The supernova remnant W44 glows purple when powerful cosmic rays collide with gas. Scientists are trying to figure out where the most intense cosmic rays in the universe come from — and a new study offers an unusual answer. (Image courtesy of NASA Goddard)
The strongest cosmic rays hitting Earth may not be the result of events in distant parts of space, but rather come from heavy dark matter particles annihilating near us.
Cosmic rays are high-energy particles that continually zip through space. They are mostly made up of protons, but sometimes include nuclei of heavier elements like helium and even iron. Despite their tiny size, their impact is significant. Each particle travels at nearly the speed of light, and the fastest of them have energies trillions of times greater than our most powerful particle acceleration machines.
Astrophysicists know the origin of most cosmic rays. Every time a high-energy event occurs in space, it is likely to produce a stream of cosmic rays. This can happen in supernova explosions, merging stars, or black holes swallowing matter.
However, the origin of the most powerful cosmic rays remains unclear. The problem is that although there are many possible energy sources, they are billions of light years away. These super-energetic particles cannot travel such vast distances without losing significant speed. Therefore, their sources may be much closer to us.
And their origins may be far more exotic than a simple cosmic explosion. In a recent paper, not yet peer-reviewed, a Russian astrophysicist suggests that the most powerful cosmic rays come from an exotic form of dark matter.
Heavy, dark and self-destructive
This dark matter particle would be extremely heavy — significantly heavier than even the heaviest known particle, the top quark. Called a scalaron, this dark matter particle would have been created in the earliest moments of cosmic history, during an era known as inflation, when the universe dramatically expanded in size in an instant.
Since then, the scalaron has remained largely unnoticed, as it does not interact with light and affects the rest of the universe only through its gravitational influence. However, on rare occasions, two scalarons can cross paths – and in the process, annihilate each other with a release of energy. This outburst can produce extremely energetic cosmic rays.
Scalarons are everywhere, allowing them to create ultra-high-energy cosmic rays inside our galaxy. But it’s important that the theories match the observed data. If scalarons interact too often, they will create more high-energy cosmic rays than we observe. Conversely, if they don’t intersect and annihilate often enough, it won’t be consistent with known observations.
Thus, annihilating scalarons could explain the number of high-energy cosmic rays we detect; the densities and frequency of interactions are consistent with the known behavior of dark matter.
However, this is only a low-probability hypothesis. The formation of scalarons in the early universe requires a correction to Einstein's general theory of relativity that may not hold up to further study. In addition, there are alternative theories to explain high-energy cosmic rays. For example, they may originate inside molecular clouds in our galaxy, without the need for dark matter.
In any case, it’s an interesting concept that demonstrates how the extremes of our universe can serve as a testing ground for radical ideas. By exploring these concepts further, we may find other ways to confirm them observationally. And if this idea turns out to be correct, it will give us access not only to dark matter, but also to the very early history of the universe.
Sourse: www.livescience.com
