By Paul M. Sutter, Universe Today
A team of astronomers has claimed that observations of a sunlike star orbiting a small black hole may actually be an indication of something even more exotic – the presence of a star boson, a star composed entirely of dark matter.
The Gaia survey, led by the European Space Agency, has provided detailed maps of more than a billion stars in the Milky Way. While nearly all of these stars behaved as expected, there were some surprises. For example, one star in particular has been seen orbiting a dark companion.
The star itself was fairly typical, weighing in at 0.93 solar masses And with roughly the same chemical abundance as our sun. However, his companion did not emit any radiation at all. Most astronomers suspect that it is a black hole, which can easily explain the observational result.
However, in research recently published on arXiv Preprint server A team of astronomers notes that this particular setup is very unusual. Black holes are formed from the death of very massive stars, and it is unlikely that a star like our Sun could form as part of a binary pair with such a massive star. The authors say the scenario requires so much fine-tuning that we should be open to looking at other possibilities.
Perhaps the most exotic possibility is that the dark companion is not a black hole but a boson star. Boson stars are the result of a hypothetical form of dark matter. Dark matter itself makes up more than 80% of the total mass of every galaxy and is made up of a type of particle that is still a long way from modern physics. In some dark matter theories, dark matter is made up of bosons, which are a type of particle like photons and gluons — particles that typically carry forces of nature. But dark matter bosons would be different, and would instead populate most of the universe.
But because of their nature, boson dark matter particles can easily pile up on themselves, forming dense, compact bodies. These objects will emit no radiation at all and will appear to outside observers as if they are behaving black holes.
While it is unlikely that this observation revealed the existence of a star boson, the idea is worth considering for two reasons. First, the star is definitely orbiting something small, dense, and compact. This provides a natural testing ground for our understanding of gravity as presented by Einstein’s general theory of relativity. Finding any kind of discrepancy between theoretical predictions and observational results would be a landmark discovery.
Second, we can use this as a Case Study in the nature of boson stars. We can further investigate the properties of these alien and hypothetical objects, and use this scenario to test those ideas. While it is unlikely that these tests will come in favor of existence boson stars, the more we learn about them dark mattereven if it’s just a slow process of weeding out interesting ideas, the better.
Alexander M. Pompeo et al., A sun-like star orbiting a star boson, arXiv (2023). DOI: 10.48550/arxiv.2304.09140
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