- Planet detected orbiting a pulsar 4,000 light-years away
- It’s actually the remnant core of what was once a star
- Probably made of compressed carbon—diamond!
ASTRONOMERS USING ‘THE DISH’—CSIRO’s radio telescope near Parkes, NSW—believe they’ve found a small planet made of diamond, orbiting an unusual star.
The discovery was made by an international research team, led by Professor Matthew Bailes of Swinburne University of Technology in Melbourne, Australia, and is reported today in the journal Science.
“Although bizarre, this planet is evidence that we’ve got the right understanding of how these binary systems evolve,” said Dr Michael Keith of CSIRO Astronomy and Space Science, one of the research team members.
Not fitting the pattern
The researchers, from Australia, Germany, Italy, the UK and the USA, first found an unusual star called a pulsar, now named PSR J1719-1438, using the 64-m Parkes radio telescope in eastern Australia.
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.
The researchers followed up their discovery with the Lovell radio telescope in the UK and one of the Keck telescopes in Hawaii, and noticed that the arrival times of the pulsar’s pulses were systematically altered—in a way that must be caused by the gravitational pull of a small planet orbiting the pulsar.
Small, heavy and fast
The modulations of the radio pulses reveal 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.
A stripped-down dwarf
“This high density of the planet provides a clue to its origin,” Professor Bailes said.
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.
But pulsar J1719-1438 and its companion are so close together that the companion can only be a very stripped-down ‘white dwarf’ star, one that has lost its outer layers and over 99.9 per cent 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 orbit,” said CSIRO’s Dr Keith.
The density means that this material is certain to be crystalline—that is, a large part of the star may be similar to a diamond.
The pulsar and its planet 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.
Diamond planet Easy Q&A
What have they found?
- They’ve spotted a system that comprises a weird kind of star, called a pulsar, and a medium-sized planet that is probably made of almost pure carbon…which is most likely in the form of diamond or a diamond-like substance.
- The system is 4,000 light-years from Earth—that’s 40 thousand trillion kilometres away!
- The pulsar emits radio waves in a regular pattern as it spins, like a lighthouse, which is what the CSIRO’s Parkes radio telescope picked up.
- The planet itself cannot be seen as it is too small and too far away.
If they can’t see the planet, how do they know it’s really there?
- Its presence is inferred by the distorting effect it has on the pulsar’s powerful radio emissions.
- It whizzes around its star in just two hours (compared to one year for Earth around the Sun).
- The data was analysed using an incredible supercomputer at Swinburne University in Melbourne.
- The planet is about 5 times as wide as the Earth, but much, much heavier.
So why do they think it is made of diamond?
- Now here’s the interesting bit, because the planet actually seems to be the dense, remnant core of a star, rather than a traditional planet.
- Many stars, as they burn up their hydrogen fuel, end up having cores made of carbon.
- The star changed into a planet, with only it’s core remaining.
How did it change from a star into a planet?
- Because the pulsar has a huge gravitational pull and is a cosmic cannibal!
- The pulsar and the other star would have been orbiting very close to each other.
- The pulsar would have pulled all the outer gas layers off the other star—99.9 percent of its mass—eventually leaving it with just its carbon core.
- If we could have seen it happening, it would have looked like a huge whirlpool of gas coming off the doomed star and spiralling onto the neighbouring pulsar.
What do astronomers hope to learn from these types of star systems?
- For one thing, pulsars are the “end points”—the dying stages—in the lives of many kinds of big stars, so learning more about them tells us about the evolution and life cycle of those stars and the wider universe.
- But pulsars also are important for understanding and testing laws of physics.
- Astronomers can use them as “natural laboratories” for testing theories, such as Einstein’s theory of gravity.
- That’s because you can only go so far testing some theories in the laboratory—to really put them to the test, you need to study massive objects travelling at high speed, and that’s what pulsar systems are.
Main text adapted from information issued by CSIRO. Q&A by Jonathan Nally, SpaceInfo.com.au Images courtesy Swinburne Astronomy Productions and David McClenaghan, CSIRO.
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