Researchers measure the inner structure of distant suns from their pulsations

January 3, 2018, Max Planck Society
A glimpse into the heart: Artist's impression of the interior of the star, which was studied through its surface oscillations. Credit: Earl Bellinger / ESA

At first glance, it would seem to be impossible to look inside a star. An international team of astronomers, under the leadership of Earl Bellinger and Saskia Hekker of the Max Planck Institute for Solar System Research in Göttingen, has, for the first time, determined the deep inner structure of two stars based on their oscillations.

Our sun, and most other stars, experience pulsations that spread through the star's interior as sound waves. The frequencies of these waves are imprinted on the light of the star, and can be later seen by astronomers here on Earth. Similar to how seismologists decipher the of our planet by analyzing earthquakes, astronomers determine the properties of stars from their pulsations—a field called asteroseismology. Now, for the first time, a detailed analysis of these pulsations has enabled Earl Bellinger, Saskia Hekker and their colleagues to measure the internal structure of two distant stars.

The two stars they analyzed are part of the 16 Cygni system (known as 16 Cyg A and 16 Cyg B) and both are very similar to our own sun. "Due to their small distance of only 70 light years, these stars are relatively bright and thus ideally suited for our analysis," says lead author Earl Bellinger. "Previously, it was only possible to make models of the stars' interiors. Now we can measure them."

To make a of a star's interior, astrophysicists vary stellar evolution models until one of them fits to the observed frequency spectrum. However, the pulsations of the theoretical models often differ from those of the stars, most likely due to some stellar physics still being unknown.

Bellinger and Hekker therefore decided to use the inverse method. Here, they derived the local properties of the stellar interior from the observed frequencies. This method depends less on theoretical assumptions, but it requires excellent measurement data quality and is mathematically challenging.

Using the inverse method, the researchers looked more than 500,000 km deep into the stars—and found that the speed of sound in the central regions is greater than predicted by the models. "In the case of 16 Cyg B, these differences can be explained by correcting what we thought to be the mass and the size of the star," says Bellinger. In the case of 16 Cyg A, however, the cause of the discrepancies could not be identified.

It is possible that as-yet unknown physical phenomena are not sufficiently taken into account by the current evolutionary models. "Elements that were created in the early phases of the star's evolution may have been transported from the core of the star to its outer layers," explains Bellinger. "This would change the internal stratification of the star, which then affects how it oscillates."

This first structural analysis of the two stars will be followed by more. "Ten to 20 additional stars suitable for such an analysis can be found in the data from the Kepler Space Telescope," says Saskia Hekker, who leads the Stellar Ages and Galactic Evolution (SAGE) Research Group at the Max Planck Institute in Göttingen. In the future, NASA's TESS mission (Transiting Exoplanet Survey Satellite) and the PLATO (Planetary Transits and Oscillation of Stars) space telescope planned by the European Space Agency (ESA) will collect even more data for this research field.

The inverse method delivers new insights that will help to improve our understanding of the physics that happens in stars. This will lead to better stellar models, which will then improve our ability to predict the future evolution of the sun and other in our galaxy.

Explore further: Neutron stars on the brink of collapse

More information: Earl P. Bellinger et al. Model-independent Measurement of Internal Stellar Structure in 16 Cygni A and B, The Astrophysical Journal (2017). DOI: 10.3847/1538-4357/aa9848

Related Stories

Neutron stars on the brink of collapse

December 5, 2017

When a massive star dies, its core contracts. In a supernova explosion, the star's outer layers are expelled, leaving behind an ultra-compact neutron star. For the first time, the LIGO and Virgo Observatories have recently ...

Kepler satellite discovers variability in the Seven Sisters

August 25, 2017

The Seven Sisters, as they were known to the ancient Greeks, are now known to modern astronomers as the Pleiades star cluster – a set of stars which are visible to the naked eye and have been studied for thousands of years ...

Solar-like oscillations in other stars

December 12, 2016

Our sun vibrates due to pressure waves generated by turbulence in its upper layers (the layers dominated by convective gas motions). Helioseismology is the name given to the study of these oscillations, which can shed light ...

Distant star is roundest object ever observed in nature

November 16, 2016

Stars are not perfect spheres. While they rotate, they become flat due to the centrifugal force. A team of researchers around Laurent Gizon from the Max Planck Institute for Solar System Research and the University of Göttingen ...

X-rays reveal temperament of possible planet-hosting stars

September 6, 2017

A new study using data from NASA's Chandra X-ray Observatory and ESA's XMM-Newton suggests X-rays emitted by a planet's host star may provide critical clues to just how hospitable a star system could be. A team of researchers ...

Survivor of stellar collision is new type of pulsating star

June 28, 2013

A team of astronomers from the UK, Germany and Spain have observed the remnant of a stellar collision and discovered that its brightness varies in a way not seen before on this rare type of star. By analysing the patterns ...

Recommended for you

How massive can neutron stars be?

January 16, 2018

Astrophysicists at Goethe University Frankfurt set a new limit for the maximum mass of neutron stars: They cannot exceed 2.16 solar masses.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Jan 04, 2018
Finally. Now the authors of this method will determine the inner composition of Sun (Ø 1.392.000 km) and Jupiter (Equatorial radius 71,492 km). If they see the inner structure for very distant stars, this will be their cats cough (the only problem may be that the authors write nonsense).

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.