By Jonny Lupsha, Wondrium Staff Writer
A newly detected gamma-ray burst could be the biggest ever. Scientists say that even at a distance of 2.4 billion light-years, it’s closer than most. Gamma-ray bursts were discovered in the 1960s.
Gamma-ray bursts (GRB) are the strongest and brightest explosions in the universe. Though much about them is still unknown, they’re believed to be generated during the formation of black holes. One such GRB was recently detected by several observatories on October 9 and may be the most energetic ever recorded. At an unusually close distance of 2.4 billion light-years from Earth, scientists first mistook it for a series of X-ray flashes from a much closer source.
GRBs were first detected in the 1960s by accident. In his video series Understanding the Universe: An Introduction to Astronomy, 2nd Edition, Dr. Alex Filippenko, Professor of Astronomy at the University of California, Berkeley, dives into the rich history of gamma-ray bursts.
A Recently Discovered Phenomenon
“The history of gamma-ray bursts—of celestial ones—starts in the late 1960s, when several spy satellites—called the Vela spy satellites—were launched by the U.S. Air Force to monitor Soviet compliance with the Nuclear Test Ban Treaty,” Dr. Filippenko said. “They wanted to see whether the Soviets were essentially exploding nuclear weapons, which create bursts of gamma rays in the process.”
The U.S. didn’t find any violations of the treaty but they found gamma-ray bursts taking place in outer space, lasting from a few seconds up to several hundred seconds each. The discovery was responsible for the birth of an entirely new branch of astrophysics.
“There are two main types of GRBs: the so-called long-duration and short-duration GRBs,” Dr. Filippenko said. “The long-duration GRBs […] don’t last long on a cosmic scale, just a few tens of seconds or a few hundred seconds, but that’s long compared to another class, the short-duration ones, which last only a second or two, or less.”
For a long time, nobody knew exactly what gamma-ray bursts were. According to Dr. Filippenko, between 1973 and 1992, 118 distinct hypotheses about their nature were published by theoretical astrophysicists. Some thought they were collisions of matter and anti-matter; others said they were comets striking neutron stars. Even Stephen Hawking incorrectly believed that they were miniature black holes exploding.
In 1996, a Breakthrough
For years, scientists used devices at major observatories to find some kind of counterpart to the gamma-ray bursts in order to study them or even pinpoint where they were occurring.
“In 1996, a huge breakthrough occurred when an X-ray satellite known as BeppoSAX was launched,” Dr. Filippenko said. “It had the capability of not only detecting gamma-ray bursts, but also of getting an image of that part of the sky where the burst occurred at lower photon energies: X-ray energies, rather than just the high-energy gamma rays.”
As BeppoSAX pinpointed the locations of gamma-ray bursts, scientists saw their X-ray counterparts and were able to search for fading optical afterglows. Using those, they were able to determine that GRBs were, in fact, coming from billions of light-years away. Continued study gave scientists a huge piece of the puzzle.
Evidence showed that the radiation coming from GRBs came out in jets, in a highly beamed fashion, like lasers. For some reason, relativistic particles—particles traveling at nearly the speed of light—get ejected along two axes, interact with material and cause a large amount of radiation to come out.
“There’s some engine here, which might be very small, creating a burst of energetic particles, which hit each other—there are many such bursts—causing internal shocks because these various bursts of particles slam into each other,” Dr. Filippenko said. “The collisions produce a lot of gamma rays; that’s the gamma-ray burst.
“Then some time later, those energetic clumps of particles hit clouds of gas, the interstellar medium, and those collisions produce radio waves, and optical radiation, and X-rays.”
The internal shock produces gamma rays while the external shock produces the afterglow at other wavelengths.
Understanding the Universe: An Introduction to Astronomy, 2nd Edition, is now available to stream on Wondrium.