August 26, 2011

Scientists Discover ‘Diamond Planet’


An international team of astronomers has discovered an exotic planet that appears to be made of diamond orbiting a tiny star in our galaxy.

The new planet, which is far denser than any other previously known, consists primarily of carbon.  However, its high density has led scientists to calculate the carbon must be crystalline, meaning a large part of the planet would effectively be diamond.

"The evolutionary history and amazing density of the planet all suggest it is comprised of carbon -- i.e. a massive diamond orbiting a neutron star every two hours in an orbit so tight it would fit inside our own Sun," said Matthew Bailes of Swinburne University of Technology in Melbourne, Australia.

The astronomers first detected an unusual star known as a pulsar -- a small spinning star about 12 miles in diameter that emits a beam of radio waves — using the Parkes radio telescope of the Australian Commonwealth Scientific and Industrial Research Organization (CSIRO).  

As pulsars spin, their radio beam sweeps repeatedly over Earth, allowing radio telescopes to detect a regular pattern of radio pulses.

The researchers then followed up on their discovery using the Lovell radio telescope based at Jodrell Bank Observatory in Cheshire, and one of the Keck telescopes in Hawaii.

For the newly discovered pulsar, known as PSR J1719-1438, the astronomers noticed that the arrival times of the pulses were systematically modulated, something they attributed 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 system is about an eighth of the way towards the Galactic Center from the Earth.

The modulations in the radio pulses tell astronomers a number of things about the planet.  First, it orbits the pulsar in just two hours and ten minutes, and the distance between the two objects is 375,000 miles–slightly less than the radius of the Sun.  Second, the companion must be small, less than 38,000 miles in diameter, or about five times the size of the Earth.  The planet is so close to the pulsar that, if it were any bigger, it would be ripped apart by the pulsar's gravity, the astronomers said.

However, 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 team thinks that the 'diamond planet' is all that remains of a once-massive star, most of whose matter was siphoned off towards the pulsar.

Pulsar J1719-1438 is a very fast-spinning pulsar, something known as a millisecond pulsar.   Indeed, it rotates more than 10,000 times per minute, has a mass of about 1.4 times that of our Sun but is only 12 miles in diameter.  

Roughly 70 percent of millisecond pulsars have companions of some kind.

Astronomers believe it is the companion that, in its star form, transforms an old, dead pulsar into a millisecond pulsar by transferring matter and spinning it up to a very high speed.  The result is a fast-spinning millisecond pulsar with a shrunken companion–most often a white dwarf.

"We know of a few other systems, called ultra-compact low-mass X-ray binaries, that are likely to be evolving according to the scenario above and may likely represent the progenitors of a pulsar like J1719-1438" said researcher Dr. Andrea Possenti, Director at INAF-Osservatorio Astronomico di Cagliari, Italy.

However, pulsar J1719-1438 and its companion are so close together that the companion can only be a very stripped-down white dwarf, one that has lost its outer layers and over 99.9 percent of its original mass.

"This remnant is likely to be largely carbon and oxygen, because a star made of lighter elements like hydrogen and helium would be too big to fit the measured orbiting times," said Dr. Michael Keith (CSIRO), one of the research team members.

The density means that this material is certain to be crystalline, meaning a large part of the star may be similar to a diamond.

"The ultimate fate of the binary is determined by the mass and orbital period of the donor star at the time of mass transfer. The rarity of millisecond pulsars with planet-mass companions means that producing such 'exotic planets' is the exception rather than the rule, and requires special circumstances," said Dr. Benjamin Stappers from the University of Manchester.

The team found pulsar J1719-1438 among almost 200,000 Gigabytes of data using special codes on supercomputers at Swinburne University of Technology in Australia, The University of Manchester in Britain, and the INAF-Osservatorio Astronomico di Cagliari, Italy.

The discovery was made during a systematic search for pulsars over the entire sky, which also involved the 100-meter Effelsberg radio telescope of the Max-Planck-Institute for Radioastronomy (MPIfR) in Germany.

"This is the largest and most sensitive survey of this type ever conducted. We expected to find exciting things, and it is great to see it happening. There is more to come!" said Professor Michael Kramer, Director at the MPIfR.

The discovery of the new binary system is of particular significance for Professor Bailes and fellow team member Professor Andrew Lyne, from The University of Manchester, who jointly ignited the entire pulsar-planet field in 1991 with what proved to an erroneous claim of the first extra-solar planet.  However, the next year the first extra-solar planetary system was discovered around the pulsar PSR B1257+12.

The findings are published online August 25 in the journal Science.


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