Allo, allo? A star is ringing

Dec 21, 2005
Alpha Centauri and the Southern Cross

Astronomers have used ESO's Very Large Telescope in Chile and the Anglo-Australian Telescope in eastern Australia as a 'stellar stethoscope' to listen to the internal rumblings of a nearby star. The data collected with the VLT have a precision better than 1.5 cm/s, or less than 0.06 km per hour!

Image: Alpha Centauri and the Southern Cross.

By observing the star with two telescopes at the same time, the astronomers have made the most precise and detailed measurements to date of pulsations in a star similar to our Sun. They measured the rate at which the star's surface is pulsing in and out, giving clues to the density, temperature, chemical composition and rotation of its inner layers - information that could not be obtained in any other way.

The astronomers from Denmark, Australia, and the USA [1] used Kueyen, one of the four 8.2-m Unit Telescopes of ESO's Very Large Telescope (VLT) at Cerro Paranal in Chile, and the 3.9-m Anglo-Australian Telescope (AAT) in New South Wales (Australia), to study the star Alpha Centauri B, one of our closest neighbours in space, about 4.3 light-years away.

Alpha Centauri is the brighter of the two 'Pointers' to the Southern Cross. Alpha Centauri itself is a triple system and Alpha Centauri B is an orange star, a little cooler and a little less massive than the Sun.

Churning gas in the star's outer layers creates low-frequency sound waves that bounce around the inside of the star, causing it to ring like a bell. This makes the star's surface pulsate in and out by very tiny amounts - only a dozen metres or so every four minutes [2]. Astronomers can detect these changes by measuring the small, associated wavelength shifts.

The researchers sampled the light from Alpha Centauri B for seven nights in a row, making more than 5 000 observations in all. At the VLT, 3379 spectra were obtained with typical exposure times of 4 seconds and a median cadence of one exposure every 32 seconds! At the AAT 1642 spectra were collected, with typical exposures of 10 s, taken every 90 s.

"From this unique dataset, we were able to determine as many as 37 different patterns (or modes) of oscillation", says Hans Kjeldsen, from University of Aarhus (Denmark) and lead author of the paper describing the results [3].

The astronomers also measured the mode lifetimes (how long the oscillations last), the frequencies of the modes, and their amplitudes (how far the surface of the star moves in and out). Such measurements are a huge technical challenge. Indeed, the star' surface moves slowly, at the tortoise-like speed of 9 cm a second, or about 300 metre an hour. The astronomers borrowed their high-precision measurement technique from the planet-hunters, who also look for slight Doppler shifts in starlight.

"So much of what we think we know about the universe rests on the ages and properties of stars," said Tim Bedding, from the University of Sydney and co-author of the study. "But there is still a great deal we don't know about them."

By using two telescopes at different sites the astronomers were able to observe the Alpha Centauri B as continuously as possible.

"That's a huge advantage, because gaps in the data introduce ambiguity," said Bedding. "The success of the observations also depended on the very stable spectrographs attached to the two telescopes -- UVES at the VLT and UCLES at the AAT -- which analysed the star's light."

Source: ESO

Explore further: Far from home: Wayward cluster is both tiny and distant

add to favorites email to friend print save as pdf

Related Stories

What's happening in the universe right now?

Jan 30, 2015

There are some topics that get a little frustrating in their pedantry, but can really draw attention to the grand scope and mechanics in our Universe. This is definitely one of them.

Image: Multicoloured view of supernova remnant

Dec 22, 2014

Most celestial events unfold over thousands of years or more, making it impossible to follow their evolution on human timescales. Supernovas are notable exceptions, the powerful stellar explosions that make ...

What is the Smallest Star?

Dec 05, 2014

Space and astronomy is always flaunting its size issues. Biggest star, hugest nebula, prettiest most talented massive galaxy, most infinite universe, and which comet came out on top in the bikini category. ...

Earth-sized planet found just outside solar system

Oct 16, 2012

(Phys.org)—European astronomers have discovered a planet with about the mass of the Earth orbiting a star in the Alpha Centauri system—the nearest to Earth. It is also the lightest exoplanet ever discovered ...

Recommended for you

Image: Training for Sentinel-2A launch

58 minutes ago

On 25 February, the Sentinel-2A Mission Control Team at ESOC, ESA's mission operations centre, Darmstadt, Germany, commenced simulation training for the critical launch and early orbit phase.

Far from home: Wayward cluster is both tiny and distant

17 hours ago

Like the lost little puppy that wanders too far from home, astronomers have found an unusually small and distant group of stars that seems oddly out of place. The cluster, made of only a handful of stars, ...

Why don't we search for different life?

21 hours ago

If we really want to find life on other worlds, why do we keep looking for life based on carbon and water? Why don't we look for the stuff that's really different?

OSIRIS catches glimpse of Rosetta's shadow

22 hours ago

Several days after Rosetta's close flyby of comet 67P/Churyumov-Gerasimenko on 14 February 2015, images taken on this day by OSIRIS, the scientific imaging system on board, have now been downlinked to Earth. ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.