When it comes to astronomy, it's easy to get lost among the stars and planets and galaxies
- some of the biggest things in the universe.
But small things can be important too, so some astronomers spend their time way down
at the smallest sub-atomic level, studying some of the tiniest known particles like neutrinos.
Neutrinos are tiny electrically neutral particles that are produced by extreme nuclear reactions,
like those that happen in the core of of the sun or an exploding star.
They are so small, in fact, there are actually trillions of neutrinos passing right through
the earth and you at any given moment, including right now and now and now!
But despite their prevalence, they are really hard to find.
Not only do they have a million times less mass than an electron, which is an extremely
unmassive particle, neutrinos also have no electric charge, so they don't interact with
charged particle in any way.
So astronomers have built enormous detectors all around the world in an effort to catch
a handful of these things at a time.
Why?
Well, because neutrinos are the most direct way to learn about reactions that are happening
deep inside of objects that we cannot observe first-hand, like the core of the sun, or supernovas,
even black holes.
Celestial objects like these all have one thing in common: lots and lots of energy which
results in plenty of intense nuclear reactions.
And different kinds of nuclear processes produce different kinds of neutrinos.
We've learned enough about neutrinos over the years to figure out which kinds are formed
by which types of reactions.
The trick is just spotting them.
Luckily, neutrinos can be detected.
When they buzz by particles like protons or electrons in just the right way, they produce
distinctive flashes of light called Cherenkov radiation.
In order to detect these tiny flashes, scientists set up huge tanks filled with the transparent
medium and then surround them with light sensitive detectors.
Now they can't just fill these tanks with air because neutrinos don't produce enough
energy to create that flash if and when they happen to interact with atoms in the gas.
But lots of kinds of liquids do the trick, so scientists often use water, mostly because
it is cheap, transparent and plentiful.
And that's how scientists built Kamiokande II, a detector deep in an underground Japanese
minefield with more than 3,000 tons of water, which helped detect the first-ever neutrinos
from a supernova.
On February 24th, 1987, astronomers spotted an especially violent type of supernova called
a core collapse supernova just 168,000 light-years from earth.
During these kinds of explosions, about 10^58 neutrinos are produced in just 10 seconds;
blasting out in space before the light from the explosion can escape the disintegrating
star.
So scientists checked the neutrino detectors and found that they'd caught about 20 neutrinos
from that supernova, all splattering in within a few seconds, as the blast wave raced past
earth.
This was a big breakthrough in our search for neutrinos.
For the first time, we knew that we could actually detect such remnants of distant,
ancient explosions, and the data helped scientists finally pinpoint the range of mass that these
tiny particles had.
But neutrinos can come from sources even farther away like super-massive black holes in far-off
galaxies.
In these cases, the high-powered magnetic fields around black holes can throw nearby
particles into overdrive, and if everything lines up right, these particles collide with
gas clouds, producing neutrinos, some of which head straight toward Earth.
Those exotic particles are among the types that scientists are searching for with IceCube,
one of the biggest neutrino detectors on the plant.
IceCube is actually a giant cube of ice in Antarctica; one cubic kilometer, to be exact,
threaded with more than 5,000 detectors that are super sensitive to Cherenkov radiation.
In 2013, IceCube detected 28 neutrinos, and each one had more than a million times as
much energy as the neutrinos created by the sun.
Based on their incredibly high energy levels, most of them seem to come from outside the
solar system.
Some even appeared to come all the way from outside our galaxy.
Now, neutrino astronomers are looking to the future, with designs for even bigger detectors
that can study more exotic phenomena; things with intimidating-sounding names like neutron
star collisions and dark supernovae.
So even though neutrinos are difficult to catch the small handful that we capture here
on earth, let us peer straight into the heart of the most energetic and violent objects
out there in the universe.
Thank you for watching this episode of SciShow Space.
If you'd like to keep exploring the universe with us, you can go to youtube.com/scishowspace
and subscribe.