Fermi Captures Pulsar's Gamma-Ray Glow
New satellite reveals secrets of spinning cosmic beacons.
Scientists using NASA’s Fermi telescope have detected high-energy gamma-ray emissions from 55 pulsars, including many previously unknown and a surprising number of super-fast millisecond pulsars.
Before Fermi launched, only seven pulsars were known to shine in gamma-rays. Pulsars are like cosmic lighthouses, incredibly dense, rapidly spinning stars that spray beams of radiation across the galaxy. The Fermi Large Area Telescope (LAT) captures these powerful gamma-ray flashes, allowing scientists to peer into the extreme physics of these objects.
Unveiling Pulsar Emission Mechanisms
Researchers analyzed data from Fermi’s first year, specifically looking at how pulsars generate their powerful high-energy beams. They questioned whether these light beams come from:
- Near the magnetic poles, or
- Higher up in the pulsar's magnetic bubble (magnetosphere, the region around a star, planet, or other celestial object that is dominated by its magnetic field).
They also investigated if millisecond pulsars, which spin hundreds of times per second, also emit these super-energetic rays.
The team pointed Fermi at approximately 230 known pulsar locations. They also hunted for new, unseen pulsars within the gamma-ray data. "The sensitivity of the LAT allowed us to investigate the high-energy emission from pulsars with unprecedented detail," said a study author.
Using two methods – timing known pulsars with existing data and searching for new ones – they found a cosmic jackpot.
Electrifying Results
The results were electrifying. Fermi found gamma-ray pulses from:
- 22 normal pulsars
- 9 millisecond pulsars
This means these super-fast spinners share the same high-energy mechanisms as their slower cousins.
Most of these pulsars showed two sharp flashes per rotation, like a double beam. Their gamma-ray light typically cut off at energies below 10 gigaelectronvolts, a measure of energy. The study also found that brighter gamma-ray pulsars tend to be those that are losing more rotational energy, similar to how a spinning toy slows down over time.
These findings strongly support models suggesting that gamma-ray beams come from high up in the magnetosphere, away from the magnetic poles. It appears gamma-ray pulsars emit their light in wide, fan-like beams, separate from their radio waves.
Future Prospects
The scientists acknowledge some uncertainties, mainly in knowing the exact distances to these pulsars, which impacts how bright they appear. Future observations with more data from Fermi will help clarify these details and potentially reveal even more faint gamma-ray pulsars.
Fermi’s cosmic eye is just beginning to map the most extreme light sources in our universe.
Abdo, A. A., et al. "Pulsar observations with the Fermi LAT: what we have seen." arXiv preprint arXiv:0912.3666 (2009).