There may be an invisible universe of stars, nebulae and galaxies made up entirely of black matter. And astronomers now know how to find it.
Simply put, dark matter is a mystery. Astronomers have many independent lines of evidence that all point to the existence of some form of matter in the universe that is effectively invisible. It does not interact with light. But it has the influence of gravity on normal matter. Dark matter keeps galaxies stuck together despite their high spin rates, keeps cluster gas together despite its high temperature, bends the path of background light throughout the universe, and more. shapes the largest structure of the universe.
Despite evidence of its existence, the identities of dark matter particles remain unknown. For decades, cosmologists believed that there was only one type of dark matter particle, a species that dominated the universe. But recently they began to wonder if dark matter could be as rich and diverse as the normal universe. For example, some theories of high-energy physics predict the existence of a twin, or mirror, of every normal matter particle living in the dark sector. In this vision of the universe, there are dark electrons, dark quarks, dark neutrinos, etc., all interacting with each other through their own set of fundamental forces, completely alien. of the forces we know.
This mirror universe is everywhere, but completely invisible to us. So how do we test this idea? This is exactly the question asked by a group of astronomers in a paper, which has not yet been peer-reviewed, published on November 29 in the preprint database. arXiv. They found that, surprisingly, the mirror stars can reflect themselves, and they look very different than anything we have ever found in the universe.
Related: Dark matter may have its own ‘invisible’ periodic table of elements
Mirror stars form as different species of dark matter interact, lose energy, and clump together. This occurs in a process similar to the formation of ordinary stars, where hydrogen and helium rapidly collapse, release energy by emitting photons, and become dense enough to form stars. These mirror stars, however, interact through their own natural forces, and emit radiation – even if it is through the emission of dark photonswhich we cannot see.
There could be millions, even trillions of these dark stars floating around Milky Way galaxy alone, because dark matter makes up about 80% of the mass of each galaxy.
But importantly, as the authors realized, these mirror stars are still there gravity. That’s how we know dark matter exists in the first place. And any large, relatively compact object, whether a regular star or a mirror star, will attract matter around it. So these mirror stars pull in gas and dust floating in the interstellar medium.
That regular stuff connects itself to what the authors call “nuggets.” As the nuggets collapse they heat up and emit radiation. That radiation looks like it’s coming from a normal star, but not a type of star known to astronomers. Instead the nuggets will be very red, because they do not have the high temperatures of their normal stellar siblings, and very dark, because the nuggets are not very large.
But there are other small, dark objects in the universe, such as white dwarfs and planetary nebulae. The authors discovered that they could distinguish these nuggets from white dwarfs based on the wavelengths of electromagnetic radiation they emit. If we see what looks like a dim white dwarf but it has a wrong spectrum, it could be a small normal object sitting in the heart of a mirror star. Also, these nuggets emit light at wavelengths not seen in typical planetary nebulae.
While the idea of a mirror universe is highly hypothetical, it is a realtestable, scientific idea, the study shows. If mirror stars are out there, there might be nuggets in their hearts, and with sensitive and large enough surveys we might just find them.
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