They say diamonds are forever. Perhaps it is closer to a billion years.

That is roughly the age of a white dwarf star, named BPM-37093, which Iowa State astrophysicist Steve Kawaler is studying.

What makes this star interesting is that it may be composed largely of crystalline carbon, something akin to a massive diamond.

In the early 1960s, Dr. Ed Salpeter, a professor of physics at Cornell University, proposed a theory that matter solidifies inside some white dwarf stars, Kawaler said.

“What [he] said was that when a star becomes a white dwarf star it collapses, the density grows and at some point the nuclei of the atoms inside the star get close enough together to feel a repulsive force from one another which locks them into a solid structure,” Kawaler said. “It is the way anything solidifies.”

Kawaler said it has been difficult to test this theory until recently.

“The densities in these stars are so high that it’s completely unattainable in any earth-based laboratory,” Kawaler said.

The discovery that BPM-37093, some 17 light years from earth, is a pulsating star and has sufficient mass to be a star with a possible crystalline interior excited scientists, Kawaler said.

“We could use the pulsations to probe the inside of the star,” he said. “The signature of the light variations would be different if the star was solid inside or gaseous inside.”

Kawaler said he examined the white dwarf star using what is called a “whole earth telescope.” This method uses several telescopes on different parts of the earth to observe a star or other astronomical body. The network of telescopes is coordinated to work as one telescope.

“We had observers in South America, South Africa, New Zealand and Australia,” Kawaler said. “This allowed us to observe the star 24 hours a day. When the star would set for our observer in Chile, it would be rising for our observer in New Zealand, and as it set in New Zealand, our observer in South Africa would begin to observe it.

“This way we could hand it off in a sort of global relay for a couple of days. The whole earth telescope was the instrument that we needed to use to measure these oscillations and then compare them with theory,” Kawaler said.

If the light from this star was not oscillating, it would be hard to distinguish it from any other star of similar mass and brightness, Kawaler said. The oscillations are very small — only a fraction of what the human eye can detect. The whole earth telescope was necessary to get enough light to detect them.

Kawaler said he and 50 of his collaborators are still busy analyzing the data they collected on BPM-37093.

If the structure of the star turns out not to be crystalline, this will be exciting for scientists, Kawaler said. It will suggest that another theory needs to be developed to explain the physical structure of these white dwarf stars.

If the star is composed of crystalline carbon, Kawaler said it is unlikely to be a diamond structure in the way we think of it on earth.

“Diamond is a very special crystalline form of carbon,” he said. “This star will be crystalline and it will be carbon, but it is probably going to be too hot to make a very good diamond.

“It is certainly exotic stuff, whether it is diamond or not,” Kawaler said. “Chances are it is not diamond but some other crystalline form of carbon that we just have no experience with.”

Dr. Douglas Finnemore, chair of the Department of Physics and Astronomy at ISU, is skeptical that the structure of the carbon in this star is anything like a diamond.

“The diamond structure does not occur very often in nature,” Finnemore said. “There is a difference between the carbon in these stars and the carbon in a diamond ring. What most people mean by a diamond just simply doesn’t apply to these stars.”

Whatever the structure of the white dwarf star, it is not something that prospecting astronauts could mine and bring back to earth.

Kawaler said even if you could get to the star and elude the destructive gravitational forces and intense heat, you could not remove a handful of the star and take it with you. The star’s special structure depends on gravity.

“When you remove it from the gravitational field of the white dwarf, there is nothing to keep it together, so it would probably explode,” Kawaler said. “It’s pretty safely insulated from people going there and grabbing some.”