Whole Earth Telescope Trains Its Sights On Two Strange Star Systems

The astronomical objects of their desire: BPM37093, a white dwarf star thought to be largely solid; and PG1336-018, a tightly bound interacting binary star system that has caught astronomer's eyes.

"PG1336-018 produces the sexiest light curve in astronomy," said Steve Kawaler, an Iowa State astronomer.

To make critical measurements of these stars, Kawaler's group is using a modern-day armada of Earth-based telescopes, which make up the Whole Earth Telescope. WET telescopes in South Africa, Chile, Australia, Poland, Spain, Israel, China and India are among those being used in the observations, which began April 7 and will continue until April 22.

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. Assisting in WET headquarters is Dave Kilkenny, an astronomer from South Africa who discovered one of the stars, and Atsuko Nitta, a University of Texas student who heads up the team observing the other star.

The current observation run of 18 observatories is the largest run by WET on any object. In addition to WET observations of BPM37093, the orbiting Hubble Space Telescope will turn its sights on the star on April 13 and 14.

Solid star A WET observation run of BPM37093 last year teased astronomers with hints of its composition. The star is 17 light-years from Earth (a light year is the distance light travels in a year, about 6 trillion miles) and located in the constellation of Centaurus.

Last year, Kawaler thought the star might consist of a diamond type material of crystallized carbon and oxygen. He now says it is much more likely to be made up of "an entirely new material we've never seen before."

The team hopes to get all of the data it needs to confirm that the star is in fact solid. The astronomers will be measuring the vibration frequency of BPM37093 with stellar seismological techniques to ascertain its makeup. These observations could confirm a 30-year-old theory -- that white dwarf stars, the slowly cooling remnants of stars like our Sun, may have condensed into solid or partially solid stars.

Crystallized white dwarf stars have been theorized to exist for years, but because these stars are rare and exist under very extreme conditions, proving their existence has been a challenge. 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. The only other known partially solid stars are neutron stars.

"Here on Earth, we will never be able to experience the types of pressures on the interiors of these stars," Kawaler said. "We expect that these measurements will prove or disprove that such solid stars do in fact exist."

Sexy light curve The other object WET astronomers will be measuring is designated PG1336-018. It is about 2,000 light years from Earth and is in the constellation of Virgo. An interesting aspect of this object is its incredibly rapid orbital rotation with one of the two stars pulsating much like BPM37093.

Kawaler explained that PG1336-018 is a tightly bound interacting binary star system where one star is bright and the other faint. Both are roughly the size of Jupiter, the largest planet in the solar system. PG1336-018's orbital rotation (how long it takes for the stars to rotate about each other) is a swift 2.6 hours. By comparison, it takes Earth one year to orbit about the Sun and Mercury 88 days to complete its solar orbit.

The incredibly rapid orbit of these two stars can provide clues as to their physical makeup, Kawaler said. As the two stars spin about each other they are continually eclipsing each other. As they do that, astronomers can learn clues about the composition of these two stars.

For example, as the bright star goes behind the faint star, astronomers can use the faint star's blockage of light to check for variations in brightness across the face of the bright star. That piece of information will give astronomers clues as to how the bright star is vibrating.

"This system is miraculous in that the two stars, separated by no more than the distance of the Earth to the moon, complete their orbit so quickly," Kawaler said. "But the best part is the brighter of the two is a pulsating star, so we can peek into its insides and see what makes it tick."

Kawaler added that while each observation is as unique as its subject, both will help astronomers get a handle on the age of the universe.

The measurements of GP1336-018, the binary star system, has implications to the distance and age of globular clusters, which are the oldest collections of stars in our galaxy. More precise calibrations of the distances between these globular clusters can help astronomers hone their caluclations on the age of the entire observable universe.

Likewise for BPM37093, the potential solid star, comparing new WET data to existing models of the evolution of such stars, astronomers can better understand how long it takes for these objects to reach latter stages of stellar evolution. This information will help determine if current estimates of the age of the universe, currently thought to be about 9 billion years, is accurate or if the universe is actually much older.

"Nature kindly provided us with stars that vibrate, and if we can read the vibrations correctly, we can tell about their insides -- what they are now and what they were like in the past," Kawaler explained. "Since our Sun will eventually become a star like these, it is a glimpse into the distant future of what will become of our own star."

The Whole Earth Telescope is a program of the International Institute of Theoretical and Applied Physics (IITAP). IITAP is collaboration between Iowa State University and the United Nations Educational, Scientific and Cultural Organization (UNESCO).