Neutrinos from a supernova could help unlock dark matter

Neutrinos from a supernova could help unlock dark matter

The next supernova to occur in our galaxy could be the key to unlocking one of the universe’s biggest mysteries: dark matter. This type of event releases an enormous amount of energy in the form of neutrinos and, perhaps, particles that make up dark matter.

  • Supernovae can extinguish life on distant planets
  • ‘Hidden’ supernova remnants in the Milky Way are found

Supernovae in our galaxy are common on a cosmic time scale, but rare for a human lifetime. The last supernova with the naked eye of the Milky Way happened in 1604, while the most recent one – not visible because it occurred in the galactic nucleus – occurred in 1898.

On average, stellar explosions in galaxies like ours happen once every century, so there’s a chance we’ll see a supernova in the coming decades. There is still no concrete prediction for such an event later this century, except for a probability for V Sagittae, which could explode in 2083.

Regardless of which star explodes first, the phenomenon will provide astronomers with a unique opportunity to detect an abundant amount of neutrinos, known as “ghost particles”. The nickname is an allusion to the small rate of interaction between neutrinos and other particles in the universe.

Supernovas and Neutrinos

The fact that neutrinos don’t interact with “ordinary” matter means they can pass through stars, planets, and even humans. In fact, they do it all the time! Thousands of neutrinos emitted by the Sun are passing through your body right now.

On the other hand, this also means that these particles are extremely difficult to detect. To observe a few dozen of them, scientists need very specific detectors, like the IceCube, buried in Antarctic ice.

Neutrinos can be emitted by various bodies, such as distant stars, our Sun, and even the Earth’s core. However, in some cases, they can gain much more energy — one such case is when particles are emitted by a supernova explosion or a black hole.

In 1987, for example, a supernova occurred outside the Milky Way, in the Large Magellanic Cloud galaxy. From the explosion, a stream of high-energy neutrinos was emitted, some of which hit three detectors on Earth. The amount, however, was not so impressive: just over 20 neutrinos, for about 12 seconds.

Still, the detection marked the birth of neutrino astronomy from such events. At that time, there wasn’t a detector specifically made to detect ghost particles, so the devices at the time really did a great job.

Neutrinos and dark matter

Dark matter is by far the biggest component of the universe, but we still don’t know what it’s made of. There are some hypothetical particles that scientists have described and then tried to find, but so far none have been observed.

Like neutrinos, dark matter does not interact with ordinary matter except through gravity. It is thanks to its great gravitational force exerted on galaxies that astronomers can say that dark matter really exists.

But how do you observe something that doesn’t interact with light or any other known particle? This is the really tricky part, as all scientific instruments rely on existing types of “light” (visible light and other wavelengths of the electromagnetic spectrum) or on interaction with other Standard Model particles.

Therefore, every direct detection method ever used to observe dark matter depends on some interaction with some kind of normal matter. These methods aren’t exactly bad; is that this is the only kind of interaction that current physics allows.

Furthermore, it may be that dark matter only interacts with ordinary matter through extreme physical processes in the universe, impossible to reproduce in laboratories. In this case, we can only rely on such cosmic events.

This is where supernovae within the Milky Way come into play. There are reasons for scientists to think that, perhaps, dark matter is, along with neutrinos, the carrier of the energy released by the explosion of a massive star.

When astronomers detect a supernova, what they observe are the waves of the electromagnetic spectrum, such as visible light, X-rays, gamma rays, among others. But most of a supernova’s energy is carried in the form of neutrinos. And, unlike light, they can pass through all of a star’s matter instantly, since they can’t be blocked by anything.

A type II supernova (from stellar core collapse) releases about 99% of all its energy in the form of neutrinos. It is this process that usually leads to the implosion of the core and the formation of a neutron star or black hole.

With modern detectors, if a core-collapse supernova were to explode inside the Milky Way today, we could detect as many as tens or hundreds of millions of neutrinos. Scientists know this because the physics of supernovae are well understood, so it is possible to predict how many neutrinos will be produced when this occurs.

The interesting part for dark matter hunters is that these predictions may not come true. This would certainly happen if dark matter also carries some of the energy released by the supernova. In other words, if the amount of neutrinos from a supernova is less than expected, dark matter could be there too.

a new physics

If neutrinos are supposed to carry 99% of the energy of a core-collapse supernova, that’s exactly what scientists should find in the detectors. If a small percentage of that energy is carried by dark matter, researchers will find a neutrinos deficit.

That would be a victory in the search for the unknown particle that makes up dark matter. If it can carry the energy of a supernova, the discovery should point the way to the development of experiments actually able to detect it directly.

For this, it is necessary that the supernova occurs in our own galaxy, because only then can a substantial amount of neutrinos reach the detectors. Unfortunately, V Sagittae will not be a Type II supernova — in fact, it will likely be a nova, a type of explosion caused by the accretion of hydrogen to the surface of a white dwarf.

The possibilities of a supernova sending exactly the expected amount of neutrinos are very high, since this is the prediction of the Standard Model of particles. This model is, to date, the most successful for explaining quantum physics, so anything outside of that will mean completely new physics.

It’s not common to find new physics in the universe, but scientists are hoping for this to happen. After all, as good as it is, the Standard Model does not explain everything, even more so when the subject is dark matter. Therefore, expectations for a supernova to occur nearby are high and it could mean a real revolution in physics.

Source: Starts With a Bang