Transcripts of PKS_1441_captions

[Music] [Music] [Music] [Music] Narrator: Parkes 1441+25 is a distant galaxy powered by a supermassive black hole. It's so far away its light takes more than half the current age of the universe to reach us. This is NASA's Fermi Gamma-ray Space Telescope, our sharpest satellite eyes on the gamma-ray sky. But Fermi's effective collecting area is about the size of two office desks. It can't catch everything. Ground-based gamma-ray observatories sport much larger light collectors than Fermi, but like traditional telescopes, they only work at night. Both MAGIC and VERITAS work by catching faint flashes of visible light produced when a high-energy gamma ray strikes the upper atmosphere. This creates a shower of fast-moving charged particles that emit a glow called Cerenkov radiation. On April 16, 2015, Parkes 1441 was exhibiting high activity across all wavelengths. Scientists looking at Fermi data reported a strong gamma-ray outburst. Based on this alert, scientists on the MAGIC team began monitoring the galaxy and detected very-high-energy gamma rays. That was the cue for VERITAS to take a look, and it also captured the quasar's very-high-energy emission. These detections were remarkable because high-energy light usually can't travel extreme distances These gamma rays had been traveling for half the age of the cosmos passing through all the light emitted by stars, supernovae, and everything else that flashed and glowed across more than 7 billion years of cosmic history. Astronomers call this remnant glow is called the extragalactic background light background light. When a gamma ray strikes this lower-energy light, it converts into a pair of particles, an electron and a positron. The farther gamma rays travel the more likely it is they'll undergo this process, which effectively erases the gamma rays from the universe before we have the opportunity to detect them. Parkes 1441 is one of the most distant sources of gamma rays with energies above 100 GeV, tens of billions of times the energy in visible light. That the light reached us at all provides information about the extragalactic background light when the universe was half its present age. Those gamma rays originated from the particle jet produced by the galaxy's supermassive black hole. Astronomers think they started their journey only about 5 light-years from the black hole. Escaping the galaxy's crowded central regions means this high-energy light never interacted with matter or starlight, collisions that would have doomed them to convert into particles. This is one reason why extremely energetic gamma rays are few and far between, and why astronomers prize the relatively few photons they can find. The story of gamma rays from Parkes 1441 isn't a mere tale of survival. These photons executed a jailbreak of cosmic proportions, and it took Fermi, MAGIC, and VERTIAS to round them up. [Beeping] [Beeping] [Beeping]