November 3, 2011
Scientists Discover Powerful Millisecond Pulsar
NASA said on Thursday that its scientists have discovered a surprisingly powerful millisecond pulsar that challenges existing theories.The international team of scientists used NASA's Fermi Gamma-ray Space Telescope to find that the object is the most luminous pulsar detected in the galaxy cluster to date, spinning at 11,000 rotations per minute.
The researchers wrote in the November 3 issue of the journal Science that the pulsar is only 25 million years old. Most millisecond pulsars are around a billion years old.
"We were very surprised to discover that the pulsar radiates very brightly in the gamma radiation band as well," Damien Parent from the US Center for Earth Observing and Space Research said in a press release. "We did not expect these millisecond pulsars to be so bright. This implies an unexpectedly strong magnetic field for such a rapidly rotating pulsar."
The object, PSR J1823-3021A, lies in NGC 6624, which is a spherical collection of ancient stars called a global cluster.
The cluster is about 10 billion years old and lies about 27,000 light-years away toward the constellation Sagittarius.
A pulsar is a type of neutron star that emits electromagnetic energy at periodic intervals. A neutron star holds half a million times more mass than Earth and is no larger than a city.
Millisecond pulsars are the fastest of pulsars, holding the record of 43,000 revolutions per minute.
Scientists believe millisecond pulsars can achieve these high speeds because they are gravitationally bound in binary systems with stars. The impact of gas over time eventually helps the pulsar spin.
The global cluster NGC 6624 was able to be detected by Fermi Lab's Large Area Telescope (LAT) due to its high output of gamma rays. These clusters normally do not emit enough of these gamma rays to be picked up by LAT.
"It's amazing that all of the gamma rays we see from this cluster are coming from a single object," Paulo Freire, the study's lead author, at the Max Planck Institute for Radio Astronomy in Bonn, Germany, said in a press release. "It must have formed recently based on how rapidly it's emitting energy. It's a bit like finding a screaming baby in a quiet retirement home."
The millisecond pulsar was previously identified as a pulsar by its radio emission, but none of the new pulsars detected by another team of scientists using Fermi data are millisecond pulsars. Only one pulsar of that data was able to emit radio waves.
"We have now discovered more than 100 of these objects with radio telescopes," Paulo Freire from the Max Planck Institute for Radio Astronomy said in a press release. "The high sensitivity of the Fermi telescope has now enabled us to track down a millisecond pulsar by its gamma radiation as well for the first time."
Image 1: This plot shows the positions of nine new pulsars (magenta) discovered by Fermi and of an unusual millisecond pulsar (green) that Fermi data reveal to be the youngest such object known. With this new batch of discoveries, Fermi has detected more than 100 pulsars in gamma rays. Credit: NASA/DOE/Fermi LAT Collaboration
Image 2: This image shows the on and off state of gamma rays from pulsar J1823-3021A as seen by Fermi's Large Area Telescope (LAT). The object pulses 183.8 times a second and has a spin period of 5.44 milliseconds, which translates to 11,000 rpm. Credit: NASA/DOE/Fermi LAT Collaboration
Image 3: To celebrate these achievements, the Fermi team has created an interactive feature on pulsars. Called the Fermi Pulsar Explorer, the interactive includes an all-sky map that links to information about each of the 101 Fermi pulsars known so far, as well as video and background information on Fermi and gamma-ray astronomy. [ View interactive ]
On the Net: