Astronomers have long thought that a strange star system observed by the European Space Agency’s Gaia satellite was a simple case of a star orbiting a black hole.
But now, two astronomers are challenging that claim, finding that the evidence suggests something far more unknown: Possibly, a never-before-seen type of star made of invisible dark matter. Their research, which has not yet been peer-reviewed, was published April 18 on the preprint server arXiv.
The system itself consists of a sunlike star and, well, something else. The mass of the star is slightly less than the sun (0.93 solar mass) and has about the same chemical mass as the sun. Its mysterious companion is much larger — about 11 solar masses. The objects orbit each other at a distance of 1.4 astronomical units, about the distance at which Mars orbits the sun, making a complete orbit every 188 days.
Related: What is dark matter?
What could that dark companion be? One possibility is that it is a black hole. While that fits the bill easily in terms of orbital observations, that hypothesis has challenges. Black holes form from the death of massive stars, and for this situation to arise, a sun-like star must have formed along with one of those monsters. While not outright impossible, that scenario would require an extraordinary amount of fine-tuning to make the match and keep these objects in orbit with each other for millions of years.
So perhaps the dark orbital companion is something more exotic, as the researchers in the new study suggest. Perhaps, they suggest, it is a cluster of dark matter particles.
Dark matter is an invisible form of matter that makes up most of the mass of every single galaxy. We still don’t have a firm understanding of its identity. Most theoretical models assume that dark matter is evenly distributed throughout each galaxy, but there are models that allow it to cluster on itself.
One of these models suggests 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. Although we know that the set of bosons in the Standard Model of particle physics is limited, there is nothing, in principle, that prevents the universe from having many more types.
These types of bosons do not carry forces, but they still permeate the universe. Most importantly, they will have the ability to form large clusters. Some of these clusters may be as large as entire star systems, but some may be smaller. The smallest clusters of bosonic dark matter can be as small as stars, and these hypothetical objects are getting a new name: boson stars.
Boson stars will be completely invisible. Because dark matter does not interact with other particles or with light, we can only detect them through the gravitational influence around them — just as if a regular star were orbiting a boson star.
The researchers pointed out that a simple boson dark matter model could produce enough boson stars to make the result in the Gaia data possible, and that replacing a putative black hole with a boson star could explain all the data. of observation.
Although this is unlikely to be the actual discovery of a boson star, the authors still encourage follow-up observations. Most importantly, this unique system gives us a rare opportunity to study the behavior of strong gravity, allowing us to examine Einstein’s theory of general relativity to see if it lasts. Second, if it is a boson star, this system is the perfect experimental setup. We can play with our boson star models and see how well they explain the orbital dynamics of this system and use that information to glimpse the dark corners of the universe.
Originally published on LiveScience.com.