The Fermi Gamma-ray Space Telescope only settled into its orbit a few months ago, but it’s already producing results that are delighting astronomers. Yesterday, NASA announced that Fermi had found a strange pulsar (a fast-spinning neutron star) by detecting only the gamma rays it emits. This is a first, NASA explains. Although astronomers have catalogued nearly 1800 pulsars, this is the first pulsar that seems to emit only gamma-ray radiation. Most other pulsars have been found using radio telescopes, although some also beam energy in visible light and X-rays [New Scientist].
Neutron stars are the small and incredibly dense bodies formed when massive stars explode into supernovas; perhaps the oddest of neutron stars are pulsars, which send out jets of radiation from their magnetic poles that sweep across Earth’s line of sight as the star spins on its axis. The newfound pulsar, which sits 4,600 light-years away in the constellation Cepheus, rotates at about a million miles an hour, and its beam of gamma rays reaches Earth about three times a second [National Geographic News]. Pulsars are often compared to lighthouses for the way their beams flash across our telescopes (see NASA animation).
The findings, published in Science [subscription required], suggest that astronomers may have to revise their estimates of the number of neutron stars in the galaxy, as there may be many more pulsars which have been invisible to older radio telescopes. “This is the first pulsar discovered only through gamma-ray pulses. This is an exciting result because it means that a lot of pulsars are hidden,” says Fermi science team member Alice Harding…. “Fermi is doing exactly what we expected it to do: find all these pulsars in gamma-rays that we don’t see in the radio,” adds radio astronomer Michael Kramer.
Further studies will investigate the heaps of questions left in the wake of this discovery, including why this pulsar doesn’t appear to emit the typical radio waves. Researchers will also investigate whether mysterious bursts of gamma rays previously detected by other telescopes are a result of unseen pulsars. The Fermi telescope has the rest of its five-year mission to attempt to solve these conundrums.
Bad Astronomy: Pulsar SMASH! has much more on this discovery
80beats: Brightest Gamma Ray Burst Ever Observed Was Aimed Straight at Earth
80beats: First Map of the “Gamma Ray Universe” Produced
80beats: Pulsars and Black Holes and Dark Matter, Oh My!