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According to a recent article, the Earth would be caught directly in the sights of a cosmic hurricane. A swarm of nearly 100 stars, accompanied by an even greater amount of dark matter, directly targets our stellar neighborhood and we can do nothing to stop it; in fact, the vanguard is already on us. It sounds like a perfect blockbuster movie in the summer, starring The Rock and Chris Pratt, or maybe Scarlett Johansson and Charlize Theron.
Except that's for real. But is it a danger? Well, actually, no. Not at all. But it's potentially incredibly fascinating, with many interesting scientific interconnections. So, what's really going on?
The story begins last April, when the Gaia satellite announced the locations and trajectories of 2 billion stars near the Milky Way surrounding our sun. They published the data to the public.
Scientists were then able to examine the dataset to see if they could detect anything particular. In galaxies such as the Milky Way, the most common behavior is that stars gravitate around the center of the galaxy in a similar way to planets orbiting our sun. However, some stars show unusual movement. About a year ago, astronomers identified "stellar streams" crossing our celestial neighborhood.
One of them, called S1 (for Stream 1), is composed of nearly 100 stars of similar age and composition, gravitating around the Milky Way in a direction exactly opposite to that normal stars. It's a bit like a handful of cars that roll in the wrong direction on the highway, except for a much larger distance separating them and a risk unequaled collision. These stars are spread over a few thousand light years and will cross the neighborhood of the solar system for a few million years.
Astronomers have identified S1 as part of the remnants of a dwarf galaxy that collided with the Milky Way and was consumed by an epic episode of cosmic cannibalism. Dwarf galaxies are very small and generally represent about 1% of the mass of the Milky Way. They can gravitate around larger galaxies and collide with the larger ones, adding mass to the parent. This is what seems to be happening in the case of S1, although the process has probably taken a billion years.
Dwarf galaxies often contain a disproportionate fraction of dark matter. Dark matter is a hypothetical form of the yet to be discovered material that interacts only by gravitation. Scientists have proposed its existence to explain many astronomical mysteries, for example, the observation that most galaxies revolve faster than the known laws of physics, the stars and gases that compose them.
Although dark matter has not yet been observed, the assumption of its existence is the simplest and most economical explanation of the myriad of astronomical mysteries. On the whole of the universe, it is thought that dark matter is five times more present than the ordinary mass of stars, gases and planets.
In dwarf galaxies, the fraction of dark matter is often higher. In Fornax, a well-studied dwarf galaxy orbiting the Milky Way, researchers estimate that dark matter is 10 to 100 times greater than the mass present in its stars.
If this number is valid for S1, the dark matter of the S1 flux crosses the Earth at a much higher speed than the more ordinary dark matter that gravitates around the Milky Way, about twice as fast. Dark matter S1 is believed to fly in the solar system at a speed of about 550 km / s, or about 1.2 million mph. Although these numbers are impressive, they are misleading. Dark matter, if it exists, is extremely diffuse and will have no discernible effect on the solar system.
Since dark matter has not yet been observed, these velocity values are speculative, although they are strongly supported by a very large body of evidence. However, the possibility that high-speed dark matter is flying across the Earth suggests an opportunity to detect it.
In an article from the prestigious journal Physical Review D, researcher Ciaran O & ## Hare and his collaborators have calculated the possibilities of discovery of dark matter using existing or proposed detectors. They considered two types of dark matter particles: a very heavy type called WIMP (massive particle with weak interaction) and a very light type called axion. Because the ultimate nature of dark matter is not known, it is important to be open to all possibilities.
They found that the detectors they had evaluated could find WIMPs for certain ranges of particle mass. However, when they examined the possibility of an axion, it appeared that the outlook was even better. Because of its light weight and the way an axion would interact with the detector, the device simply has a better chance of seeing the axion. (If the axions exist, of course.)
Experiments with names such as ADMX, MADMAX and ABRACADABRA are able or will be able to search for the dark matter signatures proposed in the recent document. They consist of technologies designed to interact with axions in a powerful magnetic field and convert them into ordinary microwaves or easily detectable radio waves.
It is important to remember that the S1 stream represents no credible threat to the Earth and humanity. There is no need for an action hero to save us. However, the synergy of science is staggering. A careful catalog of nearby stars has opened up the prospect of a better opportunity to find and identify dark matter, which is one of the great unanswered mysteries of modern physics. We are living in an incredible period in which we can study such things.
I'm excited.
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