Artist's concept of the pulsar and its planet. The system could fit into our Sun, represented by the yellow surface.
What’s the News: An international team of astronomers has found an exotic planet possibly made of diamond
, located about 4,000 light-years away from Earth. The researchers believe that the unusual planet was once a sun-like star, transformed into its current state by its hungry stellar companion, a millisecond pulsar
. How the Heck:
When a massive star dies in a supernova, it sometimes collapses into a pulsar, a highly compacted stellar corpse that emits periodic beams of electromagnetic radiation from its poles. If a pulsar is part of a binary system, it can feed on its nearby stellar friend and speed up its spin to hundreds of rotations per second, effectively becoming a millisecond pulsar. (About 30% of millisecond pulsars found are solitary—astronomers don't know how they formed.)
Astronomers detected the pulsar, known as PSR J1719-1438, during a large survey using the CSIRO Parkes Observatory near Sydney, Australia. When they studied the pulsar’s radio beams, they noticed slight variations in the signals, likely caused by the gravitational tug of an orbiting body. By analyzing this signal modulation, they were able to determine that the second object has a little more mass than Jupiter and revolves around the pulsar every two hours and ten minutes at a distance of about 600,000 kilometers (at its closest, Mercury is about 46 million km from the Sun).
But at this distance, a planet the size of Jupiter would be ripped apart by the intense gravity of J1719-1438. The researchers calculated that the planet could be no larger than 60,000 km in diameter, less than half the size of Jupiter, giving it a density about 18 times that of water (via National Geographic).
With the planet’s density and distance from the pulsar, the astronomers reasoned that the object was once a star itself—J1719-1438 siphoned matter from the surface of the star, stripping it of its outer layers of hydrogen and helium. This left a white dwarf—the core of a dead sun-sized star—that is made up of mostly carbon (with a bit of oxygen) and has only 0.1 percent of its original mass. Under the high pressure of the planet's own gravity, the carbon would crush into a crystalline form---that is, diamond. The team is unable to specify what percentage of the planet would be diamond, but they believe it's pretty high, according to TIME.
What’s the Context:
PSR J1719-1438 is one of only two millisecond pulsars found to have orbiting planets. The other, PSR B1257+12, has three planets, none of which are thought to be made of diamond.
Last year, there were reports of another “diamond planet.” This body, called WASP-12b, was the first planet found to have more carbon than oxygen in its atmosphere, leading astronomers to believe that its surface is rich in diamonds.
With better technology and techniques, astronomers have been finding extra-solar planets at an accelerated rate over the last few years. Some of the exoplanets are about as strange as the diamond planet, like the planet that reflects practically no incident light.
Reference: M. Bailes et al. Transformation of a Star into a Planet in a Millisecond Pulsar Binary. Science, 2011; DOI: 10.1126/science.1208890
Image courtesy of Swinburne Astronomy Productions