There may be an invisible universe of stars, nebulae, and galaxies made entirely of dark matter. Astronomers now know how to look for it.
In short, dark matter is a mystery. Astronomers have dozens of independent pieces of evidence, all of which point to the presence of some kind of invisible substance in the universe. It does not interact with light. But it does have a gravitational effect on normal matter.Dark matter keeps galaxies glued together despite their high spin rates; it keeps star cluster gas cohesive despite its high temperatures; it bends the paths of background light throughout the universe, even Shaping the largest structures in the universe.
Despite evidence for its existence, the identity of dark matter particles remains unknown. For decades, cosmologists have believed that there is only one dark matter particle, a single species that dominates the universe. But recently they have begun to wonder whether dark matter is as abundant and diverse as the normal universe. For example, some high-energy physics theories predict that every particle of normal matter living in the dark zone has a twin, or mirror. In this vision of the universe, there would be dark electrons, dark quarks, dark neutrinos, etc., all interacting through their own set of fundamental forces, completely different from the forces we know.
This mirror universe is everywhere but completely invisible to us. So how do we test this idea?That’s exactly the question a team of astronomers asked in a paper published Nov. 29 on a preprint repository that has not yet been peer-reviewed arXiv. Surprisingly, they found that mirror stars may make themselves visible, and they look very different from any other stars we find in the universe.
related: Dark matter may have its own “invisible” periodic table of elements
Mirror stars form when different kinds of dark matter interact, lose energy and come together. This would unfold in a process similar to ordinary star formation, in which hydrogen and helium collapse under gravity, release energy by emitting photons, and become dense enough to form stars.However, these mirror stars interact with each other through their own natural forces and emit radiation – albeit through the release of dark photonwhich is invisible to us.
There could be millions or even trillions of dark stars floating throughout the universe Milky Way Consider that dark matter makes up about 80% of the mass of every galaxy, just for galaxies.
But crucially, as the authors realized, these mirror stars still have gravity. This is how we first learned that dark matter exists. Any massive, relatively dense object, whether a regular star or a mirror star, will attract surrounding matter through gravity. As a result, these mirror stars attract gas and dust floating in the interstellar medium.
This regular substance itself aggregates into what the authors call “gold nuggets.” As gold nuggets collapse, they heat up and emit radiation. The radiation looks like it’s coming from an ordinary star, but it’s not the type of star astronomers have identified. Instead, nuggets will be very red because they don’t have the high temperatures of their normal stellar siblings, and very dark because the nuggets aren’t very big.
But there are other small, faint objects in the universe, such as white dwarfs and planetary nebula. The authors found that they could distinguish these nuggets from white dwarfs based on the wavelength of the electromagnetic radiation they emitted. If we see something that looks like a faint white dwarf but with the wrong spectrum, it’s probably just a normal lump of matter at the center of a mirror star. In addition, these nuggets emit light at wavelengths not found in typical planetary nebulae.
Research shows that while the idea of a mirror universe is very hypothetical, it is a truly testable scientific idea. If mirror stars do exist, they may have nuggets in their hearts, and with a sensitive and large enough survey, we might be able to find them.
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