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  • Just now, somewhere in the universe, a star exploded.

  • There goes another one.

  • In fact, a supernova occurs every second or so in the observable universe,

  • and there is one on average every 25 to 50 years

  • in a galaxy the size and age of the Milky Way.

  • Yet we've never actually been able to watch one happen

  • from its first violent moments.

  • Of course, how would we?

  • There are hundreds of billions of stars close enough

  • that we could watch the supernova explosion

  • break through the surface of the star.

  • But we'd have to have our best telescopes focused on the right one

  • at precisely the right time to get meaningful data.

  • Suffice it to say, the odds of that happening are astronomically low.

  • But what if we could anticipate a supernova before its light reached us?

  • That may seem impossible.

  • After all, nothing travels faster than the speed of light, right?

  • As far as we know, yes.

  • But in a race, fast doesn't matter if you take a detour

  • while someone else beelines it for the finish line.

  • For exactly that reason,

  • photons don't win the supernova race to Earth.

  • Neutrinos do.

  • Here's why.

  • There are two types of supernova.

  • Type 1 is when a star accumulates so much matter from a neighboring star,

  • that a runaway nuclear reaction ignites and causes it to explode.

  • In type 2, the star runs out of nuclear fuel,

  • so the gravitational forces pulling in

  • overwhelm the quantum mechanical forces pushing out,

  • and the stellar core collapses under its own weight in a hundredth of a second.

  • While the outer reaches of the star are unaffected by the collapsed core,

  • the inner edges accelerate through the void,

  • smash into the core, and rebound to launch the explosion.

  • In both of these scenarios,

  • the star expels an unparalleled amount of energy,

  • as well as a great deal of matter.

  • In fact, all atoms heavier than nickel, including elements like gold and silver,

  • only form in supernova reactions.

  • In type 2 supernovae,

  • about 1% of the energy consists of photons,

  • which we know of as light,

  • while 99% radiates out as neutrinos,

  • the elementary particles that are known for rarely interacting with anything.

  • Starting from the center of the star,

  • the exploding matter takes tens of minutes, or even hours,

  • or in rare cases, several days, to reach and break through the surface of the star.

  • However, the neutrinos, thanks to their non-interactivity,

  • take a much more direct route.

  • By the time there is any visible change in the star's surface,

  • the neutrinos typically have a several hour head start over the photons.

  • That's why astronomers and physicists

  • have been able to set up a project called SNEWS,

  • the Supernova Early Warning System.

  • When detectors around the world pick up bursts of neutrinos,

  • they send messages to a central computer in New York.

  • If multiple detectors receive similar signals within ten seconds,

  • SNEWS will trigger an alert warning that a supernova is imminent.

  • Aided by some distance and direction information from the neutrino detectors,

  • the amateur astronomers and scientists alike

  • will scan the skies and share information

  • to quickly identify the new galactic supernova

  • and turn the world's major telescopes in that direction.

  • The last supernova that sent detectable neutrinos to Earth was in 1987

  • on the edge of the Tarantula Nebula

  • in the large Magellanic Cloud, a nearby galaxy.

  • Its neutrinos reached Earth about three hours ahead of the visible light.

  • We're due for another one any day now, and when that happens,

  • SNEWS should give you the opportunity to be among the first to witness something

  • that no human has ever seen before.

Just now, somewhere in the universe, a star exploded.

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B2 TED-Ed supernova star core matter surface

【TED-Ed】How to detect a supernova - Samantha Kuula

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    SylviaQQ posted on 2015/09/08
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