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Narrator: Parkes 1441+25 is a distant

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galaxy powered by a supermassive black hole. It's so far away

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its light takes more than half the current age of the universe to reach us.

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This is NASA's Fermi Gamma-ray Space Telescope,

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our sharpest satellite eyes on the gamma-ray sky. But Fermi's

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effective collecting area is about the size of two office desks. It can't

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catch everything. Ground-based gamma-ray observatories sport

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much larger light collectors than Fermi, but like traditional telescopes, they

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only work at night. Both MAGIC and VERITAS work

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by catching faint flashes of visible light produced when a high-energy

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gamma ray strikes the upper atmosphere. This creates a shower

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of fast-moving charged particles that emit a glow called Cerenkov radiation.

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On April 16, 2015,

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Parkes 1441 was exhibiting high activity across all wavelengths.

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Scientists looking at Fermi data reported a strong gamma-ray

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outburst. Based on this alert, scientists on the MAGIC team began

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monitoring the galaxy and detected very-high-energy gamma rays.

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That was the cue for VERITAS to take a look, and it also captured the

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quasar's very-high-energy emission.  These detections were

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remarkable because high-energy light usually can't travel extreme distances

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These gamma rays had been traveling for half the age of the cosmos

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passing through all the light emitted by stars, supernovae, and everything else

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that flashed and glowed across more than 7 billion years of cosmic history.

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Astronomers call this remnant glow is called the extragalactic background light

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background light. When a gamma ray strikes this lower-energy light, it converts into

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a pair of particles, an electron and a positron. The farther

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gamma rays travel the more likely it is they'll undergo this process, which effectively

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erases the gamma rays from the universe before we have the opportunity to detect

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them. Parkes 1441 is one of the most

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distant sources of gamma rays with energies above 100 GeV,

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tens of billions of times the energy in visible light. That the light

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reached us at all provides information about the extragalactic background light

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when the universe was half its present age. Those gamma rays

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originated from the particle jet produced by the galaxy's supermassive black hole.

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Astronomers think they started their journey only about 5 light-years from the

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black hole. Escaping the galaxy's crowded central regions

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means this high-energy light never interacted with matter or starlight, collisions

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that would have doomed them to convert into particles. This is one reason

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why extremely energetic gamma rays are few and far between, and why astronomers

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prize the relatively few photons they can find.

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The story of gamma rays from Parkes 1441 isn't a mere tale of survival.

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These photons executed a jailbreak of cosmic proportions,

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and it took Fermi, MAGIC, and VERTIAS to round them up.

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[Beeping]

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