Tuesday, March 25, 2014

SISSA: Simple, like a neutron star

For astrophysicists neutron stars are extremely complex astronomical objects.

Research conducted with the collaboration of SISSA and published in the journal Physical Review Letters demonstrates that in certain respects these stars can instead be described very simply and that they show similarities with black holes.

In how many ways can one describe an object?

Take an apple: by just looking at it we can easily estimate its weight, shape and colour but we are unable to describe it at any other level, for example, to evaluate the chemical composition of its flesh.

Something similar also applies to astronomical objects: until today one of the challenges facing scientists was to describe neutron stars at the nuclear physics level.

The matter these stars are made up of is in fact extremely complex, and several complicated equations of state have been proposed.

However, to date there is no agreement as to which is the correct (or the best) one.

A theoretical study conducted by SISSA (the International School for Advanced Studies of Trieste), in collaboration with Athens University, has demonstrated that neutron stars can also be described in relatively simple terms, by observing the structure of the space-time surrounding them.

"Neutron stars are complex objects owing to the matter that composes them. We can picture them as enormous atomic nuclei with a radius of about ten kilometres", explains Georgios Pappas, first author of the study carried out at SISSA.

"A neutron star is what remains of the collapse of a massive star: the matter inside it is extremely dense and mostly consisting of neutrons".

"The nuclear physics required to understand the nature of the matter contained in these astronomical objects generally makes their description very complicated and difficult to formulate," continues Pappas.

"What we have demonstrated, by using numerical methods, is that there are properties that can provide a description of some aspects of neutron stars and the surrounding space-time in a simple manner, similar to the description used for black holes".

Black holes are truly unique objects: they have lost all matter and are only made up of space and time. Just like neutron stars they are the result of the collapse of a bigger star (in this case much bigger than the stars giving rise to neutron stars) and in the implosion all the matter has been swept away.

"They are considered to be the most perfect objects in the Universe and the expression 'hairless' that was coined by John Archibald Wheeler to indicate their simplicity has become famous. According to our calculations even neutron stars can be depicted in a very similar manner".

More Information: 'Effectively universal behaviour of rotating neutron stars in general relativity makes them even simpler than their Newtonian counterparts' Authors: George Pappas and Theocharis A. Apostolatos - Phys. Rev. Lett.

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