[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]