2023-12-28 13:57:27
No matter how hard they have tried, scientists still don’t know what dark matter could be made of. And until now, no one, despite the tremendous efforts of recent decades, has been able to detect it directly.
We do know, however, some important things. For example, it is much more abundant than ordinary matter (five times more), which means it is practically everywhere, surrounding stars and galaxies. And we also know that, despite not emitting any type of light or radiation (which is why none of our instruments can detect it) it does respond and exert gravity. Which allows the matter that we can see, which is made of known atoms and particles, to stay together to give shape to stars and galaxies. In a way, and although we do not yet know what it is or how it ‘works’, dark matter can be considered the ‘skeleton’ of the Universe in which we live.
To try to explain the nature of this ‘other type’ of matter, scientists have already proposed all kinds of theories about its possible composition, from exotic particles such as axions, neutralinos, Wimps, or primordial mini black holes that emerged from the Big Bang to the idea that dark matter does not exist at all, and what we perceive is actually a consequence of the force of gravity not being the same everywhere.
A mirror universe
More recently, some scientists have proposed an idea that is certainly strange, but could work. In parallel to ours, this theory says, there is a ‘Mirror Universe’ that is the inverted image of the one we occupy. Said Universe would be composed of ‘atomic dark matter’, that is, dark matter versions of our conventional atoms and particles: dark protons, dark electrons, etc. etc.
“According to this theory,” explains Isabella Armstrong, from the University of Toronto in Canada and lead author of a new study that recently appeared in ArXiv– in that Universe there would be stars similar to the ones we see, like our Sun, but made of dark matter and emitting dark photons.”
These ‘mirror stars’ could grow up to ten times larger than the Sun, and would also have nuclear fusion in their fiery cores, where ‘dark hydrogen’ would fuse to give rise to ‘dark helium’. Of course, those stars would be invisible to us, as they would not emit any light or interact with the ‘normal’ matter of our own Universe.
But still, Armstrong and his colleagues write, there is a way to see them, since some of them could contain small fragments of ‘normal’ matter inside. For example, as one of these mirror stars moved through a galaxy, its gravity would attract the normal matter of the gas and dust nebulae it passed through. “And that gas – explains Armstrong – would begin to heat up and emit light.” A light that is visible.
Inside the invisible mirror star, the fragment of matter that we can see would look quite similar to a white dwarf, the bare core that remains at the end of the life of stars like the Sun. But unlike white dwarfs, he says Armstrong, this will emit a very notable signal of X-rays and visible light. “This is how we can differentiate them.”
If we haven’t already done it. Just a few months ago, in fact, a team of astrophysicists from the University of Texas at Austin, with the James Webb Space Telescope, located three objects which, in the absence of confirmation, could be the first dark stars observed by man.
The idea of the existence of mirror stars is plausible, but some researchers believe that their lives would be significantly shorter than those of normal stars, and that it is therefore very possible that all those that have ever existed have already disappeared.
Of course, the idea of a mirror Universe with dark stars that we cannot see is extremely speculative. “It’s just a theory,” says Armstrong, “and we don’t know if these objects really exist.” However, searching for them could be one of the tasks for the next generation of telescopes, such as the Vera Rubin Observatory, in Chile, which will begin operating in 2025 and which could observe the gravitational effect that light suffers when passing through one of these stars.
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