Dark matter is proving to be a rather frustrating subject for physicists, cosmologists, and other outward-looking scientists. All data on dark matter is gravitational, and the lack of other evidence only draws a box on the particle map where scientists have scribbled, “Here is dark matter.”
Dark matter interacts so weakly with ordinary matter that we simply don’t notice it above the din of ordinary matter shouting drunkenly at the particle bar of the Universe. What we need is to give him a place to shine, let him take the limelight and sing karaoke. It turns out that the interior of a star could just be this place.
Disappointing flashes in the dark
Most proposed dark matter candidates use the simplest possible extension of the Standard Model. These extensions allow theoretical physicists to estimate how these particles would interact with ordinary matter.
Based on these ideas, experimental physicists set up large reservoirs of xenon in the deepest, darkest holes they could find and surrounded the reservoirs with light detectors, looking for clues. rare events – dark matter colliding with ordinary matter. These are tightly controlled experiments, where every flash of light is analyzed. The non-dark matter chain reactions that lead to flashes of light are known and controlled.
So far, however, nothing concrete has emerged.
In the meantime, because we don’t really know what dark matter is, theoretical physicists have let their imaginations run wild. They created a zoo of possible dark matter particles. Standard Model extensions allow for almost anything, so there are proposals for atoms, molecules, and even stars made of dark matter. Yes, there could be an entirely invisible mirror universe that would hold our own universe together.
Exciting stellar flares
If it is true that dark matter can form structures, there are likely dark matter asteroids flying around the Universe. Sometimes dark matter asteroids collide with stars and then things get very exciting.
The dark matter of an asteroid interacting with the actual matter of a star is essentially unity (because stars are rather dense). From what we know about the Universe and galaxy formation, dark matter asteroids must be moving very quickly.
“Fast”, in this case, means “faster than the speed of sound in a star”. So when an asteroid hits a star, it produces a cylindrical-shaped acoustic shock wave. The star acts as an acoustic lens – a star is less dense and deflects acoustic rays towards the surface – so the shock wave is loosely focused around the asteroid’s entry point.
This process acts to intensify the shock wave in a local region rather than letting it spread. Then, as the shock wave gets closer to the surface, its speed (relative to the speed of sound) increases, increasing its effect on the stellar medium.
These two processes are sufficient for the star to emit a burst of X-rays, with an emission tail extending into visible light. In other words, there is a flash of light that is clearly visible to our observing tools.
Solar flares are common
The researchers used the estimated dark matter density of a globular cluster called 47 Tuc to calculate how often dark asteroid-induced flares would be visible to the Hubble Space Telescope (if it had the right filters in place). The scientists concluded that a week of observation should be sufficient to detect the eruptions. They then looked at the Hubble database and found that 47 Tuc had been observed for a week, but with the wrong filter in place. Unsurprisingly, he found nothing.
In addition to Hubble, the researchers also envisioned a soon-to-deploy wide-field UV space telescope. In this case, the researchers propose to look at K dwarfs (a set of relatively cool stars in the main sequence) that are local by astronomical standards. Indeed, if dark matter asteroids exist and behave as the researchers predict, this telescope cannot avoid detecting the resulting flares. So would all the others which are also designed to monitor large sections of the sky in the ultraviolet.
Even our own Sun would be prone to flares from dark asteroids. Researchers estimate that the Sun should collide with a small asteroid every year. The evidence – solar flares – may even already be in the sighting record.
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