A Planet Made of Diamond

An artist's visualisation of the pulsar and its orbiting planet. Image credit - Swinburne Astronomy Productions



by Staff Writers
Canberra, Australia (SPX) Aug 26, 2011



A once-massive star that's been transformed into a small planet made of diamond: that's what astronomers think they've found in our Milky Way.

The discovery has been made by an international research team, led by Professor Matthew Bailes of Swinburne University of Technology in Melbourne, Australia, and is reported in the latest issue of the journal Science.

Although bizarre, the "diamond planet" is in accord with our current picture of how certain binary star systems form.

The researchers, from Australia, Germany, Italy, the UK and the USA first detected an unusual star called a pulsar using the 64-m Parkes radio telescope of the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) and followed up their discovery with the Lovell radio telescope in the UK and one of the Keck telescopes in Hawaii.

Pulsars are small spinning stars about 20 km in diameter - the size of a small city - that emit a beam of radio waves. As the star spins and the radio beam sweeps repeatedly over Earth, radio telescopes detect a regular pattern of radio pulses.

For the newly discovered pulsar, known as PSR J1719-1438, the astronomers noticed that the arrival times of the pulses were systematically modulated. They concluded that this was due to the gravitational pull of a small companion planet, orbiting the pulsar in a binary system.

The pulsar and its planet are part of the Milky Way's plane of stars and lie 4,000 light-years away in the constellation of Serpens (the Snake). The system is about an eighth of the way towards the galactic center from the Earth.

The modulations in the radio pulses tell astronomers several things about the planet.

First, it orbits the pulsar in just two hours and ten minutes, and the distance between the two objects is 600,000 km - a little less than the radius of our Sun.

Second, the companion must be small, less than 60,000 km (that's about five times the Earth's diameter). The planet is so close to the pulsar that, if it were any bigger, it would be ripped apart by the pulsar's gravity.

But despite its small size, the planet has slightly more mass than Jupiter.

"This high density of the planet provides a clue to its origin", said Professor Bailes.
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