Monday, January 9, 2012

The Right Pitch to Shatter a Neutron Star

Our paper on crust shattering of neutron stars was spotlighted by PRL and given a synopsis by a science writer! It was later picked up in the news! This is the New Scientist article. Another article about it is in ArsTechnica and the paper is even referred to on wikipedia when precursors to short Gamma Ray Bursts (sGRBs) are mentioned. This work resulted from a collaboration with David Tsang (Caltech), Jocelyn Read (University of Mississippi), Tanja Hinderer (Caltech), and Tony Piro (Caltech), which was lead by Dave and Jocelyn.

The paper is about a potential explanation for precursors of short Gamma Ray Bursts (sGRBs). GRBs are some of the most luminous events in the universe outshining any other gamma ray source in the sky*. Their high luminosity coupled with their short emission timescales implies an enormous amount of energy must released from a small volume of space ( 100km). They typically have isotropic equivalent luminosities of 1017 x the luminosity of the sun over a duration of less than 2 seconds. These highly luminous bursts are seen by the NASA's Swift and Fermi telescopes.

A leading model for sGRBs is the neutron star- neutron star merger. As the two neutron stars in the binary get closer together, the tidal frequency increases. The neutron star crust is believed to be very stiff and can have a resonant frequency just like glass.  When the tidal frequency matches the resonant frequency of the crust, the crust shatters just like a wine glass shatters when an opera singer hits the right note and excites high energy emission, which can explain the flares seen just prior to sGRBs.

From David Tsang, Caltech
Here is Dave's fancier summary: "Can neutron stars, dead stars composed of exotic material trillions of times more dense than a normal star, shatter like an ordinary wine glass? Our new research shows that indeed they can. As a neutron star spirals in towards another neutron star or black hole due to emission of gravitational waves, tidal forces act on the star with increasing frequency. When this frequency matches the resonance frequency of the neutron star crust -- just like an opera singer hitting the right note for a wine glass -- the crust shatters. The shattering crust may excite high-energy emission, explaining gamma-ray flares seen just prior to short gamma-ray bursts. Just as the note at which a wineglass shatters tells you about the composition and shape of that wineglass, studying the timing of these flares could allow physicists to learn about the properties of dense matter in neutron star crusts, material that cannot be probed by ordinary terrestrial experiments."

An opera singer and a broken glass can be seen below:

Disclaimer: Unfortunately, I do not know who are the authors of either the opera singer or the broken glass photo.

*Gamma rays are light of very high frequency of over 1019 Hz (more than 1 000 000 times the frequency of visible light) and wavelengths of less than 10 pm (a tenth of the diameter of an atom). Light of very high frequency also has very high energy.

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