In 2017, NASA's Fermi Gamma-ray Space Telescope connected
gamma rays, the highest-energy form of light, with new
cosmic messengers--gravitational waves and high-energy neutrinos.
For the first time, the discoveries linked these new signals to
the one sky watchers have known for millennia -- light.
First, gravitational waves and gamma rays were emitted from merging neutron
stars. Fermi saw the first-ever light detected from
a gravitational wave event. Then, just weeks later, Fermi
connected a high-energy neutrino seen by the IceCube experiment at the
South Pole to a black-hole-powered galaxy, which fires a jet of matter
that emits both neutrinos and gamma rays. This is no
overnight success story. The origins of both these breakthroughs
span more than a century. As the
19th century closed, scientists worked to understand many new phenomena
including radioactivity, and new forms of light --
X-rays and gamma rays. Light was expected to need a medium, called
the "aether," in order to move through space, which meant its speed should change when measured
in different directions on the moving Earth. Yet no changes were seen.
Solving this puzzle led to Einstein's special theory
of relativity, which assumed light in a vacuum moves at a constant speed that
nothing can exceed. His theory formed a theoretical basis for
particle physics... ...which in 1912 incorporated an unexpected
source -- a rain of particles from space called cosmic rays.
Einstein's general theory of relativity, his theory
of gravity, regarded space-time as the fabric of the cosmos.
Space-time tells matter how to move, and matter tells space-time how to
curve. As scientists probed the subatomic
realm, one type of radioactive decay suggested the presence
of a new lightweight particle, dubbed the "neutrino."
Later, Einstein and Nathan Rosen showed
that accelerating masses can create gravitational waves that ripple
across space-time.
Following World War II, technological advances permitted new kinds
of observations. In the mid-Fifties, neutrinos were detected for the
first time. Richard Feynman showed that gravitational waves must
move matter, which means they're detectable. In a few years, the first
efforts to do so began. The 1960s brought
the first gamma rays seen in space, the first neutrinos
detected from the Sun's interior, and something new -- later called
gamma-ray bursts, or GRBs -- was caught by satellites looking for banned
tests of nuclear weapons. In 1971,
Rainer Weiss conceived of a way to detect gravitational waves
using lasers, one of the roots of LIGO.
1987 delivered the brightest supernova in nearly 400
years. Three experiments caught neutrinos from the star's collapse.
Instruments on balloons saw gamma rays from radioactive elements
in the explosion's debris. The 1990s
and 2000s brought: new satellites for exploring the
gamma-ray universe; the construction and first operation of LIGO;
and AMANDA, a neutrino detector built under the ice at the South Pole.
In 2005,
NASA's Swift satellite showed that short gamma-ray bursts likely come
from merging neutron stars. Soon after,
NASA launched Fermi, providing our best-ever view of the gamma-ray sky.
AMANDA morphed into IceCube, which was completed in 2010.
It monitors a cubic kilometer of ice under the South Pole
for neutrinos. The same year, LIGO shut down
for years of upgrades. IceCube reported more than
two dozen high-energy neutrinos -- likely arrivals from
beyond our galaxy. In 2015, the upgraded LIGO
saw the first gravitational waves. The source: merging black holes
over a billion light-years away. And in 2017,
gamma-ray counterparts accompanied both a gravitational wave
event and a cosmic neutrino source.
Multimessenger astronomy -- and its promise of greater insight into the most
powerful processes in the universe -- has arrived.
[Music]
[NASA Astrophysics]
[Beeping]