BRIAN: All right, Paul.
That's pretty neat.
So someone on earth probably got a little flash of light
in their eye-- Cherenkov radiation, as we call it--
when one of the neutrinos from Supernova 1987A
went through and interacted with their sclera-- with the stuff in their eye--
they saw a little flash of light.
But--
PAUL: No one reported this.
And probably good chance they're asleep.
Or just one flash went off-- looking around, you wouldn't be noticed.
So it would be nice to have a better way to actually measure these neutrinos.
Maybe we don't need billions of eyeballs.
Maybe we should just have one very large tank of water.
BRIAN: Well, fortunately, it turns out that physicists
had foreseen that they needed big tanks of water to look at neutrinos,
specifically to understand why there weren't as many neutrinos coming out
of the sun, as we expected.
And so, there were some big tanks of water-- the largest of which
is known as Super Kamiokande II in a mine in Japan.
And it's this huge underground tank of water.
And it's underground, so that nothing else can get through.
So all the other particles and things of nature can't go through and interact.
Only things that weakly interact.
And in this big tank of water, there are these big photo multiplier tubes.
They're very sensitive to light.
And what you can't-- well, you can see how big these things are.
I think, I have two people here, as the water's being floated up.
So these are giant balls, about that big.
This thing is one of the biggest machines that we've made on earth.
And so this is like all of humanity's eyeballs.
And it was operating in 1987, on February 23rd,
the day before the Supernova 1987A was discovered.
And when they went through and looked at their results,
they saw that there were 12 flashes of light
in a very short period of about 15 seconds
a day before the supernova was discovered.
And that, we think, is the creation of the neutron
star associated with Supernova 1987A.
There was also a detector in South Dakota of the United States
that also detected 8 events.
So, confirmation.
PAUL: Yeah, as an interesting aside, there's
sort of bragging rights in astronomy about how
many photons you need to publish a paper.
And this, gravity waves would win.
Because they've got thousands of papers an no detection of anything yet.
But in this case, we've got 12 neutrinos, and another 8.
And how many papers would you say have been published based on those?
BRIAN: Oh, 100s, 100s.
This is really the mainstay of my field, understanding
how these neutron stars are formed, and how supernovae explode.
Now, we have all these neutrinos.
And as we've seen in our calculation, these neutrinos
are able to interact inside the centers of these massive stars near the neutron
star.
So life is complicated.
You need to actually do a big model to see what things look like.
So let's look at what one of these calculations
look like, where we've gravity coming in and neutrinos.
And they interact and form this big ball of stuff
that wobbles around, but doesn't seem to explode.
PAUL: Hmm.
I didn't see any explosion there.
I saw a lot of violence and chaos and turbulence.
But nothing went out.
BRIAN: Yeah.
So this turns out to be one of the hardest calculations we attempt
as scientists, where you have to have all this material coming in,
using general relativity.
Things are very, very hot.
And they're in states that we don't understand very well on earth,
because we can't make things this hot on earth.
And you have neutrinos whose properties aren't that well understood.
Because--
PAUL: They're so hard to measure.
BRIAN: --they go through everything, right?
And so, when we put all this stuff together,
we get something that almost explodes.
Turns out, occasionally explodes, when you
have a very small star that doesn't have much potential energy, compared
to a great big star.
That bounce does seem to get things far enough
away that the neutrinos can take over.
And the energy the neutrinos deposit is enough to blow those things up.
But that's only a few stars out of many attempts that explode.
So we seem to have a problem.
