At the end of its life, all that may be left of a very large star is a tiny, super-heavy, tightly compacted rotating neutron star called a pulsar. To find its illusive signature, researchers draw on the Fermi Gamma-Ray Space Telescope’s Large Area instrument. Gamma rays are pure energy. When they smash into the detector’s tungsten plate, Einstein’s E=mc2 equation takes over, spawning a pair of subatomic particles; one electron and one anti-matter mirror image of that electron called a positron. Working back up the trails of these particles, astrophysicists derive a direction, pointing the way back to the source of the gamma ray on the sky. Meanwhile, Fermi’s calorimeter device absorbs the particles and measures their energy. By painstakingly calculating the location and power of each gamma ray hit, scientists use the FERMI data to build a picture of the object that emitted them. It takes a ferocious amount of computing power to work out – by sheer trial and error – the true position of the source. Pulsars can spin many times each second, spraying tight streams of radio waves and gamma radiation across the Universe. These strange objects really are like light houses; if a civilization in one part of the galaxy wanted to reveal it’s location to another society far way, it might simply broadcast it’s distance to three pulsars, marked by the blip-rate of their cosmic beacons.
The large area detector (LAT) onboard the Fermi Gamma-Ray Space Telescope records the arrival times and direction of gamma photons. By analyzing this data, scientists can pinpoint these rotating neutron stars through photon count patterns.
Credit: SPACE.com / NASA / GSFC / Fermi / Cruz de Wilde /AEI