The Vela pulsar is a well-known gamma ray pulsar and is one of the brightest gamma ray sources. Data from the Chandra X-ray Observatory shows evidence of precession. It is the first neutron star observed to precess. The Fermi Large Area Telescope (LAT), which is in a 95-day orbit around Earth and scans the entire sky every three hours looking for gamma ray sources, observed and tracked Vela's position for 51 months and the images were used to make a movie showing Vela's position with time, which can be seen here: http://www.nasa.gov/mission_pages/GLAST/news/spirograph.html
The cause for precession is still unknown, but the Chandra scientists have two theories:1. It has been distorted, possibly by its fast rotation and interaction of its crust with the superfluid core, and is no longer a perfect sphere. Because of its density, even small distortions have a large effect.
2. The strong magnetic field is influencing the shape of the jet. According to the Chandra team, "if the jet develops a small bend caused, by precession, the magnetic field's lines on the inside of the bend will become more closely spaced. This pushes particles toward the outside of the bend, increasing the effect."
Some quick facts:
Vela is 12 miles in diameter.
It makes a complete rotation in 89 milliseconds.
The precession period is estimated at ~120 days.
References:
http://www.nasa.gov/mission_pages/GLAST/news/spirograph.htmlFrom Chandra X-Ray Observatory http://www.chandra.si.edu/press/13_releases/press_010713.html
small correction, the Fermi satellite is in a much closer orbit (95 minute period).
ReplyDeletebig correction. Fermi is not monitoring the motion of the Vela pulsar. It is using the Vela pulsar to monitor the spacecrafts motion.
3 points.