Monday, October 25, 2021

G11.2-0.3, a circularly symmetric supernova remnant containing a dense, rotating dead star at its center

When a massive star collapses, the outer layers of the star are destroyed in an extremely energetic explosion. Depending on the mass of the original star, a dense object, such as a neutron star or black hole, can form and fall behind at the center of the explosion. Such a neutron star, known as a "pulsar" when spinning rapidly, can be kicked out by the thermonuclear shock wave created when the star exploded, causing it to race through space at millions of miles per hour.

By combining X-ray and radio observations, astronomers have evidence that G11.2-0.3 is likely the result of the explosive death of such a massive star, perhaps witnessed in AD 386. Radio observations measure the rate of expansion of the remnant, which, in turn, can be used to calculate how long ago the star exploded. The radio data is consistent with the supernova remnant's association with the "guest star" reported by Chinese astronomers nearly 2,000 years ago. Chandra's ability to locate the pulsar almost in the center of G11.2-0.3 also supports the idea that this debris field could have been created around the time of Chinese observations. Surprisingly, the age of the pulsar determined from radio and X-ray data differs from the standard estimate of the age of the pulsar, usually determined by how fast it rotates. In this case, the so-called turning parameters suggest that the G11.2-0.3 is 10 times greater than the remaining age. This strongly argues that the spin ages of young pulsars can be very misleading and should be viewed with caution.

In the X-ray image of Chandra, the pulsar and a cigar-shaped cloud of energetic particles, known as the pulsar wind nebula, are predominantly seen as high-energy X-rays (blue). A layer of hot gas from the outer layers of the exploded star surrounds the pulsar and the pulsar's wind nebula and emits lower-energy X-rays (depicted in green and red).

NASA, Chandra, 1/30/07) by NASA's Marshall Space Flight Center

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