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Nuclear cooling in neutron stars deepens mystery of hot surface

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supernovax250Research by a team of scientists led by a Michigan State Univ. (MSU) physicist has shed new light on the properties of neutron stars, super dense stars that form when a large star explodes and collapses into itself.

Writing in Nature, Hendrik Schatz and colleagues describe a newly discovered process that happens within the star’s crust, located just below the surface. Until now, scientists thought that nuclear reactions within the crust contributed to the heating of the star’s surface.

“We previously thought that these reactions were strong enough to heat up the crust,” said Schatz, an MSU prof. of physics and astronomy. “But that’s not the case.”

What the team of scientists found is that in the star’s crust near the surface there is a layer where nuclear reactions cause rapid neutrino cooling. Neutrinos are very elementary particles that are created through radioactive decay and pass very quickly through matter.

“These cooling layers are pretty shallow beneath the surface,” Schatz said. “If heat from deeper within the star comes up, it hits one of these layers and never makes it to the surface.”

Schatz said this discovery produces more questions than answers.

“This completely changes the way we think about the question of the hot surface,” he said. “It’s a big puzzle now.”

On the sub-atomic level, the team found that the process is greatly affected by the shape of the reacting nuclei. “Many nuclei are round and that suppresses the neutrino cooling. In this case, the nuclei are predicted by theorists to be “deformed,” more football-shaped”, said Sanjib Gupta, a former JINA and LANL (Los Alamos National Laboratory) postdoctoral researcher, now a faculty member at IIT Ropar in India.

This is also significant as MSU seeks to build the Facility for Rare Isotope Beams. FRIB will be a new U.S. Dept. of Energy Office of Science national user facility. It is exactly these types of nuclei that researchers could examine in the facility.

This work was enabled by the Joint Institute for Nuclear Astrophysics, or JINA, project that brings together astrophysicists and nuclear physicists to collaborate. JINA is a National Science Foundation Physics Frontiers Center on Nuclear Astrophysics. MSU is one of the core institutions of JINA, which was founded in 2003.

Study Abstract

http://www.rdmag.com/news/2013/12/nuclear-cooling-neutron-stars-deepens-mystery-hot-surface

Written by physicsgg

December 2, 2013 at 9:28 pm

Posted in ASTRONOMY, ASTROPHYSICS

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Neutron star blows away models for thermonuclear explosions

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Amsterdam astronomers have discovered a neutron star that confounds existing models for thermonuclear explosions in such extreme objects. In the case of the accreting pulsar IGR J17480-2446, it seems to be a strong magnetic field that causes some parts of the star to burn more brightly than the rest. The results of the study, by Yuri Cavecchi et al. (2011), are to be published in the journal Astrophysical Journal Letters.
The neutron star concerned is part of the X-ray binary IGR J17480-2446 (hereafter J17480). X-ray binaries consist of a neutron star and a companion star in orbit around each other. Neutron stars, which are about 1.5 times as massive as the Sun, with a diameter of about 25 km, have a strong gravitational field that can pull gas from the companion star. This gas can build up on the neutron star surface and explode in a fast, high-energy thermonuclear reaction. Normally, the entire surface of the star explodes uniformly. However, in about 10 percent of cases, some parts of the star become much brighter than the rest. Why this occurs is not understood……. Read the rest of this entry »

Written by physicsgg

September 18, 2011 at 4:16 pm

Posted in ASTRONOMY, ASTROPHYSICS

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