X-ray: NASA/CXC/SAO; Optical: NASA/ESA/STScI/AURA;
IR:NASA/JPL/Caltech; Image Processing: NASA/CXC/SAO/N. Wolk
A group of dead stars known as “spider pulsars” are obliterating
companion stars within their reach. Data from NASA’s Chandra X-ray Observatory of the globular
cluster Omega
Centauri is helping astronomers understand how these spider pulsars prey on
their stellar companions.
A pulsar is the spinning dense core that remains after a
massive star collapses into itself to form a neutron
star. Rapidly
rotating neutron stars can produce beams of radiation. Like a rotating lighthouse beam, the radiation can
be observed as a powerful, pulsing source of radiation, or pulsar. Some pulsars
spin around dozens to hundreds of times per second, and these are known as
millisecond pulsars.
Spider pulsars are a special class
of millisecond pulsars, and get their name for the damage they inflict on small
companion stars in orbit around them. Through winds of energetic particles
streaming out from the spider pulsars, the outer layers of the pulsar’s
companion stars are methodically stripped away.
Astronomers recently discovered 18
millisecond pulsars in Omega Centauri — located about 17,700 light-years from
Earth — using the Parkes and MeerKAT radio telescopes. A pair of astronomers
from the University of Alberta in Canada then looked at Chandra data of Omega
Centauri to see if any of the millisecond pulsars give off X-rays.
They found 11 millisecond pulsars emitting X-rays, and five of those were spider pulsars concentrated near the center of Omega Centauri. The researchers next combined the data of Omega Centauri with Chandra observations of 26 spider pulsars in 12 other globular clusters.
A close-up image of Omega Centauri, in X-ray &
optical light, shows the locations of some of the spider pulsars. Spider
pulsars are a special class of millisecond pulsars, and get their name for the
damage they inflict on small companion stars in orbit around them.
X-ray: NASA/CXC/SAO; Optical: NASA/ESA/STScI/AURA;
Image Processing: NASA/CXC/SAO/N. Wolk
There are two varieties of spider pulsars based on the size of the star
being destroyed. “Redback” spider pulsars are damaging companion stars weighing
between a tenth and a half the mass of the Sun. Meanwhile, the “black widow”
spider pulsars are damaging companion stars with less than 5 percent of the
Sun’s mass.
The team found a clear difference
between the two classes of spider pulsars, with the redbacks being brighter in
X-rays than the black widows, confirming previous work. The team is the first
to show a general correlation between X-ray brightness and companion mass for
spider pulsars, with pulsars that produce more X-rays being paired with more
massive companions. This gives clear evidence that the mass of the companion to
spider pulsars influences the X-ray dose the star receives.
The X-rays detected by Chandra are
mainly thought to be generated when the winds of particles flowing away from
the pulsars collide with winds of matter blowing away from the companion stars
and produce shock
waves, similar to
those produced by supersonic aircraft.
Spider pulsars are typically
separated from their companions by only about one to 14 times the distance
between the Earth and Moon. This close proximity — cosmically speaking — causes
the energetic particles from the pulsars to be particularly damaging to their
companion stars.
This finding agrees with
theoretical models that scientists have developed. Because more massive stars
produce a denser wind of particles, there is a stronger shock — producing
brighter X-rays — when their wind collides with the particles from the pulsar.
The proximity of the companion stars to their pulsars means the X-rays can
cause significant damage to the stars, along with the pulsar’s wind.
Chandra’s sharp X-ray vision is
crucial for studying millisecond pulsars in globular clusters because they
often contain large numbers of X-ray sources in a small part of the sky, making
it difficult to distinguish sources from each other. Several of the millisecond
pulsars in Omega Centauri have other, unrelated X-ray sources only a few arc
seconds away. (One arc second is the apparent size of a penny seen at a
distance of 2.5 miles.)
The paper describing these results
will be published in the December issue of the Monthly Notices of the Royal
Astronomical Society, and a preprint of the accepted paper is available online. The authors of the paper are Jiaqi (Jake) Zhao and
Craig Heinke, both from the University of Alberta in Canada.
NASA’s Marshall Space Flight Center
manages the Chandra program. The Smithsonian Astrophysical Observatory’s
Chandra X-ray Center controls science operations from Cambridge, Massachusetts,
and flight operations from Burlington, Massachusetts.
Read
more from NASA’s Chandra X-ray Observatory.
For more Chandra images, multimedia and related materials, visit: https://www.nasa.gov/mission/chandra-x-ray-observatory/
Source: Chandra Catches Spider Pulsars Destroying Nearby Stars - NASA
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