NASA’s Fermi Gamma Ray Space Telescope recently discovered a previously unknown pulsar. This is an exceptional discovery since this pulsar is emitting only gamma rays, and displays no radio emissions that all known pulsars emit. This discovery is another example of Fermi’s capabilities, and also suggests there is a new class of pulsars waiting to be detected and understood.
Pulsars are highly magnetized neutron stars rotating thousands of times an hour and emitting a beam of electromagnetic radiation in the form of radio waves. We observe this radiation only when the beam is pointing towards the Earth, thus creating the pulsing nature that gives pulsars their name. The first pulsar was observed in 1967 by student radio astronomer Jocelyn Bell Burnell and her thesis advisor Antony Hewish, who later received a Nobel Prize for his role in the discovery of pulsars. Surprised by the regularity of its emissions, they dubbed their discovery LGM-1, for Little Green Men, a name for extraterrestrial intelligent beings.
Since the initial discovery, some 1,800 pulsars have been discovered. They are usually detected through their radio emissions. However, some pulsars, in addition to their radio emissions, emit pulses in the visible light, x-ray and even gamma ray wavelengths. NASA’s Fermi Gamma Ray Space Telescope recently detected a pulsar sending a beam of radiation in the direction of Earth about three times every second.
This beam consists solely of gamma rays, setting this pulsar apart from all previously detected pulsars. It is inactive in the parts of the electromagnetic spectrum where pulsars are usually found. This points to the possibility of there being a new type of pulsar waiting to be discovered and studied. “This is the first example of a new class of pulsars,” says Stanford University‘s Peter Michelson, principal investigator for Fermi’s Large Area Telescope. “[We think] it will give us fundamental insights into how these collapsed stars work.”
The recently discovered pulsar lies in the remains of a supernova that exploded 10,000 years ago, called CTA 1, in the constellation Cepheus, approximately 4,600 light years away. The pulsar is emitting an amount of energy that is one thousand times greater than the sun’s energy.
This discovery is a good example of Fermi’s capabilities. “The Large Area Telescope provides us with a unique probe of the galaxy’s pulsar population, revealing objects we would not otherwise even know exist,” says Fermi project scientist Steve Ritz of the Goddard Space Flight Center. Fermi’s Large Area Telescope scans the entire sky every three hours and detects photons with energies ranging from 20 million to more than 300 billion times the energy of visible light. “This observation shows the power of the Large Area Telescope,” Michelson adds. “It is so sensitive that we can now discover new types of objects just by observing their gamma-ray emissions.”
Shalhevet is finishing her B.A. degree in physics and mathematics at the Hebrew University in Jerusalem. She will begin her M.A. studies in physics next year and will focus on cosmology and astrophysics, her main topics of interest.