Skip to navigation | Skip to content

Stars' twinkle reveals their character

Surface of Sun taken by STEREO spacecraft

The changes in light levels provide a quick and relatively reliable way to determine a star's evolutionary state (Source: NASA/STEREO/Naval Research Laboratory)

Star tunes In 1806, English poet Jane Taylor famously lamented that a little star's twinkle left her wondering what it was.

Fast-forward 207 years and a new analysis of starlight collected by NASA's Kepler space telescope shows patterns in the flicker that are directly tied to the amount of boiling taking place on a star's surface, a key indicator of its size, mass and evolutionary state.

That information, in turn, reveals volumes about any orbiting planets, including those fortuitously positioned from their parent stars for liquid surface water, apparently a key ingredient for life.

"Everything you know about planets is tied to what you know about the host star," says Fabienne Bastien, an astronomy graduate student at Vanderbilt University.

"We don't observe the planets directly. We observe the stars and the influence that the planets have on their stars. So in order to make any conclusions about the size of the planet or the mass of the planet as it's pulling on the star when it's moving, you need to know the size and the mass of the star very well."

"That directly impacts whether or not you can claim that you have an Earth-like planet," she says.

Bastien, who is working on a doctoral dissertation, was analysing archived Kepler data for a totally different reason when she and colleagues chanced upon strange patterns in the data that they didn't understand.

"It was a complete surprise," says Bastien.

Boiling surfaces

It turns out the pattern provides a quick and relatively reliable way to determine a star's evolutionary state.

Stars like the Sun, which is about 4.6 billion years old, eventually will evolve into red giants as they run out of fuel for nuclear fusion. The new study shows the surfaces of younger dwarf stars boiling more vigorously than older giants.

"What we are looking at here is the gravitational acceleration in the stellar outer layers, what we often call the atmosphere," says astronomer Joergen Christensen-Dalsgaard, with Aarhus University in Denmark.

"The typical methods used have uncertainties up to 150 per cent. That very imprecise method is the easiest to do, and especially if you're dealing with 150,000 stars and you need to characterise them all, that's what you go to because it takes the least amount of resources. Our technique lets us beat that down to 25 per cent, which is very, very good for this field," added Bastien.

Kepler, which collected data from about 120,000 target stars between May 2009 and May 2013, was designed to search for Earth-like planets in stars' habitable zones,

For Bastien's study, which appears in this week's edition of Nature, astronomers analysed a few thousand stars in the Kepler data archive.

"If you have a large enough sample, then you start to pick out patterns in the way stars of different evolutionary states behave," she says.

While the study is based on eight-hour flicker patterns in the visible light coming from target stars, scientists translated the data into corresponding audio wavelengths, a poignant conceptualisation that no doubt would have intrigued, and delighted, poet Taylor.

Tags: astronomy-space, stars