Astronomers using the Fermi Gamma-ray Space Telescope have found a surprisingly young, powerful and luminous millisecond pulsar. Over the past three years, Fermi has detected more than 100 gamma-ray pulsars and typically the ages of these objects are at least a billion year old. But this new object is just a youngster, born only about 25 million years ago.
“It is a bit like finding Justin Bieber when you thought you were at a Rolling Stones concert,” said Victoria Kaspi, physics professor, McGill University in Montreal, during a teleconference about two new discoveries made with the Fermi telescope. “Fermi has represented a huge leap forward in finding things that couldn’t have been imagined 25 years ago.”
In addition to the very young and bright pulsar, researchers announced they have also discovered a set of nine previously unknown gamma-ray pulsars, a new type that have extremely low luminosity. These were uncovered with a new technique to more efficiently sift through Fermi data.
The young millisecond pulsar, named PSR J1823?3021A was found within the globular cluster NGC 6624, not far from the center of our galaxy. Fermi has detected pulsars in globular clusters before, but usually what it finds are the combined gamma rays from many ancient pulsars within the clusters. But this time, surprisingly, the gamma rays originated from just one very powerful millisecond pulsar.
“At first we thought it was perhaps one hundred millisecond pulsars, but now we see it is just one,” said Paulo Freire, from the Max Planck Institute for Radio Astronomy in Bonn, Germany, also speaking to reporters during the teleconference. Freire is the lead author on a new paper published in the Astrophysical Journal. “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. This was a rather surprising discovery for everyone involved.”
A pulsar is a type of neutron star that emits electromagnetic energy at periodic intervals, sending out signals almost like a lighthouse. Pulsars that combine incredible density with extreme rotation are called millisecond pulsars. These millisecond pulsars are especially fascinating, as they are city-sized spheres about half millions times Earth’s mass, spinning at up to 43,000 revolutions per minute.
Millisecond pulsars are thought to achieve such speeds because they are gravitationally bound in binary systems with normal stars. During part of their stellar lives, gas flows from the normal star to the pulsar. Over time, the impact of this falling gas gradually spins up the pulsar’s rotation.
The nine new low luminosity pulsars found with Fermi emit less gamma radiation than those previously known and rotate only between three and twelve times per second. Only one of these pulsars was later also found to emit radio waves. Without the new technique, astronomers wouldn’t have found this faint pulsars.
““We used a new kind of hierarchical algorithm which we had originally developed for the search for gravitational waves, and we were quickly rewarded,” said Bruce Allen, director of the Max Planck Institute for Gravitational Physics, a co-author on the recent discoveries.
Using what is called a blind search, computers check many different combinations of position and rotational behavior, to see if they match the arrival times of photons hitting the Fermi Large Area Telescope (LAT) coming from the same direction. The search used the 8,000 photons deemed most probable to come from a pulsar at the recognized 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.
“It is a little like sifting through a pile of sand looking for diamonds,” Allen said, adding that the search is ongoing and they hope to find more.
Additionally, Allen said, users of the Einstein@Home project can now be part of this search, to help specifically to search for the first pure gamma-ray millisecond-pulsar. Allen is the director of this project and said this discovery would be a significant contribution to our understanding of pulsars.
NASA has a new interactive web feature about Fermi and the 100 pulsars it has now found.