2024-03-29 12:50:17
Dark matter affects cosmic behavior through gravitational interactions, leading to phenomena such as “dark stars,” which can explode similar to supernovae. The investigation of potential dark matter particles, such as WIMPs and axions, is critical to understanding these celestial events. Credit: twoday.co.il.com
Dark matter, which affects the universe through gravitational interactions, remains elusive with potential forms such as WIMPs and axions, the latter potentially creating explosive “dark stars”.
Dark matter is ghostly matter that astronomers haven’t been able to detect for decades, yet we know it has a huge effect on the normal matter in the universe, like stars and galaxies. Through the massive gravitational pull it exerts on galaxies, it spins them, gives them an extra boost along their orbits, or even tears them apart.
Like a cosmic carnival mirror, it also bends the light from distant objects to create distorted or multiple images, a process called gravitational lensing.
And recent studies show that it may create even more drama than that, by producing stars that explode.
The journey to detect dark matter
For all the havoc it wreaks on galaxies, not much is known about whether dark matter can interact with itself, other than through gravity. If he experienced other forces, they must be very weak, otherwise, they would be measured.
A possible candidate for the dark matter particle, consisting of a hypothetical class of weakly interacting massive particles (or WIMPs), has been intensively studied, so far without observational evidence.
Recently, other types of particles, also weakly interacting but extremely light, have become the focus of attention. These particles, called axons, were first proposed in the late 1970s to solve a quantum problem, but they may also be suitable for dark matter.
Axion and the Cosmic Dance
Unlike WIMPs, which cannot “stick” together to form small objects, axions can. Because they are so light, a huge number of axons would have to account for all the dark matter, which means they would have to be packed together. But because they are a type of subatomic particle known as a boson, they don’t care.
In fact, calculations show that axions can be packed so closely together that they start to behave strangely—acting together like a wave—according to the rules of quantum mechanics, the theory that governs the microscopic world of atoms and particles. This state is called a Bose-Einstein condensate, and it may, unexpectedly, allow axions to form their own “stars.”
This will happen when the wave moves on its own, creating what physicists call a “sultan”, which is a localized lump of energy that can move without distorting or dissipating. It is often seen on Earth in eddies and eddies, or in the bubble rings that dolphins enjoy underwater.
The new study provides calculations that show that such solitons will eventually grow in size, becoming a star, similar in size to or larger than a normal star. But finally, they become unstable and explode.
The energy released from one such explosion (known as a “bosnova”) will rival that of a supernova (an ordinary star exploding). Given that dark matter far outnumbers visible matter in the universe, this will surely leave a mark on our observations of the sky. We haven’t found such scars yet, but the new research gives us something to look for.
Observational prospects and theoretical developments
The researchers behind the study say that the surrounding gas, which is made of ordinary matter, will absorb this extra energy from the explosion and emit some of it back. Since most of this gas is made of hydrogen, we know that this light must be at radio frequencies.
Excitingly, future observations with the Square Kilometer Array radio telescope will be able to pick it up.
This artist’s impression shows the Square Kilometer Array, an array of telescopes currently being built in Australia and Africa. Credit: SPDO/TDP/DRAO/Swinburne Astronomy Productions
So while the fireworks from exploding dark stars may be hidden from our view, we may be able to find their consequences in visible matter. What’s amazing about this is that such a discovery will help us understand what dark matter is actually made of – in this case, most likely exions.
What if observations do not detect the predicted signal? This probably won’t completely rule out this theory, since other “axon-like” particles are still possible. However, failure to detect may indicate that the masses of these particles are very different, or that they do not couple to radiation as strongly as we thought.
In fact, it has happened before. Originally, axions were thought to bind together so strongly that they could cool the gas inside stars. But since stellar cooling models showed that stars are fine without this mechanism, the axion coupling strength should have been lower than originally assumed.
Of course, there is no guarantee that dark matter is made of axions. WIMPs are still contenders in this race, and there are others too.
By the way, some studies indicate that WIMP-like dark matter may also form “dark stars”. In this case, the stars would still be normal (made of hydrogen and helium), with the dark matter only driving them.
These dark WIMP-driven stars are expected to be supermassive and short-lived in the early universe. But they could be observed by the James Webb Space Telescope. A recent study claimed three such discoveries, though the jury is still out on whether this is actually the case.
Nevertheless, excitement about axions is growing, and there are many plans to discover them. For example, axes are expected to become photons when they pass through a magnetic field, so observations of photons of a certain energy are aimed at stars with magnetic fields, such as neutron stars, or even the Sun.
On the theoretical front, there are efforts to refine predictions of what the universe will look like with different types of dark matter. For example, axons can be distinguished from WIMPs by the way they bend light through gravitational lensing.
With better observations and theories, we hope that the mystery of dark matter will be solved soon.
Written by Andrea Font, Reader in Theoretical Astrophysics, Liverpool John Moores University.
Adapted from an article originally published on The Conversation.
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