I can't resist 
discussing what is probably the most 
famous supernova of the recent times. 
many of you are too young to remember 
this. 
But I was a graduate student in 1987 and 
the story of the supernova is part of my 
education, so I'll tell you about it. 
the story starts about 168,000 years ago 
when a blue super giant, a type B super 
giant collapsed in a large magellanic 
clowd, the fact that the collapsing star 
managed to make it back from red giant to 
blue giant was 
surprising to theorists. But because this 
supernova occured so close to the solar 
system and the nearby large magellanic 
cloud, in fact, the progenitor star being 
a giant star was very luminous and was 
known and had been observed and this is I 
think the only case where we have 
observations of a star before and then of 
the supernova, remember, stellar 
evolution is by and large a slow process. 
This is one of the few cases where we 
really get to see a before and after 
image of the same star and you can study 
it and this forced some modifications to 
theory. 
the light from the supernova reached us 
in 1987 and it was the first supernova 
observed in 1987, so it was 1987A. And 
the remnants of the supernova are still 
under careful observation, we're still 
seeing the development. 
the sequence of Hubble images starting 
from 1994 and ending in 2006 shows you a 
ring-like structure, we'll just talk 
about it, around the supernova. 
the center is the remnant and then this 
ring which is progressively becoming more 
and more glowing and developing this 
blob-like structure is an exciting thing 
to, to, to pay attention to. 
even more famous, you can see it in the 
left, you can see an image of the 
surroundings of the explosion, and then a 
close-up on the right-hand side, which 
shows you the ring that I mentioned 
before, as well as two larger rings. 
I think this was referred to as the 
three-ring circus when it was first 
observed. 
And it took a lot of work by theorists to 
figure out what it is that we are seeing. 
the model that describes it is contained 
here. 
This was a large blue supergiant star. 
It had been experiencing mass loss. 
There was around it, this envelope, 
that is what this blue, 
haze there is attempting to describe in 
this rendition is the emission, 
remember, we talked about this the past 
emissions of the biploar emission of the 
star through mass loss prior to the 
supernova explosion. 
And what we're seeing where these two 
extreme rings on the left and right are 
at a distance of 20 light years from the 
supernova. 
These are glowing where the height, 
where the light from the supernova is 
hitting the ejecta from the previous mass 
loss. 
similarly, the glowing ring surrounding, 
the sort of waist of the hourglass, is an 
area where ejecta from the supernova, 
matter from the supernova, traveling much 
more slowly is now crashing in. 
The remnants of the star's atmosphere is 
now, are crashing in to the previously 
existing gas from previous mass loss and 
that's heating and compressing them, 
and that is the glow that we are seeing. 
And as I said, all of this is under a 
study but this was not even, but all of 
this for all its excitement, was not the 
most exciting aspect to me of supernova 
1987A. 
Yes, we were back to those 
Neutrinos. 
So, what transpired is that neutrino 
detectors, although they were not 
designed to be neutrino detectors were 
active at the time, they were looking 
actually for signals of proton decay and 
found none. 
But the people who were looking for 
proton decay had large tanks of water 
that they were observing for small 
flickers of light which we now know to be 
a very good way to detect neutrinos and 
it transpired in the weeks after the 
detection of the light from supernova 
1987A is that a burst of neutrinos, a 
total of 20 or 21, in three detectors 
worldwide 
were detected at about the time the 
supernova exploded. 
And you can again remember that 
remembering that most neutrinos go 
through most detectors completely without 
interacting the fact that we saw 20 of 
them, you can figure out how many 
actually have to go through the tank in 
order for 20 to be detected. 
You multiply that by the 4 pi r squared 
for 160,000 light years away which is 
where the 
neutrino exploded and you realize that 
this means the supernova admitted about 
ten to the 58 neutrini which since we 
know their average energy would have 
carried ten to the 46 joules, this was a 
subluminal supernova. 
it's a little it was a little bit 
less than luminous than a typical type 
two supernova. 
The reason for this as we now understand 
having seen the progenitor, is because 
this was a blue giant star. 
It had gone horizontal branch. 
It had shrunk the ejecta. 
had to escape a deeper gravitational 
well, they were more tightly bound. 
This was not a star, typically when we 
modeled supernovi, we were talking about 
red super giants, very bloated, most of 
the atmosphere is at large distances. 
In this case, all of the atmosphere would 
have had to have been blown away from 
very close relatively to the star's core 
and this means that less energy was 
available to escape in the supernova. 
And then, the fun thing about these 
neutrinos is when you track exactly when 
they were detected. 
They were detected about three hours 
before the light was detected. 
Now, neutrinos, I said, are not quite 
massless but they are almost massless, 
they travel essentially at the speed of 
light but they certainly travel no faster 
than light. 
incorrect news from a couple of years 
ago, notwithstanding. 
The reason neutrinos arrived prior to the 
light is that the density in the shock 
wave the supernova explosion, the 
compression is so extreme that for the 
first three hours light cannot escape 
but neutrinos escape first. 
So, the neutrino sphere breaks first, 
neutrinos has escaped. 
The ejecta have to thin for three more 
hours before light ceases to be trapped 
and so measuring this time difference, 
gave us a very good handle on checking 
the, our models of supernova and many 
things were verified and other things 
have been corrected since. 
this discovery, in sort of inadvertent 
launched a new field called neutrino 
astronomy. 
There are many new experiments planned to 
try to study the sky just as we learned 
new things when we turned on radio 
telescopes and x-ray telescopes and gamma 
ray telescopes. 
it is hoped that observing the universe 
in this, for essentially the first time 
in this non-light radiation, 
non-electromagnetic radiation will give 
us a handle on phenomena that have not 
previously been observed. 
there are many neutrino experiments. One 
of the most fun ones to think about is 
this experiment called ice cube, so to 
conduct a modern neutrino experiment, you 
take a tank a very, very pure water, the 
water has a lot of protons and electrons 
in it and if you happen to have a 
neutrino passing by, well, mostly nothing 
happens, but if it happens to interact 
with an electron, that electron or the 
products will be moving at a high speed 
through the tank and they will emit a 
characteristic, radiate a kind of light 
called Cherenkov radiation and then you 
put in light detectors called 
photomultipliers to detect the radiation. 
So, all you need is a great big tank of 
very pure water with a lot of 
photomultipliers attached to it. 
and you need to hide this deep 
underground because otherwise, cosmic 
rays and various kinds of contamination 
on the surface will, will overwhelm the 
neutrino signal so you hide it deep 
underground where only neutrini can get. 
And one of the best place to do, places 
to do this is actually in Antarctica, 
near the south pole. 
It turns out that polar ice, ice is not 
particularly transparent as we know it, 
but if you compress it, all of the 
impurities, it turns out are squeezed 
out, deep amount hundreds of meters below 
the surface, polar ice is very, very 
transparent. 
So, you have, ready-made, a deeply 
submerged huge collection of very pure 
water. 
And what the ice cube project is doing is 
lowering a bunch of photomultipliers. 
Here's a, a depiction of the grid into 
Antarctic ice and hooking them up to 
computers to try to detect neutrinos. 
And this is one of the more unusual and 
one of the more interesting telescopes 
that we have in the world. 
And since I was there for the actual 
excitement, I had to share this story 
with you.