A multinational team of astrophysicists has recorded the ‘sounds’ from some of the oldest stars in our Milky Way Galaxy.
This wide-field view is centered on the globular star cluster Messier 4 (also known as NGC 6121) in the constellation of Scorpius. It is a color composite made from exposures from the Digitized Sky Survey 2 (DSS2). Image credit: ESO / Digitized Sky Survey 2 / Davide De Martin.
The team, led by Dr. Andrea Miglio from the University of Birmingham, has detected the resonant acoustic oscillations of eight ancient stars in the spectacular globular cluster Messier 4.
“Seven of the stars are on the red-giant branch; the eighth is on the red horizontal branch,” the scientists said.
Messier 4 is one of the oldest known star clusters in the Galaxy, some 13 billion years old.
This ball of tens of thousands of stars is also one of the nearest globular clusters in the sky at an estimated distance of about 7,200 light-years.
Using data from the NASA Kepler/K2 mission, Dr. Miglio and co-authors have studied the resonant oscillations of the Messier 4 stars using a technique called asteroseismology.
“The oscillations are beyond the normal human hearing range, but here they have been transformed into something audible,” the scientists said.
These oscillations lead to miniscule changes or pulses in brightness, and are caused by sound trapped inside the stars. By measuring the tones in this ‘stellar music’, it is possible to determine the mass and age of individual stars.
This discovery opens the door to using asteroseismology to study the very early history of our Galaxy.
“The K2 satellite observations are in close agreement with previous theoretical calculations of the properties of this type of stars, making the astronomers confident that their star models are close to being correct – that scales, yardsticks and other tools for measuring the stars have the right calibrations, so to speak,” the astronomers said.
“We were thrilled to be able to listen to some of the stellar relics of the early Universe,” said Dr. Miglio, first author on a paper published in the Monthly Notices of the Royal Astronomical Society this week.
“The stars we have studied really are living fossils from the time of the formation of our Galaxy, and we now hope be able to unlock the secrets of how spiral galaxies, like our own, formed and evolved.”
“The age scale of stars has so far been restricted to relatively young stars, limiting our ability to probe the early history of our Galaxy. In this research we have been able to prove that asteroseismology can give precise and accurate ages for the oldest stars in the Galaxy,” added co-author Dr. Guy Davies, from the University of Birmingham.
“Just as archaeologists can reveal the past by excavating the earth, so we can use sound inside the stars to perform Galactic archaeology,” said co-author Prof. Bill Chaplin, also from the University of Birmingham.
“We are very happy to see our collective efforts succeed,” said co-author Dr. Karsten Brogaard of Aarhus University.
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A. Miglio et al. Detection of solar-like oscillations in relics of the Milky Way: asteroseismology of K giants in M4 using data from the NASA K2 mission. MNRAS, published online June 6, 2016; doi: 10.1093/mnrasl/slw102
