mei 232013

May 23, 2013

PSR B1509-58, a pulsar in Circinus


Image Credit: NASA/CXC/SAO/P.Slane, et al.

PSR B1509-58 (B1509 for short) is a 1700 years old pulsar that lies about 17,000 light-years away from Earth in the southern constellation of Circinus (the Compass). It is surrounded by an X-ray nebula that spans about 150 light-years, and is associated with the supernova remnant 320.4-1.2.

After some supernova explosions, when a massive star – more than 8 and less than about 20 solar masses – collapses and becomes so dense that protons and electrons squish together to form neutrons, there remains a small, ultra-dense neutron star. (Above this mass, the remnant collapses to form a black hole.)

Rapidly rotating, highly magnetized neutron stars are called pulsars. The explosion throws a large cloud of dust and hot gas into space surrounding the neutron star. When this slams into the interstellar medium, it heats up so much it glows in X-rays.

Responsible for this remarkable pulsar wind nebula is the small, blueish-white pulsar in the center. This pulsar, B1509, is only twelve miles (less than 20 kilometers) in diameter, and rotates at a blazing speed of seven times per second. It is spewing a wind of charged particles out into the space around it at a prodigious rate, presumably because it has an intense magnetic field at its surface, estimated to be 15 trillion times stronger than the Earth’s magnetic field.

The combination of rapid rotation and ultra-strong magnetic field makes B1509 one of the most powerful electromagnetic generators in our Milky Way galaxy. This generator drives the energetic wind of electrons and ions away from the neutron star. As the electrons move through the magnetized nebula, they radiate away their energy and create the complex and intriguing structure that resembles a large cosmic hand.

In the innermost regions, a faint circle surrounds the pulsar, and marks the spot where the wind is rapidly decelerated by the slowly expanding nebula. Finger-like structures extend to the north, apparently energizing knots of material in a neighboring gas cloud known as RCW 89. The transfer of energy from the wind to these knots makes them glow brightly in X-rays (orange and red features to the upper right).

The temperature in this region appears to vary in a circular pattern around this ring of emission, suggesting that the pulsar may be precessing like a spinning top and sweeping an energizing beam around the gas in RCW 89.

The data for this image, taken with Chandra’s X-ray Observatory, were obtained in a total of 52 hours between 12/28/2004 and 10/18/2005. The lowest energy X-rays that Chandra detects are red, the medium range is green, and the most energetic ones are colored blue.

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