Dark matter may occupy a mirror universe, parallel to our own â and if so, we may be able to spot a strange kind of mirror star.
To explain dark matter, the as-yet undetected form of matter that makes up some 85 per cent of the total mass of the universe, some scientists have proposed the idea of a mirror universe. This universe would be composed of atomic dark matter, containing dark matter versions of our atoms and particles such as dark protons and dark electrons.
âUnder this theory, you would get stars that are like the normal stars we see, like our sun, but they would be made of dark matter,â says at the University of Toronto in Canada. âThey would emit dark photons.â
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Mirror stars would grow up to 10 times the size of our sun and also have nuclear fusion taking place at their cores, except with dark hydrogen fusing into dark helium. Normally, such stars would be invisible to us, as they wouldnât emit visible light or interact with matter in our universe. However, Armstrong and her colleagues have proposed a way such stars might be seen, if they contain clumps of regular matter within them.
As a mirror star drifts through a galaxy, its gravitational pull might draw in normal matter in the form of gas from nebulae. âThat gas begins to heat and emit light,â says Armstrong. Within the invisible mirror star, a ânuggetâ of visible matter might look quite similar to a white dwarf, the remnant cores of sun-like stars left behind at the end of their lives. But it would emit a very noticeable signal of X-rays and visible light, say the researchers. âSo thatâs how you can tell them apart,â says Armstrong.
at the University of Maryland says the idea of mirror stars and a dark universe is âplausibleâ. However, if mirror stars ever existed, they would have had shorter lifetimes than regular stars, so they might not have persisted up to now. âThe density is lower in the mirror world,â he says. That means such stars would have used up their fuel more quickly, with lifetimes 10 times shorter than regular stars, and formed dark matter equivalents of black holes or neutron stars at the end of their lives. âMost of the mirror stars should have disappeared by now,â says Mohapatra.
The idea of mirror stars and a mirror universe remains extremely speculative. âItâs a theory,â says Armstrong. âWe donât know these objects exist.â But upcoming telescopes might be able to search for them, such as the Vera C. Rubin Observatory in Chile, which will perform a wide survey of the universe starting in 2025 that is projected to discover many faint objects.
Another way to detect a mirror star might be to see its gravitational effect on light that passes through it. âIt can bend light on a small scale,â says Armstrong. âA telescope like Vera Rubin would be able to look for effects like that.â
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