NASA’s Fermi Gamma Ray Space Telescope spent a year collecting data from a thousand gamma ray sources and came up with this, the best map to date of the extreme universe. It also gave Einstein a shot in the arm by confirming the scientist’s theories of space-time.
Gamma rays represent the highest-energy form of light in the universe, and often emerge from sources such as massive black holes that spew out fast jets of matter. One particular event known as a short gamma ray burst confirmed Einstein’s view that radio waves, infrared, visible light, X-rays and gamma rays all travel at the same speed through space.
Scientists have explored a theory that space-time represents a frothy, dynamic structure at incredibly tiny physical scales trillions of times smaller than electrons. Models have predicted that the foamy space-time could cause higher-energy gamma rays to move more slowly than lower energy photons — a prediction put to the test by the space telescope’s observations.
“Physicists would like to replace Einstein’s vision of gravity — as expressed in his relativity theories — with something that handles all fundamental forces,” said Peter Michelson, a scientist working on Fermi’s Large Area Telescope, or LAT, at Stanford University in California. “There are many ideas, but few ways to test them.”
Fermi detected the GRB 090510 event on May 10, and astronomers deduced that the gamma ray burst likely came from the collision of two neutron stars 7.3 billion light-years away. Two gamma ray photons in particular had wildly different levels of energy millions of times apart. And yet the pair arrived at Fermi’s detectors just nine-tenths of a second apart after traveling across seven billion years.
“This measurement eliminates any approach to a new theory of gravity that predicts a strong energy dependent change in the speed of light,” Michelson said.
The thousand gamma ray sources discovered by Fermi mark a fivefold increase in the number previously known, and a few have proved particularly record-breaking. For instance, the GRB 090510 event ejected its matter at 99.99995 percent of light speed. The highest energy seen in a gamma ray yet came from GRB 090902B in the form of 33.4 billion electron volts — about 13 billion times the energy of visible light.
A third source, GRB 080916C, created enough total energy to rival 9,000 supernova explosions. And if that’s not crazy enough, consider that gamma ray bursts also serve as a good source of those ghostly neutrinos.