Fermi Space Telescope

An international team of scientists using NASA's Fermi Gamma-ray Space Telescope has discovered a surprisingly powerful millisecond pulsar that challenges existing theories about how these objects form. At the same time, another team has exploited improved analytical techniques to locate nine new gamma-ray pulsars in Fermi data. A pulsar, also called a neutron star, is the closest thing to a black hole astronomers can observe directly, crushing half a million times more mass than Earth into a sphere no larger than a city. This matter is so compressed that even a teaspoonful weighs as much as Mount Everest. Typically, millisecond pulsars are a billion years or more old, ages commensurate with a stellar lifetime. But in the Nov. 3 issue of Science, the Fermi team reveals a bright, energetic millisecond pulsar only 25 million years old. The object, named PSR J1823--3021A, lies within NGC 6624, a spherical assemblage of ancient stars called a globular cluster, one of about 160 similar objects that orbit our galaxy. The cluster is about 10 billion years old and lies about 27,000 light-years away toward the constellation Sagittarius.
The animation illustrates how analysis of Fermi data reveals new pulsars. Fermi's LAT records the precise arrival time and approximate direction of the gamma rays it detects, but to identify a pulsar requires additional information -- its position in the sky, its rotation period, and the rate at which the pulsar's rotation is slowing. The pulsars are so far away that even Fermi's sensitive LAT detects very few gamma rays from these objects -- as few as a single photon per 100,000 rotations. The Hannover team used new methods to carry out a so-called blind search, using computers to check many different combinations of position and rotational behavior, to see if these matched with the arrival times of the Fermi LAT photons coming from near this direction. The search used the 8,000 photons deemed most probable to come from a pulsar at the putative position, which Fermi's LAT had collected during its three years in orbit. When the photon arrival times match up with the putative pulsar position and rotation model, a regular pattern of peaks appears in the gamma-ray photon counts, as a function of the rotational position of the pulsar, and a new gamma-ray pulsar has been discovered.

Category:

Science & Technology

Tags:

• satellite
• GLAST
• gamma-ray
• universe