For the first time ever, astronomers have detected a high-energy neutrino coming
from a supermassive black hole at the center of a blazar 4 billion light years
from Earth. Hi everyone, I'm Christian Reddy, your friendly neighborhood
astronomer. Welcome to launchpad astronomy where we
help make sense of the universe and our place in it. Now the interwebs were
buzzing last week with news about a neutrino coming from a blazar four
billion light-years away. Most people reacted with "Cool! What
exactly is a neutrino and what's a blazar and why our astronomers so
excited about all this?" So neutrinos are byproducts of
thermonuclear reactions such as those that are taking place in the Sun right
now. The Sun fuses protons together to form helium but also creates things like
gamma rays, positrons, and neutrinos in the process. Now the neutrinos are almost
but not quite massless. They have a tiny amount of mass, about a millionth the
mass of an electron, and they can travel through space at speeds that are
essentially the same speed as light. Like photons of light they pack a certain
amount of energy. The closer they travel to the speed of light, the more energy
they're packing. And neutrinos are ghosts. They are called the ghost particle. They're
space ghosts. they can go coast-to-coast without so much as touching another
particle. They're like the ninjas of the universe and there's a hundred trillion
of them passing right through you every second. They pass
through the Earth, they pass through stars, they pass through entire galaxies
undetected because they just don't knock into other particles. Except once in a
while, a single neutrino, perhaps one in 1 million trillion neutrinos will strike a
proton or an electron and create a new particle. The IceCube neutrino
Observatory underneath the South Pole is the world's largest neutrino detector.
It's a full cubic kilometer of detectors strung into the
ice a kilometer underground. But on September 22nd 2017, Ice Cube detected a
neutrino as it slammed into an atom and created a new particle called a Muon.
Now this muon particle travels forward in the same direction as the neutrino
was coming from, but as it does so it travels faster than light inside the ice.
Now how can something travel faster than light? Well remember the speed of light
that we talk about is the speed of light in a vacuum. But when light enters
into, say, water or ice, it travels about 24% slower, so the muon can easily
outpace it. This creates a cone of blue light called Cherenkov radiation which
is the optical equivalent of a sonic boom. Detectors measure the radiation
created by the impact and found that this neutrino is packing 300 trillion
electron volts of energy. To give you a point of reference. the Large Hadron
Collider can accelerate protons until they reach six and a half trillion
electron volts of energy, so this neutrino had something like 46 times
more energy than we can create in the largest particle accelerator on Earth. In
less than a minute, IceCube's computers traced the neutrino's
path through the detector all the way back to the left shoulder of Orion.
Within hours, NASA's Fermi Gamma-Ray Space Telescope caught a blast of gamma
rays coming from a blazar named TXS 0506+056, which coincidentally was
the name of my high school death metal band. Ok, so what's a blazar? Well, a blazar
is a type of galaxy with a supermassive black hole at its center. And by
'supermassive', I mean several hundred million times the mass of the Sun.
Matter spirals into the black hole. As it spirals in, it heats up and generates a
tremendous amount of energy, some of which is channeled
into a bipolar jet. If one of those jets happens to be aimed toward Earth, then
that object is going to be extremely bright in the sky, particularly at x-ray
and gamma-ray wavelengths. So we call these types of ultra-bright objects
"blazars." Now, Fermi have been detecting gamma rays coming from this blazar for
about a decade. But around the same time that IceCube detected this very
high-energy neutrino, Fermi also detected a surge of gamma rays coming from the
same blazar. But Fermi's observations were quickly confirmed a few days later
by the Major Atmospheric Gamma Imaging Cherenkov, or MAGIC telescopes. These
telescopes don't actually see gamma rays but instead they detect a shower of
Cherenkov radiation as high-energy gamma rays from the same blazar are slammed
into the atmosphere. And this is exciting because it's the first time we've
directly traced a neutrino all the way back to a black hole. And in fact it's
the first time we've detected a neutrino coming from a source beyond our Milky
Way galaxy. The last time we detected neutrinos coming from a source other
than our Sun was 30 years ago when Supernova 1987a exploded in the Large
Magellanic Cloud. But Supernova 1987a is only 150,000
light-years from Earth. But this neutrino was detected from a blazar that is 3.9
billion light-years away! Now since this blazar was already a
known source of gamma rays, the IceCube team went back in their data to see if
there were any neutrinos that might have come from the same source. Sure enough
they found several lower energy neutrinos that were in fact coming from
the same blazar. So how cool is that? We now know that blazars are a source of
cosmic neutrinos. But another reason this is exciting is because it helps to
explain another kind of phenomena called Cosmic Rays. Now cosmic rays are really. -
they're just protons, so they're actually charged particles. Nevertheless we call
them "rays" because we give bad names to all kinds of things in
astronomy, so what are you gonna do? But the cosmic rays are highly charged
protons. They're accelerated to very high speeds, and they pack a ton of energy, but
even though cosmic rays were discovered over a hundred years ago, astronomers
haven't been able to figure out where exactly they come from. And that's
because cosmic rays carry a charge and charged particles are deflected in the
presence of magnetic fields. And this means that we have no way of really
knowing where they came from. But a source that produces cosmic rays will
also produce neutrinos in the process, and since neutrinos are neutral in
charge they ignore magnetic fields and can travel in straight lines through
space, just like a ray of light. That means that even though we can't look at
an individual cosmic ray and know its particular origin, we can now say that
blazars are also a source of cosmic rays! And this story goes way beyond neutrinos
and gamma rays and cosmic rays. There were follow-up observations
conducted at optical and infrared and radio wavelengths, all trying to build up
a picture of just what's going on inside this blazar. And that's another reason
why this story is very exciting in astronomy, It means that we're able to
use not just multiple wavelengths of light, but also multiple messengers. We
can now detect gravitational waves and neutrinos, so we can use signals that go
beyond the electromagnetic spectrum to understand how the cosmos works. Okay, wow,
that was a lot to unpack. I know there was a whole lot of jargon in this video;
please feel free to watch it again and by all means leave a comment if you have
any questions or clarifications, corrections, even. Hopefully I didn't get
anything wrong, but we'll see. and if you have any thoughts on this particular
subject or anything else you'd like to know about, please make sure to let me
know in the comments below. Now if you want to know more about the
electromagnetic spectrum and radiation and how telescopes work, I have a couple
of playlists here that I'll share with you and I'll make sure I've got links of
them in the description below. So thank you very much for watching, keep watching
the skies, and we'll see you next time. Hi everyone...birds. Hi everyone, I'm
Christian Ready... they're gonna be doing that for a while, I might just have to
just power through it. [BEEP] And why are astronomers so excited about all this?
....Cicadas. Cicadas are getting it on.