Space Travel
12, Feb, 2012

Astronomers Measure Neutrons Stars Crust
Written by spacetravel.org   
Monday, 01 May 2006 12:00
Astronomers have measured the thickness of the crust of a neutron star for the first time. The technique, which involves studying how the dense stellar corpse reverberates during a "starquake", may one day reveal the nature of the exotic matter thought to lie at the star's core. Neutron stars form when stars up to 40 times the mass of the Sun explode at the end of their lives and leave behind super-dense, spinning corpses. The corpses are thought to be made of neutrons, although their incredible densities have led some researchers to propose their centres contain a state of matter found nowhere else in the universe.

Now, a team led by Tod Strohmayer of NASA's Goddard Space Flight Center in Greenbelt, Maryland, US, has begun to probe the actual structure of the stars. Using data from NASA's Rossi X-ray Timing Explorer, the researchers measured the frequencies of vibrations on a star called SGR 1806-20 during a starquake in December 2004.

"We think this explosion, the biggest of its kind ever observed, really jolted the star and literally started it ringing like a bell," says Strohmayer. "The vibrations created in the explosion, although faint, provide very specific clues about what makes up these bizarre objects."

The team found a high-frequency oscillation of 625 Hz, which suggested the waves were ringing through the crust vertically. This, along with the other frequencies measured, led the researchers to estimate the crust's thickness at about 1.5 kilometres. The entire neutron star is only thought to span about 20 kilometres across.

"That's pretty thick, but not ridiculous," says Stephen Eikenberry, an astrophysicist at the University of Florida in Gainesville, US. "So far, all we had for understanding the structure of neutron stars is really just theoretical models. So having the measurement is very exciting."

The team says it could probe even deeper into the structure of neutron stars if it could analyse the vibrations from an even more powerful starquake. Eikenberry says such a mighty explosion may indeed be possible, and agrees that it could reveal the nature of the stars. "A bigger event might let us peer all the way to the centre of the neutron star and see what it's made of."

Such an event could reveal whether the stars are composed simply of neutrons or whether they contain free-roaming quarks or other exotic particles. Quarks are subatomic particles that make up protons and neutrons and have so far only been observed bound together in groups. But some theorists think that the incredible densities inside neutron stars may allow the quarks to break free of each other.

Source: New Scientist
< Prev   Next >