Rotation of Neutron Star Influences Rate of Thermonuclear Explosions at Surface

cluster image

(Best Syndication News) Scientists have been studying neutron stars for decades and believe they have discovered one that could change the way they view their behavior.

Neutron stars are typically small, perhaps just 10 miles in width, but contain up to two solar masses. They are created when a massive star collapses after a supernova event. Several years ago scientists spotted eruptions on IGR J17480–2446, a neutron star near our galaxy’s center. They dubbed the neutron star, which is orbiting a star about the size of our sun, T5X2.

In 2010 astronomers noticed hundreds of X-ray bursts that were powered by a barrage of thermonuclear explosions on the neutron star's surface. T5X2, which lies about 25,000 light years from earth, began to emit regular pulses like a pulsar.

Through accretion, matter is being transferred from the star to the neutron star. Explosions occur as the matter makes contact with the neutron star.

Most of the gas is being pulled to the magnetic poles producing hot spots that rotate with the neutron star giving off X-ray pulses. The neutron star has been rotating at 11 times per second, which is considered slow for neutron stars, and makes a complete orbit around the star once every 21 hours.

The behavior of the neutron bursts have been unusual, according to Manuel Linares, a postdoctoral researcher at the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology in Cambridge.

“In a single month from this unique system, we have identified behavior not seen in observations of nearly 100 bursting neutron stars during the past 30 years," Linares said.

The accretion rate of 5X2 is slow, according to Linares. There have been long “lulls” between the pulses, as the matter builds up before the nuclear explosions. But in higher rates of accretion the flow of fuel onto the neutron star can support continuous and stable thermonuclear reactions without building up and triggering episodic explosions.

The observation is in line with their expectations. "We see T5X2 as a 'model burster,' the one that's doing everything expected of it," said Diego Altamirano, an astrophysicist at the University of Amsterdam in The Netherlands and a co-author on the paper describing the findings.

They believe T5X2 is different from other observed neutron stars because of the slow rotation. Neutron stars with a faster rotation create more friction between the surface and the accretion gasses. The extra heat from the friction alters the nuclear burn rate.

The research will be published in the March 20 issue of The Astrophysical Journal.

By: Julie Marcus
Science Reporter

Image: Terzan 5 cluster containing T5X2



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