Strange Stars Lead to Reconsidering Galactic Evolution

If there’s one difference I notice between Science and Religion, it’s that when questions come up and something unexpected flies in the face of a well-established principle, Science gets excited, Religion gets defensive.  I’m always on the lookout for new data that causes us to rethink the ideas we have, and when I find something, I get excited because it means we’ve found something that has been elusive for a long time.  Isaac Asimov said it best:

The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ but ‘That’s funny…’

– Isaac Asimov

Astronomers have recently been using a new method to determine the age and composition of stars that has been dubbed ‘asteroseismology.’  It uses the idea that stars oscillate at different frequencies, and different frequencies penetrate to different depths within the star, revealing information about the star’s inner structure.  The oscillatory modes can be observed as subtle brightness and size changes of the star itself.  Once we know the internal structure of a star, we can find a very accurate determination of its age.  You can find a more detailed explanation here.  The field is growing within astronomy as new methods are developed to precisely study the variations due to stellar vibrations.

Different vibration modes penetrate to different depths within a star. Credit: Toskala CC 3.0

An international team of astronomers led by Cristina Chiappini from the Leibniz Institute for Astrophysics Potsdam has discovered a group of stars that are much younger than they should be.   By using asteroseismology they found that the age of the stars was very different from what was inferred by looking at spectroscopic data.

Historically, astronomers have indicated the ages of stars by looking at their chemical composition, determining this through spectroscopy.  Spectroscopy involves looking at the light from stars broken into the colours of the visible spectrum.  Different elements absorb different wavelengths of light, so when the starlight reaches Earth, we can look at what wavelengths are missing and correlate them to elements that make up the star.  In terms of chemical composition, older stars have lower ‘metallicity,’ which is the term used to measure abundance of elements heavier than Hydrogen and Helium, meaning the ‘metals’ to an astronomer represent everything else (Oxygen, Nitrogen, Carbon, etc).  Younger stars were able to form with some of these heavier elements already present, since ancient stars produced these elements and then died off, enriching the interstellar medium.

Location of the red giants studied by CoRoGEE in the Milky Way. The red stars show the ones for which the chemical clock does not work. Credit: F. Anders

This age difference has only been seen in a small population of stars in the dataset, which is a likely reason for why they hadn’t been noticed previously.  The fact that these stars exist means that our understanding of the chemical enrichment of the Milky Way is flawed and needs to be altered to explain the existence of these stars.

I am excited to see what happens in the future.  What new explanation will fit the data we see and how much will our previous theory change to account for these new observations? I can’t wait to see the results.  It’s the essence of the scientific method!

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