass billions of times less than that of the electron. They are looking for a “darker” origin of ripples in spacetime, while proving the existence of a dark matter particle. Theories about the origin of dark matter in the universe – one of the biggest questions in science – range from suggesting it could be older than the Big Bang to the existence of galaxy-sized particles. .

Beyond the standard model

The question of which particles make up dark matter – “dark” in the sense that it does not emit radiation or interact with virtually nothing physically except by its gravitational attraction – is crucial for the physics of planets. modern particles. Observations indicate that dark matter exists, but apparently something other than the Standard Model particles constitutes it.

In September 2020, LVCthe joint body of the LIGO Science Collaboration and the Virgo Collaboration, announced the detection of the gravitational wave signal GW190521 of the merger of two stellar-mass black holes weighing 85 and 66 solar masses. The end product of the merger was an intermediate-mass black hole with 142 solar masses, and the remaining 9 solar masses were emitted as energy in the form of gravitational waves. The discovery was of critical importance because these intermediate-mass black holes have long been considered the missing link between the stellar-mass black holes that form from collapsing stars and the supermassive black holes that lurk behind the scenes. center of almost all galaxies.

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Despite its significance, the observation of GW190521 poses a huge challenge to current understanding of stellar evolution, as one of the merged black holes is of a “forbidden” size. Specifically, standard models of stellar evolution cannot form black holes with 85 times the mass of the sun.

The Boson Star Alternative

The alternative explanation says Nicolas Sanchis-Gual, a postdoctoral researcher at the University of Aveiro and the Instituto Superior Técnico (University of Lisbon), opens a new direction for the study”: a “no return” surface or event horizon. When they collide, they form a bosonic star that can become unstable, eventually collapse into a black hole, and produce a signal consistent with what LVC observed last year. Unlike ordinary stars, which are made of what we commonly call matter, boson stars are made of ultralight bosons. These bosons are one of the most attractive candidates for making up the dark matter forming about 27% of the Universe.

Ultra-light dark matter?

A new discovery involves the first sighting of boson stars, along with their building block, a new particle known as the ultralight boson that has been proposed as a constituent of what we call dark matter. If confirmed by subsequent analysis of GW190521 and other gravitational wave observations, the result would provide the first observational evidence for a long-sought dark matter candidate. Ultralight dark matter candidates are only a small fraction of the mass of an electron, unlike the more popular cold dark matter, which includes several candidates that are tens to hundreds of times the mass of an electron. proton.

Eliminate the “forbidden black hole”

The team compared the GW190521 signal to computer simulations of bosonic star mergers and found that these actually explained the data slightly better than the analysis conducted by LVC, says the team’s co-leader. Juan Calderon Bustillo, Marie Curie Fellow at the Galician Institute of High Energy Physics: “Firstly, we would no longer talk about colliding black holes, which eliminates the problem of dealing with a forbidden black hole. Second, because boson star mergers are much weaker, we infer a much closer distance than that estimated by LVC. This leads to a much larger mass for the final black hole, of around 250 solar masses, so the fact that we have seen the formation of an intermediate-mass black hole still holds true.

Relics of the Big Bang – Dark matter is made up of primordial black holes

Although the analysis tends to favor the black hole merger hypothesis “by design”, according to the astrophysicist Toni fontat the University of Valencia and one of the co-authors, “boson star merger is actually slightly preferred by the data, although not conclusively. Although the computational framework of current star simulations stars is still quite limited and subject to major improvements, the team will further develop a more evolved model and investigate similar gravitational wave observations under the bosonic star merger hypothesis.

The discovery not only involves the first sighting of boson stars, but also of their building block, a new particle known as the ultralight boson, explains the co-author, Carlos Herdeiro from the University of Aveiro. “Such ultralight bosons have been proposed as constituents of what we call dark matter. Moreover, the team can actually measure the mass of this putative new dark matter particle, and a value of zero is rejected with great confidence.

Will gravitational waves solve one of physics’ greatest mysteries?

The Last Word -J.Antonio Font

“Inference studies on GW190521 conducted by the Collaboration LIGO VIRGO KAGRA (LVK) reported a primary black hole mass of about 85 million suns (Msun),” Antonio Font wrote in an email response to The Daily Galaxy request how the observation of GW190521 poses a challenge to current understanding of stellar evolution; and did subsequent analysis confirm the existence of the ultralight boson?

“This mass is within the pair-instability supernova mass gap,” Font explained, “a range of masses between 50 Msun and 130 Msun, where black holes are not expected to form from the gravitational collapse of a massive star at the end of its evolution. While the existence of this gap seems to be a solid theoretical result, its particular limits are known to be affected by poorly understood factors, for example the rotation of the star. star, the uncertainties about the rates of nuclear reactions or the episodes of rapid accretion at the birth of the black hole.

“However, it seems unlikely, continues Font, that the lower limit of the difference could reach a value close to 85 Msun. Accordingly, there have been a number of alternative explanations for GW190521, including hierarchical captures, highly non-quasicircular mergers, high-mass torus-blackhole systems, or even exotic proposals like hole mergers primordial blacks or collisions of hypothetical bosonics. stars, the latter being our own proposal.

“We are currently reassessing our analysis with some of the more massive observations reported in GWTC-3, finding good agreement with the ultralight boson mass value that we deduced from the GW190521 signal. While this further supports our claim of a close degeneracy between two theoretical models (black hole collisions versus bosonic star collisions), it in no way implies (much less confirms) the existence of ultralight bosons . Strong support for their existence could come from the detection of continuous gravitational waves from boson clouds around rotating black holes.

If confirmed by subsequent analysis of GW190521 and other gravitational wave observations, the result would provide the first observational evidence for a “darker” origin of ripples in spacetime and prove the existence of a dark matter particle. Event G2190521 was detected near the edge of our observable universe at a distance of 5.3 gigaparsecs (17 billion light-years). Mergers closer to black holes spanning the stellar mass/intermediate mass boundary may help confirm the nature of these elusive objects.

Maxwell Moeastrophysicist, NASA Einstein Fellow, University of Arizona via Jose Antonio Font, Chinese University of Hong Kong and Physical examination letters

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