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Neutron star mountains much higher than expected
Published: 15 April, 2009, 13:36
Simulations have shown that a superdense neutron star crust is much harder than expected and can support big ‘mountains’. This raises hope for registering gravitational waves soon.
Computer modeling at the Los Alamos National Laboratory in the US has shown that a neutron star crust can withstand about ten billion times more pressure than earthly stainless steel before breaking. The number is 10 times higher than was previously estimated, and suggests a neutron star can have irregularities on its surface big enough to generate powerful gravitational waves, reports New Scientist magazine.
Neutron stars are the remnants of big stars that explode in supernovae. Their matter is densely compressed by gravity so that a star with a mass about double that of the Sun has a diameter of just a dozen kilometres.
They also rotate at high speed due to the conservation of angular momentum. When the progenitor star explodes, the rotation of its core greatly increases similar to what happens when figure skaters pull their arms closer to their body to increase spin. A newborn neutron star may make a hundred turns in a second.
Thanks to these properties neutron stars can potentially generate gravitational waves, which are ripples in the fabric of time-space caused by the regular movement of massive objects. The waves have been predicted and there is indirect evidence of their existence, but so far astronomers have failed to observe them directly due to their very low strength.
To generate the waves, neutron stars need to have an irregular surface. Stable bumps on the star’s crust may result from matter pulled by a neutron star from an accompanying star in a binary system.
“All else being equal, the maximum height of a 'mountain' on a neutron star is now ten times what we thought,” Benjamin Owen of Pennsylvania State University told the journal.
Bigger bumps means the gravitational waves they generate are much stronger than the scientists expected, and potentially they can be detected directly by ground-based experiments, like the US Laser Interferometer Gravitational-Wave Observatory.
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