“Unveiling the Cosmos: LIGO’s Quest for Neutron-Star Mountain Gravitational Waves”

Moons in the Solar System, like Europa and Enceladus, possess thin crusts above extensive oceans, while the planet Mercury features a slender crust over a substantial metallic core. These thin layers might exhibit wrinkling in universal patterns. Europa displays linear characteristics, Enceladus features ‘tiger stripes,’ and Mercury is noted for its lobate scarps. Neutron stars might present similar traits. Recent studies indicate that these mountains on neutron stars could generate noticeable oscillations of space-time, referred to as gravitational waves.

An artist’s impression of a neutron star. Image credit: Sci.News.

Neutron stars possess a density a trillion times greater than that of lead, and their surface characteristics remain mostly unexplored.

Nuclear theorists investigated the mechanisms of mountain formation occurring on the moons and planets within our Solar System.

Several of these processes propose that neutron stars are probably adorned with mountains.

The mountains on neutron stars would greatly exceed any found on Earth—so massive that the gravitational influence from these elevations could lead to the creation of gravitational waves.

The Laser Interferometer Gravitational Wave Observatory (LIGO) is currently on the lookout for these signals.

“These waves are extremely faint, detectable only through highly detailed and sensitive searches that are precisely adjusted to expected frequencies and other signal characteristics,” remarked Jorge Morales and Professor Charles Horowitz, nuclear astrophysicists from Indiana University.

“The initial observations of continuous gravitational waves will unveil a new perspective on the Universe and yield exclusive insights into neutron stars, the densest entities outside of black holes.”

“These signals may also facilitate sensitive evaluations of fundamental principles of nature.”

The researchers drew parallels between the mountains of neutron stars and the surface features of bodies within the solar system.

“Both neutron stars and specific moons, like Europa of Jupiter or Enceladus of Saturn, exhibit thin crusts over vast oceans, while Mercury features a thin crust sitting above a large metallic core. These slender layers may wrinkle in universal patterns,” they explained.

“Europa has linear traits, Enceladus has stripes reminiscent of tigers, and Mercury showcases curved, step-like formations.”

“Neutron stars with mountainous structures may display similar surface characteristics, which could be uncovered through the observation of continuous gravitational wave signals.”

“The innermost interior core of the Earth exhibits anisotropic qualities with a shear modulus that varies with direction.”

“Should the crust material of neutron stars also be anisotropic, a formation resembling a mountain will emerge, and its elevation will increase as the star spins more rapidly.”

“Such a surface characteristic could account for the maximum spin rate observed in neutron stars and the potential minimum deformation seen in radio-emitting neutron stars known as millisecond pulsars.”

The team’s publication was released in the journal Physical Review D.

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J.A. Morales & C.J. Horowitz. 2024. Anisotropic neutron star crust, solar system mountains, and gravitational waves. Phys. Rev. D 110, 044016; doi: 10.1103/PhysRevD.110.044016