Nine hundred light years away in the direction of the constellation Aquarius resides a recently discovered dwarf star that is so cold its carbon has crystallized – much like a diamond.
At first scientists were looking at a pulsar that was spinning 30 times a second and gravitationally bound to another object. But as they observed this for over two years they came to realize that the companion object wasn’t another neutron star as they suspected: it was an 11-billion-year-old dwarf star that was uncommonly cold.
White dwarfs are end-state stars that have collapsed to form hot, extremely dense, planet sized objects. They’re composed mainly of carbon and oxygen and can be as massive as the sun; however, they’re often the size of our own Earth. After these stars use up all their nuclear fuel they slowly cool and fade over billions of years. It’s a process that our own sun could possibly face.
Combining the the Green Bank Telescope in West Virginia and the Very Long Baseline Array at Mauna Kea, a team lead by David Kaplan at the University of Wisconsin-Milwaukee were able to study how the gravity of the pulsar’s companion warped space and caused delays in the radio signal. They concluded that the pulsar had a mass 1.2 times that of the sun and its companion was 1.05 times the sun. They then concluded that the orbits were too orderly for a second supernova to have taken place.
Bart Dunlap from the University of North Carolina at Chapel Hill explains that “our final image should show us a companion 100 times fainter than any other white dwarf orbiting a neutron star and about 10 times fainter than any known white dwarf, but we don’t see a thing. If there’s a white dwarf there, and there almost certainly is, it must be extremely cold.”
This white dwarf star couldn’t be more than 2,700 degrees Celsius; compared to our sun, its center is over 5,000 times hotter. Scientists believe that such an ancient star should only have remnants of largely crystallized carbon: yes, an Earth-sized diamond.