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