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\begin{document}

\title{Stellar Ultrasound}


\author[ ]{Matteo Cantiello}

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\textbf{Stellar ultrasounds}.~Certain stars pulsate and can effectively
be considered huge musical instruments: depending on their size and
internal structure, they can oscillate at different frequencies,
somewhat similar to spherical drums of different size, shape and
material. The waves that propagate through the star can bring to surface
precious information about the internal regions they crossed. This is
similar to what seismologists do with the planet: they study at the
surface waves excited by earthquakes to retrieve information about the
structure and properties of the Earth's inner regions they crossed. The
waves crossing a star can be of different types, some are similar to
sound waves, others to surf waves. Different waves probe different
regions of the stellar plasma, so depending on which type of waves
astronomers `listen to', they can retrieve properties relative to
different stellar depth. This is the basic idea behind the `stellar
ultrasound'.~

It turns out that the oscillations induced by these different types of
waves can be encoded directly in the light of the star. This is awesome,
because the sound can not travel in the vacuum that is the medium
between stars, but light can. Also it travels much faster. This opens up
a new branch of astronomy called ``Asteroseismology'', something only
recently we started applying to large collections of stars because it
requires observations from space. We can now determine the internal
properties of thousands of stars. Some of these stars are thousands of
light years away! And we found many surprises. The latest discovery is
the potential ubiquity of ultra-strong magnetic fields hiding in the
stellar cores. The stellar core is the region where thermonuclear
reactions are at play, making the star shine and basically creating all
the elements of which humans are made off as a byproduct (except
Hydrogen). These magnetic fields are million of times stronger than the
Earth's magnetic field, and can change completely the way a star lives
and dies! For example, they might be playing a role in producing the
brightest explosions in the cosmos\ldots{} ~

\par\null\par\null

Stars are huge musical instruments, playing music with their starlight.
This twinkling carries the secret story of their magnetic cores

\par\null

Source:

- Science
(\url{http://science.sciencemag.org/content/350/6259/423.abstract}),

- Nature
(\url{http://www.nature.com/nature/journal/v529/n7586/full/nature16171.html})

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