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[Music throughout]

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NASA's Fermi Gamma-ray Space Telescope

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watches the sky for gamma
rays, the highest-energy form of light.

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These detections
help scientists learn more

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about the most powerful events
in the cosmos.

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However, a recent absence of gamma ray
detection

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may have been just as informative.

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Cosmic rays are small particles,
like protons

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and helium nuclei, traveling at nearly
the speed of light.

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It takes a lot of energy to accelerate
them to that speed,

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so scientists assume they're driven by powerful events

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like exploding stars called supernovae.

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Because cosmic rays are charged particles,

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they interact with magnetic fields as they travel.

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These interactions mean they don't follow
a straight line from their sources,

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and so scientists can't trace where they came from.

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But when cosmic rays smash into other particles,
they produce gamma rays.

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And gamma rays do travel to us
straight from their sources.

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Fermi has even detected such gamma rays
from supernova remnants,

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which are thousands of years old.

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If supernovae and their remnants
really are a key source of cosmic rays,

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then calculations tell astronomers how many
gamma rays Fermi should detect.

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But so far, the telescope hasn't

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seen enough gamma rays from these sources.

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Scientists had suspected this was because
supernovae were too far away,

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or observations began too late,
well after peak production.

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In May 2023, Fermi observed the most luminous nearby

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supernova seen since the mission launched
15 years ago.

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It captured data from the first few weeks

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of the explosion,

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when scientists anticipated

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the greatest production of cosmic rays.

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But Fermi didn't see any gamma rays

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from the explosion.

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Scientists aren't yet sure what this means

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for the link between cosmic rays and supernovae.

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There's still a lot of work left to do.

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But Fermi's non-detection has added a
very important new piece

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to this high-energy puzzle.

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[Music fades]

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NASA