These Three Neutron Stars Shouldn't Be So Cold

Artist's impression of a neutron star, with white/blue filaments are streaming out from its polar regions, representing magnetic field lines. Credit: ESA

Neutron stars are among the densest objects in the Universe, second only to black holes. Like black holes, neutron stars are what remains after a star reaches the end of its life cycle and undergoes gravitational collapse. This produces a massive explosion (a supernova), in which a star sheds its outer layers and leaves behind a super-compressed stellar remnant. In fact, scientists speculate that matter at the center of the star is compressed to the point that even atoms collapse and electrons merge with protons to create neutrons.

Traditionally, scientists have relied on the “Equation of State” – a theoretical model that describes the state of matter under a given set of physical conditions – to understand what physical processes can occur inside a neutron star. But when a team led by scientists from the Spanish National Research Council (CSIC) examined three exceptionally young neutron stars, they noticed they were 10-100 times colder than other neutron stars of the same age. For this, the researchers concluded that these three stars are inconsistent with most of the proposed equations of state.

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The Most Massive Neutron Stars Probably Have Cores of Quark Matter

Illustration of a quark core in a neutron star. Credit: Jyrki Hokkanen, CSC - IT Center for Science

Atoms are made of three things: protons, neutrons, and electrons. Electrons are a type of fundamental particle, but protons and neutrons are composite particles made of up and down quarks. Protons have 2 ups and 1 down, while neutrons have 2 downs and 1 up. Because of the curious nature of the strong force, these quarks are always bound to each other, so they can never be truly free particles like electrons, at least in the vacuum of empty space. But a new study in Nature Communications finds that they can liberate themselves within the hearts of neutron stars.

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Can We Now Predict When A Neutron Star Will Give Birth To A Black Hole?

A black hole is the final form a massive star collapses to. The light (and spacetime itself) is warped around the black hole's event horizon due to extreme gravitational effects. This is as accurate as we can be to visualizing an actual black hole as it was generated with a code that implemented General Relativity accurately. Credit and Copyright: Paramount Pictures/Warner Bros. Mathematical Model used to create the image developed by Dr. Kip Thorne

A neutron star is perhaps one of the most awe-inspiring and mysterious things in the Universe. Composed almost entirely of neutrons with no net electrical charge, they are the final phase in the life-cycle of a giant star, born of the fiery explosions known as supernovae. They are also the densest known objects in the universe, a fact which often results in them becoming a black hole if they undergo a change in mass.

For some time, astronomers have been confounded by this process, never knowing where or when a neutron star might make this final transformation. But thanks to a recent study by a team of researchers from Goethe University in Frankfurt, Germany, it may now be possible to determine the absolute maximum mass that is required for a neutron star to collapse, giving birth to a new black hole.

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