A planet made of diamondRead more.
Date posted: 26 Aug 2011
A planet made of diamond
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, reported today in Science, was made by an international research team led by Professor Matthew Bailes, Pro Vice-Chancellor (Research) at Swinburne University of Technology in Melbourne and the ‘Dynamic Universe’ theme leader in a new wide-field astronomy initiative, the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO).
The researchers, from Australia, Germany, Italy, the UK and the USA, first detected an unusual star called a pulsar using the CSIRO Parkes radio telescope 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 Centre 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.
The pulsar at the centre of the below image is orbited by an object that is about the mass of Jupiter and composed primarily of carbon; effectively a massive diamond. The orbit, represented by the dashed line, would easily fit inside our Sun, represented by the yellow surface. The blue lines represent the radio signal from the pulsar, which spins around 175 times every second.
Explanatory video from Professor Bailes
In the episode called Utopia from Doctor Who (2007), set 100 trillion years into the future before the universe is about to end, Martha Jones asked a child named Creet "What do you think it's going to be like in Utopia?" who replied "My Mum used to say the sky was made of diamonds."
Perhaps the diamond planet might be nicknamed Lucy.