The planet is about five times the diameter of the Earth, and circles the dead star of about 12-miles in diameter every two hours and 10 minutes.
The dead star, known as a pulsar, itself spins around 10,000 times a minute.
The discovery was made by a team of astronomers located in Australia, Europe and the United States, and they're reporting their finding Thursday in the journal Science.
They found the system because pulsars give off radio signals as they spin and every time the beam passes by Earth, radio telescopes can pick it up the signal.
The newly discovered pulsar in this system is in the constellation Serpens (the Snake) and given the unromantic name PSR-J1719-1438. It is located between Earth and the center of the Milky Way galaxy.
The Parkes radio telescope in Australia picked up the signal first, then the Lovell telescope at the Jodrell Bank Observatory in England and the Keck in Hawaii confirmed the finding.
Astronomers noted that the signals were modulated, which meant there was something else out there with the pulsar. They concluded it was a small planet, a white dwarf.
The told them several things about the planet. It was flying at 310 miles per second and was 370,000 miles from the pulsar, a little less than the radius of our sun.
Mathew Bailes of Swinburne University of Technology in Melbourne, Australia, said small as the planet is, it has a mass 1.4 times that of our sun. The density--23 times the density of water-- indicated it was made up mainly of oxygen and carbon, not the usual helium and hydrogen found in stars.
Additionally, it means the planet is crystalline in form. That defines a diamond.
That such an object could exist was predicted in 2001 by Krishna Rajagopal and Nobel Laureate Frank Wilczek. They called it "a diamond as big as the Ritz, actually much bigger, and a million billion time as dense."
It would not look like a diamond out there. Bailes said the weather prevented them from getting a good view, but his guess is that one side would be lit up to about 10,000 degrees Fahrenheit with a slightly reddish glow.
"We don't know the atmosphere or what the temperature gradient would be from the bright side to the dark side," he said from the Max Plank Institute in Bonn, Germany where he is on sabbatical. The dark side would emit infra-red.
If you chipped off a piece would you have a diamond in your hand?
"There's a good chance of that," he said. "If you could grab big chunks and bring it home you could turn it into a pretty useful diamond."