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B1957+20 (Black Widow Pulsar):
A Cocoon Found Inside the Black Widow's Web
This composite X-ray (red/white) and optical (green/blue) image reveals an elongated cloud, or cocoon, of high-energy particles flowing behind
the rapidly rotating pulsar, B1957+20 (white point-like source). The
pulsar, a.k.a. the "Black Widow" pulsar, is moving through the galaxy at
a speed of almost a million kilometers per hour. A bow shock wave due to
this motion is visible to optical telescopes, shown in this image as the
greenish crescent shape. The pressure behind the bow shock creates a second shock wave that sweeps the cloud of high-energy particles back from the pulsar to form the cocoon.
The Black Widow pulsar is emitting intense high-energy radiation that
appears to be destroying a companion star through evaporation. It is one
of a class of extremely rapid rotating neutron stars called millisecond
pulsars.
These objects are thought to be very old neutron stars that have been
spun up to rapid rotation rates with millisecond periods by pulling
material off their companions. The steady push of the infalling matter
on the neutron star spins it up in much the same way as pushing on a
merry-go-round causes it to rotate faster.
The advanced age, very rapid rotation rate, and relatively low magnetic
field of millisecond pulsars put them in a separate class from young
pulsars, such as the Crab Nebula. Yet the Chandra data show that this
billion-year-old rejuvenated pulsar is an extremely efficient generator
of matter and antimatter particles, just like its younger cousins.
The key is the rapid rotation of B1957+20. The Chandra result confirms
the theory that even a relatively weakly magnetized neutron star can
generate intense electromagnetic forces and accelerate particles to high
energies to create a pulsar wind, if it is rotating rapidly enough.
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Fast Facts for
B1957+20 (Black Widow Pulsar):
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Credit
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X-ray: NASA/CXC/ASTRON/B.Stappers et al.; Optical: AAO/J.Bland-Hawthorn & H.Jones
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Scale
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Image is 1.2 arcmin per side
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Category
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Neutron Stars/X-ray Binaries
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Coordinates
(J2000)
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RA 19h 59m 36.80s | Dec +20º 48' 15.10"
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Constellation
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Sagitta
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Observation
Date
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June 21, 2001
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Observation
Time
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12 hours
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Obs.
ID
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1911
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Color
Code
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Energy (X-ray = red & white; Optical = blue & green;)
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Instrument
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ACIS
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Distance
Estimate
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5,000 light years
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Release Date
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February 27, 2003
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