Merging neutron stars to reveal secrets about the structure of matter | Science & Tech News


Measuring the grativational waves produced by the merging of two neutron stars will reveal secrets about the fundamental structure of matter in the universe, according to scientists.

Neutron stars are the among the most dense objects in the universe, composed of the core of a collapsed star that did not form a black hole.

Scientists believe that when they crash into each other they may prompt a phase transition in which neutrons dissolve into the sub-atomic particles of quarks and gluons.

New research published in Physical Review Letters has reported the calculations of two international groups of scientists of what such a phase transition would look like in a gravitational wave.

Quarks are the smallest particles which form matter. They never appear alone and are bound inside larger particles such as protons and neutrons.

In the core of neutron stars, which could weigh as much as the sun but measure the size of a city, matter can be packed so densely that neutrons could dissolve into quarks.

This kind of transition is known as a phase transition to physicists and is similar to the phase transition when water boils and becomes steam or vapour.

Essentially, such a transition is theoretically possible when neutron stars merge to form a density so high that atoms themselves are crushed at temperatures 10,000 times higher than in the core of the sun.

Measuring gravitational waves emitted from merging neutron stars would be a great way to detect such a phase transition, according to the scientists.

They believe it would leave a special signature in the wave signal, and have used supercomputers to figure out what this signature could look like.

“With aid of the Einstein equations, we were able to show for the first time that this subtle change in the structure will produce a deviation in the gravitational wave signal until the newly formed massive neutron star collapses under its own weight to form a black hole,” explained Professor Luciano Rezzolla, who is a professor for theoretical astrophysics at Goethe University.

The computer models of Dr Andreas Bauswein differ slightly, but also show a specific signature in the gravitational wave signal.

“We succeeded to show that in this case there will be a distinct shift in the frequency of the gravitational wave signal,” said Dr Bauswein.

“Thus, we identified a measurable criterion for a phase transition in gravitational waves of neutron star mergers in the future.”

The difference is about when the quarks appear, whether small amounts gradually develop throughout the merged object or if a core of quark matter begins to form at the object’s interior.

Unfortunately, some of the qualities of the gravitational wave signal which could identify which phase transition takes place would be unmeasurable with current detectors.

But a new generation of technology and a merger event relatively close to the Earth could allow this special signature to be identified.

By detecting which of the gravitational wave signatures the scientific groups have proposed is actually emitted by the merger event, scientists could gain crucial new insights into phase transitions in nuclear matter, and thus into how that matter is structured.

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