A white dwarf star, the coldest and dimmest ever found, has been discovered. This carbon-rich stellar body is so cold, it has formed a diamond in space the size of the Earth. Surface temperatures of just 4,900 degrees Fahrenheit may seem hot in terrestrial terms, but is frigid in stellar terms. Our own sun has a surface temperature of nearly 10,000 degrees Fahrenheit.
White dwarfs are the collapsed remnants of stars roughly the mass of our own sun. They are approximately the size of our home planet, and composed mostly of carbon and oxygen. The stellar corpses slowly dim over time, and astronomers believe this body is around 11 billion years old, roughly the same age as the Milky Way.
This giant diamond in space was discovered using a series of radio observatories, including the Green Bank Telescope (GBT) and the Very Long Baseline Array (VLBA). It lies 870 light years from Earth, in the direction of the constellation Aquarius.
It is a member of a binary system, paired with a pulsar, named PSR J2222-0137. These bodies are another type of stellar remnant, called neutron stars, the remains of stars more massive than our sun. Pulsars spin at incredible rates, and produce electromagnetic beams that can be directed toward the Earth. This pulsar was discovered before the companion, using the GBT, and measured to be spinning 30 times every second. Astronomers calculated the body had an unseen companion, which was theorized could be a super-cool white dwarf.
"It's a really remarkable object. These things should be out there, but because they are so dim they are very hard to find," David Kaplan from the University of Wisconsin-Milwaukee, said.
Adam Deller, an astronomer at the Netherlands Institute for Radio Astronomy (ASTRON), studied the system for two years, sing the VLBA.
Investigation of signals from the pair were used to measure warping of space caused by the system. This effect, like waves in water from a pair of twirling bathers, was first predicted by Albert Einstein. These ripples in space-time cause a delay in signals from the pulsar, when it is on the "far" side of the waves. This effect was used to calculate masses of the dead stars with great precision. The white dwarf was found to have a mass five percent greater than our sun, and the pulsar was found to be 20 percent more massive than our companion star.
"The recycled pulsar PSR J2222-0137 is one of the closest known neutron stars," researchers wrote in an article, announcing the results of their study, published in Astrophysical Journal.
Measurements of the distance to the pulsar is believed to be the most accurate ever made.
Investigation of the pulsar/white dwarf pair is detailed on the Cornell University Library Web site.