Neutron stars and black holes

When massive stars reach the end of their lives nuclear burning can no longer support them against gravity. The resulting collapse triggers a violent supernova explosion. The core of the parent star collapses down to a compact remnant: a neutron star or a black hole, and the outermost layers are blown away.

Neutron stars

Neutron stars contain up to twice the mass of our Sun in a sphere the size of Amsterdam (the Sun, by contrast, is 1.4 million kilometers across). This makes them excellent laboratories for extreme physics. Neutron stars are so dense that atomic nuclei dissolve into their constituent protons and neutrons. The nature of matter under these conditions is very poorly understood, and exotic nuclear physics states such as superconducting quarks, or a quark-gluon plasma, may form in neutron star cores. Neutron stars have the strongest magnetic fields in the Universe, a staggering 10 orders of magnitude larger than the strongest fields we can create, for fractions of a second, in laboratories on Earth. The gravitational field of a neutron star is also a hundred billion times that of the Earth, strong enough we can use them to test key aspects of the Theory of General Relativity.

Researchers at API study many different aspects of neutron stars, using a mix of observations and theoretical calculations. API astronomers observe neutron stars across the electromagnetic spectrum, from low frequency radio waves all the way up to the highest energy gamma-rays. We even study them using gravitational waves, a completely new field of astronomy.

Black holes

Black holes are one of the most extreme predictions of Einsteins General Theory of Relativity. When a collapsing star core is more massive than the maximum mass a neutron star can sustain, total gravitational collapse occurs. All matter is destroyed and its mass is concentrated in a pointlike object called the singularity that contains all the mass of the collapsing core. No physical theory in existence can precisely describe the nature of this singularity, but Einsteins theory allows a accurate description of its effect on the surroundings. The extreme gravity associated with the collapsed core warps spacetime in such a way that a black spherical surface forms called the 'event horizon'. This horizon has the property that physical objects and radiation can go in, but can never escape. The singularity is therefore hiden behid it. The horizon has many other curious properties, such as the fact that, as seen from far away, on the horizon time stands still, but when one approaches it this is not the case. Anything that falls through the horizon into the black hole ends up in the singularity and is crushed.

Extreme though these predicitions may be, black holes do appear to occur in Nature, not only in the form of collapsed star cores just like neutron stars, but also as supermassive black holes at the centers of most galaxies (including a 4 million Solar mass black hole right in the heart of our own Milke Way galaxy). API astronomers observe black holes in all the same ways as neutron stars: although the holes themselves are black and therefore emit no radiation, matter that orbits near to them can get very hot and produce all kinds of radiation.

People at The Institute are working on the following topics:

Accreting X-ray binaries

Accretion and jet formation

Neutron star crust cooling

Neutron starquakes

Radio pulsars