(ORDO NEWS) — Neutron stars rise to the top of the list of the most interesting objects in the Universe. Now we have new evidence that the nuclei of the most massive neutron stars are made up of an exotic “soup” of subatomic particles called quarks.
Physicists made new calculations using data from gravitational waves first discovered as a result of a neutron star collision in August 2017, as well as observations of surprisingly massive neutron stars. Their conclusion hints at an exciting result – the nuclei of the most massive neutron stars are so dense that atomic nuclei cease to exist, condensing into quark matter.
According to the researchers, this is an important step in understanding the strange features of these extreme objects.
“Confirmation of the existence of quark cores inside the neutron star was one of the most important goals of the physics of neutron stars” – with Casal physicist Aleksi Vuorinen of the University of Helsinki and the Helsinki Institute of Physics.
Neutron stars are amazing objects. They are actually “dead” – the destroyed remains of massive stars, between 8 and 30 solar masses. When these stars become supernovae, most of their mass is thrown into space; the remaining core turns into an incredibly dense object.
The resulting neutron stars can range between 1.1 and 2.3 solar masses, packed in a dense small sphere with a diameter of only 10-20 kilometers.
When a supernova explosion occurs, the protons and electrons in the atoms that make up the object are compressed into neutrons and neutrinos. Neutrinos fly away, leaving neutrons under conditions of such high pressure that they fuse together, making the neutron star essentially one large core, whose density is 100 trillion times the density of water.
But it is expected that the density will increase as you go deeper, and it is here that the idea of nuclei from quark matter arises. Quarks are fundamental subatomic particles that combine to form compound particles such as protons and neutrons.
For several decades, astronomers have hypothesized that at a sufficiently high temperature and density, neutrons decay even further into their quarks, creating a kind of “quark soup”.
Although it’s really difficult to understand what is inside a neutron star. Thus, the collision in August 2017 – GW170817 – was very exciting for astronomers, since the way to change two stars when they became close enough to gravitationally deform each other could reveal information about their internal structure.
Vuorinen and his team used this gravitational wave signal along with new theoretical results and the results of particle physics to make calculations. They found that neutron stars in the direction of the upper mass limit of such objects – at least two solar masses – demonstrate characteristics that indicate the presence of a huge nucleus of quark matter, in more than half the diameter of a neutron star.
The discovery of quark matter inside neutron stars is not only surprising in itself – it can help us learn more about the earliest moments of our universe.
Cosmologists believe that for several microseconds immediately after the Big Bang, known as the era of quarks, the Universe was filled with hot “soup” from quark-gluon plasma, which quickly merged into hadrons.
Nowadays, we can only find quark matter in experiments with the collider for a very small period of time; but some massive neutron stars could also cover it. If we can characterize the conditions of a neutron star under which quark matter is formed, this could help us better understand the era of quarks.
Starting with GW170817, the LIGO-Virgo collaboration has discovered a second fusion of neutron stars, and it’s only a matter of time before new data begins to arrive. Analysis of new mergers can help the team confirm their calculations and smooth out uncertainties.
“There is reason to believe that the golden age of gravitational wave astrophysics is just beginning, and that soon we will witness many more such breakthroughs in our understanding of nature,” said Vuorinen.
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