'I Love Q' Equation Helps Understand The Universe

April Flowers for redOrbit.com – Your Universe Online

Without understanding the internal structure in detail, it is still possible for scientists to learn a tremendous amount about neutron stars and quark stars, according to a new study from researchers at Montana State University.

“The stars could be the softest or the hardest in their kind, and it wouldn’t matter,” said Nico Yunes, assistant professor in MSU’s Department of Physics. Yunes and his colleague, postdoctoral scholar Kent Yagi, discovered the reason for this: There are almost universal relations among three intrinsic properties of these highly compressed stars that will allow astrophysicists to discern the shape and degree of deformation in such stars without knowing the details of their internal structure. These relations, described in a recently published issue of Science, are realized among the moment of inertia (“I”), the “Love number” and the quadrupole moment (“Q”).

The first quantity, “ I,” describes how fast a star can rotate, with larger numbers denoting slower spin rates.

“Think of twirling ice skaters,” Yagi said. “If they bring their arms close to their bodies, the skaters’ moment of inertia decreases, and so they spin faster.”

The deformability of a star when squished is represented by the Love number – named after its discoverer Augustus Edward Hough Love. The more deformed a star is, the larger the Love number. “Q,” the third quantity, refers to the changing shape of a star.

According to the new study, the measurement of any one of these three quantities would allow scientists to infer the other two with amazing precision, without actually having to measure them directly.

“It doesn’t matter if the star is made of different proportions of neutrons, quarks and other particles. In the end, how much the star can be squeezed will be a direct function of its moment of inertia,” Yagi said.

The researchers employed mathematical equations and computer models to discover that I, Love and Q satisfy these universal relations.

Neutron and quark stars are extremely compact, containing an enormous amount of mass in a tiny radius. This combination means that the stars are so dense that they exert an immensely strong gravitational pull.

“Just imagine a ball the size of the sun being squeezed until it’s the size of Bozeman,” he said. “All the gravity of the sun, but amplified by factors of thousands.”

As the stars spiral into each other and collide, astrophysicists believe they produce waves that vibrate through the universe. They predict being able to detect these “gravitational” waves within the next ten years, which could open up a whole new avenue for understanding the universe.

“To make a simple analogy, these waves are like the soundtrack to the universe, and their detection will be like transitioning from mute pictures to modern cinema,” Yunes said.

The I-Love-Q relations will also aid in the gravitational wave effort, Yunes and Yagi suggest.

“For instance, this universal relation could be used to test Einstein’s Theory of General Relativity without contamination due to our ignorance of their internal structure,” Yunes said. “You could also use these relations to tell whether what you have observed is a neutron star or a strange quark star.”

“Not understanding the internal structure of neutron stars has presented a major challenge to certain astrophysical studies, but the “I Love Q relations show that you can proceed without that knowledge,” Yunes said.

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