“We should do astronomy because it is beautiful and because it is fun. We should do it because people want to know. We want to know our place in the universe and how things happen.” -John Bahcall
Of course you’re all going to watch the exciting Live interview with me on KGW tonight (streaming here; video should be posted after-the-fact here), but shouldn’t we give you some extra fun facts about neutrinos?
Here we go…
Both photons and neutrinos are created in the core of stars. But while photons take tens of thousands of years to reach the edge of the Sun, neutrinos make the trip in just over two seconds.
In 1987, the closest supernova in over 100 years went off in the Large Magellanic Cloud, 168,000 light years away. We detected 23 neutrinos from it; thus far, these are the only neutrinos ever detected from a supernova.
A typical supernova emits somewhere around 1057 neutrinos at once, about 1018 times the rate that our Sun emits them.
The last supernova observed within our own galaxy went off in 1604, at a distance of about 20,000 light years away. One of the best candidates for the next supernova in our galaxy to go off is Betelgeuse, which is only 640 light years from us.
Betelgeuse could go off any time in the next million years. The largest neutrino detector in operation today is Super Kamiokande-III in Japan, which houses 50,000 tonnes of water to interact with neutrinos.
If Betelgeuse went supernova today, Super Kamiokande-III would detect an estimated 13 million neutrinos.
A good neutrino detector, like OPERA (above, credit INFN), consists of more than 1,000 tonnes of mass for neutrinos to interact with.
OPERA detected 16,000 neutrinos that were launched at it over the last three years. Out of more than 100,000,000,000,000,000,000.
If OPERA were extended to be a light-year in length and were made out of solid lead, it would still interact with fewer than half of the neutrinos that passed through it.
The three types of neutrinos in the standard model are the lightest particles with a non-zero mass ever discovered. The upper limit on the mass of the heaviest neutrino is still more than 4 million times lighter than the electron, the next lightest particle.
Oxygen molecules at room temperature move at a mean speed of about 440 meters per second. Because they are so light, neutrinos at room temperature would move at speeds more than 80% the speed of light.
The coldest depths of intergalactic space are at temperatures of just 2.73 Kelvin, heated primarily by the leftover radiation from the Big Bang.
A neutrino at this temperature would still be moving at 7% the speed of light.
The coldest temperature ever achieved in a laboratory is about half of one nanoKelvin above absolute zero. Neutrinos at that speed would still move at nearly 300 m/s, or more than 20 times as fast as Usain Bolt at top speed.