|
|
|
|
|
Hidden structure of neutron star seen in starquake NASA-GSFC NEWS RELEASE Posted: April 24, 2006 Scientists using NASA's Rossi X-ray Timing Explorer have estimated the depth of the crust on a neutron star, the densest object known in the universe. The crust, they say, is close to a mile deep and so tightly packed that a teaspoon of this material would weigh about 10 million tons on Earth. The measurement, the first of its kind, came courtesy of a massive explosion on a neutron star in December 2004. Vibrations from the explosion revealed details about the star's composition. The technique is analogous to seismology, the study of seismic waves from earthquakes and explosions that reveal the structure of the Earth's crust and interior. This new seismology technique provides a way to probe a neutron star's interior, a place of great mystery and speculation. Pressure and density are so intense here that the core might harbor exotic particles thought to have existed only at the moment of the Big Bang. Tod Strohmayer of NASA Goddard Space Flight Center in Greenbelt, Md., presents this result in a press conference today at the April meeting of the American Physical Society in Dallas. His colleague, Anna Watts, formerly at Goddard, is now at the Max Planck Institute for Astrophysics in Germany. "We think this explosion, the biggest of its kind ever observed, really jolted the star and literally started it ringing like a bell," said Strohmayer. "The vibrations created in the explosion, although faint, provide very specific clues about what makes up these bizarre objects. A neutron star's ring depends on how waves pass through layers of differing density, either slushy or solid." A neutron star is the core remnant of a star once several times more massive than the sun. A neutron star contains about 1.4 solar masses of material crammed into a sphere only about 12 miles across. Strohmayer and Watts examined a neutron star named SGR 1806-20, about 40,000 light years from Earth in the constellation Sagittarius. The object is in a subclass of highly magnetic neutron stars called magnetars. On December 27, 2004, the surface of SGR 1806-20 experienced an unprecedented explosion. As reported by NASA and the National Science Foundation in early 2005, this was the brightest X-ray flash ever seen from beyond our solar system. The explosion, called a hyperflare, was caused by a sudden change in the star's powerful magnetic field that cracked the crust, likely producing a massive starquake. The event was detected by several space observatories, including the Rossi Explorer, which observed the X-ray light emitted. Strohmayer and Watts think that the oscillations are evidence of global torsional vibrations within the star's crust. These vibrations, like waves moving through a rope, are analogous to the S-waves observed during terrestrial earthquakes. Their study, building on observations of vibrations from this source by GianLuca Israel of Italy's National Institute of Astrophysics, found several new frequencies during the hyperflare. Watts and Strohmayer subsequently confirmed their measurements using NASA's Ramaty High Energy Spectroscopic Solar Imager, a solar observatory that also recorded the hyperflare. And they found the evidence for a high-frequency oscillation at 625 Hz, indicative of waves traversing the crust vertically. The abundance of frequencies---similar to a chord, as opposed to a single note---enabled the scientists to estimate the depth of the neutron star crust. This is based on a comparison of frequencies from waves traveling around the star's crust and from those traveling radially through it. The diameter of a neutron star is uncertain, but based on the estimate of about 12 miles across, the crust would be about 1 mile deep. This figure, based on the observed frequencies, is in line with theoretical estimates. Starquake seismology holds great promise for determining many neutron star properties. Strohmayer and Watts have analyzed archived Rossi data from a dimmer 1998 magnetar hyperflare (from SGR 1900+14) and found telltale oscillations here, too, although not strong enough to determine the crust thickness. A larger neutron star explosion detected in X-rays might reveal deeper secrets, such as the nature of matter at the star's core. One exciting possibility is that the core might contain free quarks. Quarks are the building blocks of protons and neutrons, and under normal conditions are always tightly bound together. Finding evidence for free quarks would aid in understanding the true nature of matter and energy. Laboratories on Earth, including massive particle accelerators, cannot generate the energies needed to reveal free quarks. "Neutron stars are great laboratories for the study of extreme physics," said Watts. "We'd love to be able to crack one open, but since that's probably not going to happen, observing the effects of a magnetar hyperflare on a neutron star is perhaps the next best thing." |
|
|
|
 |
||||||||||||||||||||
The Lockheed Martin Atlas 5 rocket blasts off with the European ASTRA 1KR television broadcast satellite right on time April 20 from Complex 41 at Cape Canaveral Air Force Station.
Soon after the Palapa and Westar communications satellites got stranded in worthless orbits following their deployment from shuttle Challenger in February 1984, planners began devising a rescue mission to launch that November. The STS-51A flight of shuttle Discovery is arguably one of the most daring and complex space missions ever attempted. The crew successfully launched two communications satellites and then retrieved Palapa and Westar during extraordinary spacewalks using jet-propelled backpacks and hands-on muscle power. Watch the amazing flight unfold with narration by the crew in this post-flight film.
In the continuing 25th anniversary celebration of STS-1, this program looks at the engineering challenges behind development of the space shuttle and performing the first flight from Mission Control. This panel includes Milt Heflin, the STS-1 ascent/entry electrical power system flight controller, former space shuttle program manager Bob Thompson, former orbiter project manager Aaron Cohen, Neil Hutchinson, the STS-1 ascent flight director, and astronauts John Young and Bob Crippen.
This 25th anniversary celebration of the first space shuttle launch took place April 12 at Space Center Houston. Speakers included Johnson Space Center Director Mike Coats, NASA Administrator Mike Griffin, Congressman Tom DeLay, Senator Kay Bailey Hutchison, STS-1 commander John Young and pilot Bob Crippen. 
During this NASA news conference on April 10, agency officials unveil the Lunar Crater Observation and Sensing Satellite, or LCROSS, that will launch piggyback with the Lunar Reconnaissance Orbiter spacecraft in October 2008. LCROSS will use the launch vehicle's spent upper stage to crash into the moon's south pole in an explosive search for water.
Daniel Andrews, the LCROSS project manager from NASA's Ames Research Center, narrates this animation depicting the mission from launch through impact on the lunar surface.
In this highly entertaining program, commander John Young and pilot Bob Crippen of the first space shuttle crew tell stories and memories from STS-1. The two respected astronauts visited Kennedy Space Center on April 6 to mark the upcoming 25th anniversary of Columbia's maiden voyage.