Neutron stars, the smallest and most dense stars in the universe emerging from a supernova explosion, have been found to hide truly exotic structures - quark matter, a phenomenal result of nuclear matter collapsing in the star's core, a study published by Finnish scientists in the journal Nature Physics suggests.
"Confirming the existence of quark cores inside neutron stars has been one of the most important goals of neutron star physics ever since this possibility was first entertained roughly 40 years ago", said theoretical physicist Aleksi Vuorinen of the University of Helsinki and the Helsinki Institute of Physics.
Packed into a dense, small sphere only 10 to 20 kilometres (6.2 to 12.4 miles) across, neutron stars are incredibly heavy, averaging about 1.1 and 2.3 solar masses, and it has been extremely difficult to find out what’s hidden inside.
However, the scientists managed to produce calculations based on an unparalleled event from 2017 - the collision codenamed GW170817, in which two stars changed as they approached each other close enough to gravitationally deform each other.
Having used that gravitational wave signal along with new theoretical and particle physics results, Vuorinen and his team came to believe that neutron stars towards the upper mass limit of such objects - at least 2 solar masses - show characteristics that indicate the presence of a huge quark matter core, more than half the neutron star's entire diameter.
The researchers’ simulations indicate that something really peculiar would have to be going on, if the cores of these stars are not composed of quark matter: they have hitherto been considered to look like some “nuclear pasta” - a result of the protons and electrons in the atoms being compressed into neutrons and neutrinos.
“There is still a small but nonzero chance that all neutron stars are composed of nuclear matter alone", Dr Vuorinen acknowledged, saying they have been able to “quantify that the scenario would require".
“In short, the behaviour of dense nuclear matter would then need to be truly peculiar. For instance, the speed of sound would need to reach almost that of light", Vuorinen exemplified.
Along with being stunning just as such, the discovery of quark matter hidden in the very core of neutron stars promises to help astrophysicists to learn more about the dawn of our universe.
Cosmologists believe that, for a few brief moments just after the Big Bang known as "the quark epoch", the universe was filled with a hot soup of quark-gluon plasma that rapidly coalesced into hadrons, another type of elementary particles.
