A star turned into a diamond

A companion star has lost its atmosphere and most of its mass to the pulsar it orbits, what remains is the core - an extinguished star the size and mass of a planet made of diamond

Tammy Plotner, Universe Today

Four thousand light years from us in the Serpent group there is a star with a heart that beats every few thousandths of a second. An international team of researchers from Australia, Germany, Italy, Great Britain and the USA, including Prof. Michael Kramer of the Max Planck Institute for Radio Astronomy in Bonn, Germany, are listening to it. They are using the 64-meter Parkes radio telescope in Australia. The companion star in the system is a low-mass white dwarf Very much, transformed into a planet made of pure diamond.

The density of the planet is at least that of platinum, and this provides us with a clue to its origin," says the head of the research team, Prof. Matthew Bayles from the Swinburne Institute of Technology in Australia. Bayles leads the "Dynamic Universe" team in a new wide-field astronomical initiative, the Center of Excellence for Astrophysics (CAASTRO ) who is currently on sabbatical at the Max Planck Institute for Radio Astronomy.

Like a lighthouse, J1719-PSR 1438 systematically emits radio signals around it. When the researchers noticed a specific modulation every 130 minutes, they realized it was a signature of planetary dimensions. Given the distance of its orbit, it is very likely that the companion is the core of what was once a massive star whose material was pulled by the pulsar's gravity.

"We know of very few other systems of this type, known as ultra-compact low-mass X-ray binaries, which may develop according to the above scenario and may represent the prototype of pulsars such as J1719-1438," said Dr. Andrea Fossanti of the IANF Observatory in Cagliari, Italy.

"When almost all of its original mass is gone, very little remains of the companion star for it to turn into carbon and oxygen - unless it is the core of a star that was previously active and managed to produce these cores, and therefore stars that are still rich in lighter elements such as hydrogen and helium will not fit into the equation. The star is so Compressed, until its material is more like a diamond.

The final fate of the binary system will be determined by the mass and orbital period of the donor star at the time of the mass transfer. The rarity of pulsars with a cycle time of milliseconds with a companion the size of a planet means that the production of "exotic planets" is the exception, and requires unique conditions," says Dr. Benjamin Steppers from the University of Manchester.

"The new discovery surprised us. But there are certainly many things to discover about the physics of pulsars in the coming years," concluded Michael Kramer.

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