2003 SPACE SCIENCE VIDEOTAPES |
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Tape Title | Record ID | Date Produced | TRT: |
Synopsis |
| EINSTEIN'S GRAVITATIONAL WAVES MAY SET SPEED LIMIT FOR PULSAR SPIN | G03-044 | 07/02/03 | 00:04:00 | Scientists have identified a cosmic speed limit for millisecond pulsars, the fastest-spinning objects in the Universe, based on observations of eleven nuclear-powered pulsars whipping about at nearly 20 percent the speed of light.
A group led by Prof. Deepto Chakrabarty of the Massachusetts Institute of Technology analyzed data on eleven millisecond pulsars from the Rossi X-Ray Timing Explorer (RXTE) spacecraft. Based on a statistical analysis, Chakrabarty and his colleagues deduced that the maximum pulsar spin rate seen in nature is below 760 revolutions per second and concluded that something acts to prevent pulsars from being spun up to even faster rates. Their article appears in the July 3, 2003 issue of the journal Nature. Their work supports a theory proposed by Prof. Lars Bildsten, of the University of California, Santa Barbara that gravitational radiation - ripples in the fabric of space predicted by Albert Einstein - can limit pulsar spins.
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TAPE CONTENTS: |
| ITEM (1): Accretion Spins Pulsar to Millisecond Range - When a pulsar is created in a supernova explosion, it is born spinning, but slows down over millions of years. Yet if the pulsar -- a dense star with strong gravitational attraction -- is in a binary system, then it can pull in, or accrete, material from its companion star. This influx of material can eventually spin up the pulsar to the millisecond range, rotating hundreds of revolutions per second.
Courtesy: NASA
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| ITEM (2): Nuclear Explosions on Pulsar Surface Help Scientists Determine Spin Rate - Material accumulating on the pulsar surface can sometimes
ignite, causing thermonuclear flashes that emit bursts of X-ray light. These thermonuclear flames spread across the surface of the pulsar in a few seconds. The team established that "burst oscillations", a kind of flickering, during these X-ray bursts provide a direct measure of the pulsar's spin rate. Thus, these bright bursts can be used to determine pulsar spin rates throughout the galaxy. This animation is a slow-motion depiction of a thermonuclear flash or X-ray burst spreading across a rotating pulsar. The pulsar would actually be rotating hundreds of revolutions per second.
Courtesy: NASA
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| ITEM (3): Emitted Gravitational Radiation Halts Pulsar's Spin Up - As the pulsar picks up speed through accretion, it becomes distorted from a perfect sphere due to subtle changes in the crust, depicted here by an equatorial bulge. Such slight distortion is enough to produce gravitational waves. Material flowing onto the pulsar surface from its companion star tends to quicken the spin, but loss of energy released as gravitational radiation tends to slow the spin due to the principle of conservation of energy. This competition may reach an equilibrium, setting a natural speed limit for millisecond pulsars beyond which they cannot be spun up.
Courtesy: NASA
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| ITEM (4): Rossi X-ray Timing Explorer Animation - The Rossi X-ray Timing Explorer (RXTE) was launched on December 30, 1995 from NASA's Kennedy Space Center. The mission is managed and controlled by NASA's Goddard Space Flight Center (GSFC) in Greenbelt, Maryland. Originally designed for a mission lifetime of two years with a goal of five, RXTE has passed that goal and is still performing well.
RXTE features unprecedented time resolution in combination with moderate spectral resolution to explore the variability of X-ray sources. Time scales from microseconds to months are covered in an instantaneous spectral range from 2 to 250 keV. This allows RXTE to detect pulsars with spin rates over 2,000 revolutions per second, yet scientists have found none that fast.
Courtesy: NASA
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| ITEM (5): Supernova Animation: Birth of a Pulsar - A supernova is associated with the death of a star about eighttimes as massive as the Sun or more. When such stars deplete their nuclear fuel, they no longer have the energy (in the form of radiation pressure outward) to support their mass. Their cores implode, forming either a neutron star (pulsar) or if there is enough mass, a black hole. The surface layers of the star blast outward, forming the colorful patterns typical of supernova remnants.
Courtesy: NASA
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