Burned-out star offers Whole Earth Telescope team insights into sun's future
June 6, 2011 - Judi Provencal, the University of Delaware astronomer, has been busy staffing the command center for a star watch of epic proportions, the latest observing run of the Whole Earth Telescope (WET). This global collaboration of observatories collects asteroseismic data—information on stellar waves that pass through hot stars in the cosmos like earthquakes pass through Earth—to determine what’s going on inside these exploding balls of hydrogen and helium gas.
Every day for the past six weeks, Provencal has encouraged faithful observers at 15 major telescopes in 11 countries, from Brazil to China, to focus their lenses on a handful of white dwarfs. These stars have used up all the fuel at their core and while they are still very hot, they are actually slowly cooling, a process that will take billions to trillions of years. Eventually, that’s what will happen to the sun, Provencal says.
The team’s primary target, GD358, is a white dwarf 120 light years away from Earth. Provencal has been studying it since she completed graduate school in 1994; her thesis adviser actually discovered the star.
“This star has changed a lot even since we started watching it several weeks ago,” notes Provencal, an assistant professor of physics and astronomy who directs the Delaware Asteroseismic Research Center (DARC). “It’s pulsating, or sloshing around, at new frequencies. Think of a pulsating star as a bell. If you have a bell and ring it, it makes a certain tone, but now suddenly it has a different tone. Well, what accounts for that? This is a challenge for the theorists.”
An astronomical relay team
Each participating observatory photographs the target star every 20 seconds throughout the night. As sunrise nears, the task is handed off to the next observatory where night has fallen, and so on. All of the images—hundreds of gigabytes of data—are transmitted daily to a computer in Provencal’s UD office.
The data is then transferred over the Internet to Mt. Cuba Astronomical Observatory in Greenville, Del., where it is reduced using software written by UD doctoral student James Dalessio. The observatory and the Crystal Trust are supporting the research.
“From all these images, we’ll pull out how many photons of light are coming from the star in a plot called a light curve,” Provencal says. The light curves are posted on the DARC website every day so the observers can see the data as the run proceeds.
“The star gets brighter and dimmer every 10 minutes because it is pulsating,” she explains. “The peaks in the light curve represent when the star is pulsating outward. From these data, we can determine the frequency of the pulsations, and theoretical physicists like my colleague Mike Montgomery at the University of Texas at Austin can tell us what is happening inside the star.”
After all of the number crunching and analysis, the research team will report their findings in a scientific paper. Generally, it is ready for publication about a year after an observing run, Provencal says.
One question Provencal hopes to answer is whether or not GD358 has a magnetic cycle, meaning that a magnetic field will tug on one side of the star and cause a shift in its rotation every so many years.
“We don’t understand why the sun has a magnetic field, although only a weak one,” she notes. “We’re trying to confirm that this star is similar to what the sun will become in about 4 billion years.”
One of WET’s secondary targets, a star called KIC10139564, more than 300 light years away (the equivalent of more than a quadrillion miles), also is being watched by NASA’s Kepler satellite. Yet no one has compared the satellite’s timings to see how good its clock is, Provencal says. The WET team’s data will help with the evaluation.
When WET started in 1980, having as many as eight telescopes on a run was an achievement, but under Provencal, more than double that number now participate. Her enthusiasm is infectious.
“We’re all interested in the science and get along really well,” she notes. “It’s also just plain fun.”
The team’s good humor and dedication continually impress Provencal.
She points out that a student from Poland with an injured foot is manning a telescope in Croatia, and that the robotic telescope at Mt. Lemmon in Arizona is being remotely operated by scientists in South Korea. And there’s still snow at Russia’s Peak Terskol Observatory at an elevation of 10,000 feet in the Caucasus Mountains. Aleksandr Sergeev, the observer there, has two cats to keep him company.
“He says the cats ‘sweep away the clouds,’” Provencal says, grinning.
When Provencal needs to clear her mind in the midst of such a long observing run, she goes horseback riding. Are her horses named “Star” or perhaps “Comet”?
“No,” Provencal says, “but I do have a cat named ‘Sparkles.’”