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Chandra Catches Spider Pulsars Destroying Nearby Stars


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A cluster brimming with millions of stars glistens like an iridescent opal in this image from NASA's Spitzer Space Telescope. Called Omega Centauri, the sparkling orb of stars is like a miniature galaxy. It is the biggest and brightest of the 150 or so similar objects, called globular clusters, that orbit around the outside of our Milky Way galaxy. Stargazers at southern latitudes can spot the stellar gem with the naked eye in the constellation Centaurus. Globular clusters are some of the oldest objects in our universe. Their stars are over 12 billion years old, and, in most cases, formed all at once when the universe was just a toddler. Omega Centauri is unusual in that its stars are of different ages and possess varying levels of metals, or elements heavier than boron. Astronomers say this points to a different origin for Omega Centauri than other globular clusters: they think it might be the core of a dwarf galaxy that was ripped apart and absorbed by our Milky Way long ago. In this new view of Omega Centauri, Spitzer's infrared observations have been combined with visible-light data from the National Science Foundation's Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory in Chile. Visible-light data with a wavelength of .55 microns is colored blue, 3.6-micron infrared light captured by Spitzer's infrared array camera is colored green and 24-micron infrared light taken by Spitzer's multiband imaging photometer is colored red. Where green and red overlap, the color yellow appears. Thus, the yellow and red dots are stars revealed by Spitzer. These stars, called red giants, are more evolved, larger and dustier. The stars that appear blue were spotted in both visible and 3.6-micron-, or near-, infrared light. They are less evolved, like our own sun. Some of the red spots in the picture are distant galaxies beyond our own.
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.

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.
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/

News Media Contact

Megan Watzke
Chandra X-ray Center
Cambridge, Mass.
617-496-7998

Jonathan Deal
Marshall Space Flight Center
Huntsville, Ala.
256-544-0034

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