Whole Earth Telescope Confirms Gem Of A Star

Steve Kawaler, professor of physics and astronomy, directs the astronomy consortium known as the Whole Earth Telescope (WET), which is funded in part by the National Science Foundation. The group’s goal is to obtain uninterrupted observations of distinctive stars for days at a time. In this case, the WET trained its telescopes on the pulsating white dwarf star BPM37093, or “Diamond Star,” back in 1998 and 1999. WET astronomers monitored it from observatories in South Africa, Brazil, Chile, New Zealand and Australia, obtaining more than 400 hours of data on the star’s subtle brightness variations.

During these runs, the Hubble Space Telescope (HST) also was observing the star. The overall process was coordinated at WET headquarters at Iowa State University.

The scientists measured the vibration frequencies of this slowly cooling remnant of a star (a white dwarf star is the final remnant of stars like our Sun, which has exhausted its nuclear fuel; it is mostly the ash of carbon and oxygen remaining). To listen to how this pulsating star might sound if its frequencies were accelerated, go to http://wet.physics.iastate.edu/Audio/

Astronomers can determine the structure of the star’s interior through the technique of asteroseismology. This process is similar to the terrestrial seismology that provides views of the Earth’s interior. The WET observations have revealed BPM30793’s interior; following several years of analysis, it has been determined that the star’s core is indeed mostly crystalline.

"I can’t begin to describe the dedication of the WET astronomers to their work,” Kawaler said. “Many spent countless hours on cold mountaintops around the world with little to show for it but numbers and graphs. After several years of analysis, though, their work has provided the data needed to show that some stars are indeed mostly crystalline.”

The preliminary interpretation of these results has been submitted for publication in the Astrophysical Journal Letters, in an article authored by WET astronomers from Harvard University, Britain’s University of Cambridge and Brazil’s Universidade Federal de Santa Catarina. Brazilian scientist Antonio Kanaan, who was the first to find that BM37093 vibrates, and the rest of the WET team are completing a more extensive analysis of the data obtained from the WET and HST observations.

The “Diamond Star” is located 50 light years from Earth in the constellation Centaurus. (A light year is the distance light travels in a year, about 6 trillion miles.) The star measures 2,500 miles across and has a mass corresponding to 5 million trillion trillion pounds, or 10 billion trillion trillion carats. To date, the largest diamond on Earth has been the 530-carat Star of Africa, cut from a 3,100-carat diamond discovered in 1905.

Finding a crystalline star can be considered a breakthrough, but calling it a diamond may still be wishful thinking.

“Travis Metcalfe [the Harvard researcher who co-authored the journal article] and his co-workers indeed showed that BPM37093 is crystalline, but we can’t distinguish between crystalline carbon or oxygen yet, much to my wife’s dismay,” Kawaler said. “So, while it may be a huge carbon crystal, it may also be a huge oxygen crystal – or one giant impurity!”