Iowa State University

Inside Iowa State
Apr. 03, 1998

In search of a big diamond

by Skip Derra

Steve Kawaler aims his telescopesnot to the far reaches of the universe, but to objects much closer and much more interesting. From April 20 to May 2, Kawaler, a professor of physics and astronomy, will lead a group of about 50 astronomers in an observation of a "particularly interesting" pulsating white dwarf.

The white dwarf star, designated BPM37093, is the slowly cooling remnant of a star once nearly the size of our Sun. It resides only 17 light-years from Earth in the constellation of Centaurus. Astronomers are interested in BPM37093 for several reasons.

Learning more about white dwarfs could help them better determine the age of our galaxy and the universe. Understanding the properties of white dwarf stars is important because all stars, depending on their size, will become either eternally cooling dwarf stars or fiery exploding supernovas.

Being a white dwarf star, Kawaler said, BPM37093 has burned its gaseous fuel and all that remains is ash of carbon and oxygen. By measuring the frequency of pulsations emanating from BPM37093, astronomers can sneak a peak into its interior. Kawaler thinks what they'll find could be a gemologist's dream.

"We think it's primarily made up of crystallized carbon with an oxygen impurity," he said. "That would make it a diamond with a blue-green tint. Its estimated carat weight is 1034, or 10 billion trillion trillion. This could truly be a diamond in the sky."

Scientists have theorized the existence of crystallized stars for 30 years. But there has never been direct proof. To make the first direct measurements of the star, Kawaler's group will use a modern-day armada of Earth-based telescopes coupled with highly sensitive measurements from the orbiting Hubble space telescope.

The astronomers will use some observatories of the Whole Earth Telescope (WET) to monitor BPM37093 from Earth. WET telescopes in South Africa, Brazil, Chile, New Zealand and Australia will be used in the observation.

Kawaler is the director of WET, which includes a total of 22 observatories around Earth and allows 24-hour monitoring of objects. WET is headquartered at Iowa State and is a program of the International Institute for Theoretical and Applied Physics.

The core observation will be run April 20-29. During this time, the Hubble space telescope will turn its attention to BPM37093 and provide the astronomers with measurements in ultraviolet and optical wavelengths. Kawaler said the Hubble measurements will allow the astronomers to actually see BPM37093 as it pulsates.

The astronomers will continue to monitor the dwarf star periodically for several years. What they'd like to obtain is the first direct evidence of a star that shines, or in this case, pulsates, like a diamond.

While the astronomers want to know what BPM37093 is made of, they also hope to pin down how the crystallization happens and determine if it is "a solid diamond or a diamond shell," Kawaler said.

"The material that is crystallizing is a mixture of different elements," he explained. "Different elements crystallize at different temperatures. Heavier elements like oxygen crystallize first, then the carbon will crystallize. If oxygen crystallizes in a gas of carbon, then those crystalline nuggets will sink to the inside of the star -- as if it were snowing."

The snowing effect would create additional energy not accounted for in current white dwarf star models, Kawaler said. "But if the oxygen crystallizes and stays suspended, then you're getting crystallization without an additional energy source. If it snows, you'll have an oxygen crystal core and a carbon crystal mantle. Sort of a diamond shell."

And if they detect a shell with snow, then cool white dwarf stars (the oldest stars in this part of the galaxy) are older than previously thought.

A pulsating white dwarf star that is snowing inside will be roughly 11 to 12 billion years old, rather than the currently estimated 9 billion years, Kawaler said. This finding will extend the lower limit of the age of the galaxy, and in turn extend the estimated age of the universe.

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