Computer simulation of a merger between two dense neutron stars. After the merger, a phase transition from ordinary hadronic matter (red-yellow) to quark matter (green) takes place.
In the first fractions of a second of our universe's existence, the energy density was so incredibly high that there were no protons and neutrons, just a hot "quark soup" known as a quark-gluon plasma (QGP). Physicists have successfully recreated this unique state of matter in high-energy laboratories, but those conditions are exceedingly rare in the current cosmos. According to a new paper in the journal Physical Review Letters, German physicists have performed computer simulations indicating that a QGP could form in the immediate aftermath of a binary neutron star merger, and that it should produce a telltale, detectable signature in the gravitational waves emanating from that event.
"Compared to previous simulations, we have discovered a new signature in the gravitational waves that is significantly clearer to detect," said co-author Luciano Rezzolla of Goethe University in Frankfurt, Germany. "If this signature occurs in the gravitational waves that we will receive from future neutron-star mergers, we would have a clear evidence for the creation of quark-gluon plasma in the present universe."
A hot, dense soup
Quarks, the fundamental components of subatomic particles, are bound together by force-carrying gluons to form protons and neutrons. But under the extreme high-energy conditions of the early universe in its first microseconds of existence, that couldn't happen. Instead, quarks and gluons mingled freely in a dense soup, until things cooled down sufficiently for protons to condense out of the QGP. Before the first second was up, the Universe had gone through its entire inflationary period, sowing the seeds for the large-scale structures we see today.
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