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What's mysterious, invisible to scientists until it interacts with something, and responsible for some of the dark matter in the universe? Black Holes Neutrinos Particle accelerators aren't the only way to produce neutrinos, as we all know everything from the Sun to entire galaxies and even bananas produce neutrinos. But what about objects so massive that nothing, not even light, can escape?
To black holes create neutrinos? Yes, but not in the way you might expect. That's Regina Caputo, a NASA scientist studying gamma-ray astrophysics. Hi Kirsty! Black holes get their name because nothing, not even the fastest thing in the universe, light, can escape their gravitational pull. Even though neutrinos rarely interact with matter, they do get affected by gravity. So neutrino wouldn't be able to emerge from beyond the event horizon of a black hole.
Let's hit pause on the neutrino discussion and go over some black hole basics. What most people think of when they picture a black hole is actually the event horizon, the point of no return. And at the very center of the black hole lies the singularity, where matter has collapsed into a region of infinite density. From here to the event horizon is a mystery to us. We have no way to observe anything going on in that region. Around some black holes is an accretion disk, the glowing ring formed by matter spiraling towards a black hole. Some of that material gets sped up close to the speed of light and flung out into space in twin jets.
Black holes also come in three types. Stellar mass black holes are, as their name suggests, the massive stars. These are formed from massive stars collapsing in on themselves and some stellar mergers. Then we have supermassive black holes, which we think sit at the heart of almost every galaxy. The third type is intermediate mass black holes, which we think might be the missing link between stellar mass black holes and supermassive black holes. There's also primordial black holes, but we don't have time to go down that hypothetical rabbit hole. OK, now back to our regularly scheduled neutrino content. While neutrinos don't come from beyond the event horizon, we have seen neutrinos from black holes.
In 2017, NASA's Fermi Gamma Ray Space Telescope traced a high-energy neutrino discovered by the IceCube Neutrino Observatory back to a galaxy 47 million light years from Earth. At the heart of this galaxy, called Messier 77, or the squid galaxy, lies an extremely active supermassive black hole. You can kind of think of black holes like the mouths of the universe. If a star gets too close, they'll gobble it up. Some galaxies, like the Milky Way, for example, have a dormant supermassive black hole, meaning it's not snacking on anything.
Other galaxies, like the squid galaxy, have a supermassive black hole devouring nearby material. This results in an accretion disk around the black hole and the relativistic jets I mentioned before. When those jets are pointed at Earth, we call that supermassive black hole a "blazar." And because black holes tend to be messy eaters, even a relatively quiet supermassive black hole, like Sagittarius A star, might start sending out neutrinos if a star wandered too close. A few years ago, scientists detected a neutrino signal that might have come from one such tidal disruption event. But on further analysis of the energy of the neutrino was possibly too low to come from that TDE.
The most famous source of cosmic neutrinos is supernova 1987a. While that supernova didn't leave behind a black hole, we would be able to determine if a supernova remnant was a neutron star or a black hole based on the neutrino signal we receive. That's right! Fans of this show will remember that I covered this topic in this video. Physicists caught a few neutrinos from 1987a with the KAMIOKANDE II and IMB experiments. The Fermilab-hosted Deep Underground Neutrino experiment will be able to pick up neutrinos from any galactic supernovae. And if the neutrino signal from that source suddenly cuts off, we'll know we've found a baby black hole.
Aww, so cute! We haven't seen any yet, but there's a chance that we could also potentially see neutrinos from a black hole neutron star merger. But these events would take place extremely far away, so we wouldn't see very many neutrinos and would need a much larger detector the size of Icecube to catch them. We're just beginning to scratch the surface of a revolution in multi-messenger astrophysics. For centuries, astronomers have only been able to access photons. But now we have access to gravitational waves and interstellar neutrinos, which is so exciting because while light can get deflected, neutrinos and gravitational waves can travel relatively unaffected through space. So of that note, what can neutrinos
possibly tell us about black holes? For supernovae, neutrinos can act as an early detection system. They can escape a supernova before anything else can. So if we see a bunch of neutrinos coming from one area of the sky, neutrino scientists can alert astronomers to point their telescopes to that region. These neutrinos would also be documenting the final moments of a massive star's life and could potentially tell us a lot about stellar processes, the energy output from a supernova, and maybe some information about the kinds of elements created. And of course, depending on the signal, we'd be able to tell if a black hole was left behind. In turn, a supernova could help shed light on the mass of a neutrino.
Neutrinos likely won't be able to tell us very much about black holes themselves, but they can tell us a lot about the environment and mechanics surrounding a black hole. We don't really understand how the jets form or why they're located on the black hole's axis. We don't know much about the material the jets are composed of, so if we see neutrinos coming from a jet, that's a smoking gun that protons are somehow involved. Sounds like black holes are just as mysterious as neutrinos. Thanks Regina. Thanks Kirsty. So there you have it. The most massive objects in the universe and the lightest massive particles are more similar than you might think.
Both are enigmas that scientists are working to understand. Like, share and subscribe to come along, and let me know in the comments what's your favourite fact about black holes? Fun fact! The Milky Way's supermassive black hole, Sagittarius A*, is 4.3 million times the mass of the Sun. The most massive black hole astronomers have discovered is Ton 618, and it is 66 billion solar masses.
