Size doesn’t matter when it comes to magnetism in stars. Astronomers have discovered an ultra-cool red dwarf star with an average magnetic field comparable to the strongest field produced by the Sun during peak activity.
Using the powerful radio telescope ALMA (Atacama Large Millimeter Array), the team was able to observe the emission generated by electrons being pushed around by the strong magnetic field. As electrons released by the star move quickly around field lines, they emit synchrotron radiation that ALMA can detect. ALMA detected this in a single four-hour observation, which implies the emission is continuous.
The star, called TVLM 513-46546, is located just 35 light-years from Earth. It's a fast-rotating object, spinning in just two hours, with nine percent of the mass of the Sun and an average surface temperature of 2,500 Kelvins (2,200°C, 4,000°F). In terms of size and temperature, the red dwarf sits in the middle between stars (which fuse hydrogen) and brown dwarfs (which don’t).
The lack of nuclear fusion makes the presence of the strong magnetic field even more mysterious. Magnetism in the Sun comes from the movement of charged particles in its interior, similar to an electromagnet where electric currents generate a magnetic field. As it stands, it is unclear as to where its magnetic field originates.
"This star is a very different beast from our Sun, magnetically speaking," said co-author Edo Berger in a statement.
Red dwarfs are the most common stars in the Milky Way, and this study, alongside other recent news, spells disaster for planets around them. The continuous flare emissions from TVLM 513-46546 are 10,000 brighter than what our own Sun regularly produces.
"If we lived around a star like this one, we wouldn’t have any satellite communications. In fact, it might be extremely difficult for life to evolve at all in such a stormy environment," said lead author Peter Williams.
The discovery has important implications in the search for life in our galaxy. We don’t know if this is an exceptional red dwarf or a normal one. Future observations will have to characterize how common these flaring stars are and under what conditions, if any, life could evolve around these objects.
The paper is published in The Astrophysical Journal.
2
