For a long time, astronomers thought that a peculiar star system observed by the European Space Agency’s Gaia satellite was simply a case of a star orbiting a black hole. But now, two astronomers challenge that claim, finding that the evidence suggests something much stranger: possibly a never-before-seen type of star made of invisible dark matter. Their research, which has not yet been peer-reviewed, was posted on the preprint server on April 18. arXiv.
The system itself consists of a sun-like star and, well, something else. The star weighs slightly less than the sun (0.93 solar mass) and has about the same chemical abundance as our star. Its mysterious companion is much more massive: around 11 solar masses. The objects orbit each other at a distance of 1.4 astronomical units, roughly the distance that Mars orbits the sun, completing one orbit every 188 days.
What could that dark companion be? One possibility is that it is a black hole. While that would easily fit in terms of orbital observations, that hypothesis has challenges. Black holes are formed from the death of very massive stars, and for this situation to arise, a star similar to the Sun would have to form in the company of one of those monsters. While not entirely impossible, that scenario requires an extraordinary amount of adjustment for the coincidence to happen and to keep these objects in orbit around each other for millions of years. So perhaps that dark orbital companion is something much more exotic, as the researchers propose in the new study. Perhaps, they suggest, it is a group of dark matter particles.
Dark matter is an invisible form of matter that makes up the vast majority of the mass in every galaxy. We still don’t have a solid understanding of his identity. Most theoretical models assume that dark matter is evenly distributed in each galaxy, but there are models that allow it to accumulate on itself.
One of these models hypothesizes that dark matter is a new type of boson. Bosons are the particles that carry the forces of nature; for example, a photon is a boson that carries the electromagnetic force. While we know of only a limited set of bosons in the Standard Model of particle physics, there is nothing, in principle, to prevent the universe from having many more types. These types of bosons would not carry forces, but they would still drench the universe. Most importantly, they would have the ability to form large groups. Some of these groups could be the size of entire star systems, but some could be much smaller. The smallest clumps of bosonic dark matter could be as small as stars, and these hypothetical objects are given a new name: bosonic stars.
Boson stars would be completely invisible. Because dark matter does not interact with other particles or with light, we can only detect it through the gravitational influence on its surroundings, just as if a normal star orbited a bosonic star.
The researchers noted that a simple boson dark matter model could produce enough boson stars to make this result plausible in the Gaia data, and that replacing a putative black hole with a boson star could explain all the observational data. While it is unlikely that this is actually the discovery of a boson star, the authors still urged follow-up observations. Most importantly, this unique system provides us with a rare opportunity to study the behavior of strong gravity, allowing us to examine Einstein’s theory. theory of general relativity to see if it holds up. Second, if it is a bosonic star, this system is the perfect experimental setup.
source : https://arxiv.org/abs/2304.09140