Gravitational waves created when two neutron stars collide may contain evidence of a previously unseen type of matter made of quarks.
Neutron stars form when massive stars run out of fuel and collapse. They are densely packed with neutrons, each of which contains three quarks held together by the strong nuclear force. When two neutron stars merge, their particles are so forcefully smashed that the quarks may be able to leave their neutron confinement and form a type of matter called quark matter. These mergers also result in space-time rippling with gravitational waves.
at the University of Notre Dame in Indiana and his colleagues have now used computer simulations to work out how gravitational waves could reveal the presence of quark matter in merging neutron stars.
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The researchers simulated two neutron stars colliding to see what frequency of gravitational waves would be produced in different situations, such as at different temperatures and densities. They found that when quark matter formed, the gravitational waves would have a set of frequencies peaking at about 3 kilohertz 鈥� a clear sign to look for.
Neutron star collisions are so extreme that they can鈥檛 be replicated in the lab, so it is challenging to study them, says at Kent State University in Ohio. 鈥淧eople have been speculating for a long time about the insides of neutron stars and what happens when they merge, but so much about the merger was hypothetical until 2017,鈥� she says.
In 2017, the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves emanating from a merger of two neutron stars. However, Mathews says that that measurement only captured waves with some frequencies, which was enough to determine that a merger happened but not enough to decisively pinpoint what happened inside the stars.
Some theories suggest that quark matter inside the neutron stars behaves similarly to perfect conductors of electricity while others posit that quark matter becomes an exotic fluid that then sloshes inside the stars with zero viscosity, says Mathews. His team鈥檚 simulations account for some of these scenarios, so they could be compared to upcoming measurements from LIGO and other detectors that will include more detailed gravitational wave frequencies to determine what actually happens.
鈥淭here are a lot of exciting things coming in the next two years, all the detectors have been upgraded, they will all measure more frequencies, and we will be able to learn more,鈥� says Dexheimer.
Mathews presented the at the in Hanoi, Vietnam, on 26 October.
