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Astronomers have found the heaviest neutron star so far. This neutron star is called PSR J1614-2230. It is almost twice as heavy as our Sun. The team, including among others astronomer Jason Hessels from the University of Amsterdam (UvA), used the U.S. Green Bank Telescope in West Virginia for their observations

Astronomers have found the heaviest neutron star so far. This neutron star is called PSR J1614-2230. It is almost twice as heavy as our Sun. The team, including among others astronomer Jason Hessels from the University of Amsterdam (UvA), used the U.S. Green Bank Telescope in West Virginia for their observations. The result was published on 27 October 2010 in Nature.

A neutron star is the collapsed core of a massive star, which remains when the star explodes as a supernova at the end of its life cycle. The mass is compressed into a sphere with a diameter of only about 20 kilometres, as a result of which the protons and electrons are merged into neutrons. A neutron star can be even more compact than an atomic nucleus, and a teaspoon of neutron star material weighs more than 500 million tonnes. Due to the enormous density of the matter, neutron stars are natural laboratories in which the most extreme properties of matter can be studied.

Neutron Star PSR J1614-2230

In order to measure the mass of neutron star PSR J1614-2230 and its companion white dwarf, the astronomers used an effect that is explained by the General Theory of Relativity of Albert Einstein. This neutron star is actually a pulsar, which emits regular radio bursts, similar to the flashes of a rotating lighthouse. PSR J1614-2230 turns 317 times per second on its rotation axis, and orbits around its companion every nine days. This binary star system is about 3,000 light years away, with an orbital orientation that is very good for precisely measuring the mass of the two stars.

If the white dwarf is in front of the pulsar, the radio waves emitted from the pulsar have to pass close by that white dwarf. Because the white dwarf has a strong gravitational field, the pulses are delayed. This effect, called the Shapiro Delay, is used to determine the precise mass of the two stars.

‘We have been really lucky,' says Hesse. ‘The signal from the rapidly rotating pulsar could be measured almost perfectly. And because the white dwarf is quite heavy, we saw a very clear and easy to measure Shapiro Delay. We have also benefited from a new pulsar instrument at the Green Bank telescope.'

Previously, astronomers had estimated the mass of the pulsar at 1.4 solar masses. They were therefore surprised that it is actually almost twice as heavy as the Sun (1.97 solar masses). This much extra mass has a major impact on understanding the composition of such a star: some theoretical models predict exotic particles such as hyperons or kaons in a neutron star.