Iowa State University

April 20, 1998


AMES, Iowa -- A team of about 50 astronomers will train their telescopes on a relatively close pulsating white dwarf star for the next three weeks with the goal of possibly finding a true gem in the sky. The astronomers, led by Steve Kawaler, an Iowa State University professor of physics and astronomy, will be monitoring a vibrating white dwarf star designated BPM37093, which is 17 light years from Earth. (A light year is the distance light travels in a year, about 6 trillion miles).

The astronomers will make their observations using the Whole Earth Telescope and the Hubble Space Telescope from April 17 to May 4. Their findings could have an impact on the age of our galaxy and of the universe, and become the delight of gemologists worldwide.

"We think BPM37093 is primarily made up of carbon and oxygen in a crystallized state," Kawaler says. "That would make it a diamond with a blue-green tint. It's estimated carat weight is 1034, or 10 billion trillion trillion. This truly could be a diamond in the sky."

BPM37093 is a slowly cooling remnant of a star that once was a little more massive than our Sun. It resides in the constellation of Centaurus and is clearly viewable only from the Southern Hemisphere. Understanding the properties of white dwarf stars is important because nearly all stars will become eternally cooling white dwarf stars. Only the most massive stars will become fiery exploding supernovas.

Being a white dwarf star, Kawaler said, BPM37093 has burned its nuclear fuel and all that remains is ash of carbon and oxygen. The only other known partially solid stars are neutron stars.

By measuring the vibration frequency of BPM37093, astronomers can sneak a peak into its interior. Through stellar seismological techniques, Kawaler and the team of astronomers will attempt to ascertain the makeup of BPM37093.

"The pulsations will tell us what's going on inside a star the same way earthquakes tell us about the inside of Earth," Kawaler said. "Each of the white dwarf's various brightness changes tells us something unique about the star's interior. It is very much like being able to hear and identify a violin and a bassoon in an orchestra concert."

Crystallized white dwarf stars have been theorized to exist for 30 years, but because these stars are rare and exist under very extreme conditions, proving their existence has been a challenge.

"Here on Earth, we will never be able to experience the types of pressures on the interiors of these stars," Kawaler said. "It's been a theory for 30 years, but it never has been tested. A white dwarf is a very, very dense star. One teaspoon of matter from these stars weigh as much as the New York Yankee infield -- about 500,000 grams."

To make the critical measurements of the star, Kawaler's group will use a modern-day armada of Earth-based telescopes, which are part of the Whole Earth Telescope (WET). WET telescopes in South Africa, Brazil, Chile, New Zealand and Australia will be used in the observations. These measurements will be coupled with highly sensitive measurements from the orbiting Hubble Space Telescope.

Kawaler is director of WET, which has partners at 22 observatories around Earth and allows 24-hour monitoring of stars. WET is headquartered at Iowa State University and is a program of the International Institute of Theoretical and Applied Physics.

The core observation run will be April 20-29. During this time, the Hubble Space Telescope will turn its attention to BPM37093 and provide the astronomers with highly sensitive measurements in ultraviolet and optical wavelengths. Kawaler says the Hubble will allow astronomers to determine the precise pattern of vibrations on BPM37093, while the WET observations will provide the precise timing of the vibrations.

The astronomers plan to continue to monitor the white dwarf star periodically for several years. They also hope to pin down how the crystallization happens and determine if BPM37093 is a "solid diamond or a diamond shell with oxygen snow," Kawaler said.

"The material that is crystallizing is a mixture of different elements," Kawaler 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 may sink to the center of the star -- as if it were snowing."

The snowing effect would create additional energy not accounted for in some 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 crystalline core and a carbon crystal mantle. Sort of a diamond shell."

And if the astronomers 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 Milky Way galaxy and, in turn, extend the estimated age of the universe.

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