Tiny star has giant flares
Have you ever heard about solar flares? A solar flare is a giant explosion on the surface of the Sun. It blows dangerous particles into space. When some of those charged particles arrive at Earth, they produce beautiful auroras (also known as the northern or southern lights). But the particles can also disturb radio communications and satellite electronics, or damage electrical power plants.
You would expect that a tiny dwarf star has fewer and less energetic flares than a star like our own Sun. But ALMA has discovered extremely powerful flares from a red dwarf star that is ten times less massive than the Sun.
It was already known that the red dwarf star (known as TVLM 513-46546) has a very strong magnetic field – a few hundred times stronger than the magnetic field of the Sun. No one knows exactly how this strong field is generated. It might be related to the fast rotation of the red dwarf: it turns around its axis once every two hours. For comparison: the rotation period of the Sun is about 25 days.
During a 4-hour observation of TVLM 513-46546, ALMA detected powerful radio waves from the red dwarf star, at a wavelength of about 3 millimetres. These radio waves are produced when energetic particles are whirled around by strong magnetic fields.
The radio waves of the red dwarf are 10,000 times more energetic than similar radio waves from the Sun. That means there must be more charged particles, moving at much higher velocities. The only possible origin of these particles is continuous giant flare activity on the surface of the star.
Many red dwarf stars are accompanied by planets. No one knows if TVLM 513-46546 also has a planetary system. But if it has, life on these planets will be impossible because of the lethal radiation.
In the future, ALMA will study more red dwarf stars in search of tell-tale radio waves from stellar flares. Thus, astronomers hope to find out if this particular star is an exception.
TVLM 513-46546 is a small and cool star at a distance of 35 light-years in the constellation Boötes. Because of its low surface temperature, it mainly emits red light, and since it is small and light-weight, it is labelled as a red dwarf star. Red dwarf stars are very common in the Milky Way – there may be two hundred billion of them. They are about as large as Jupiter, but much more massive – TVLM 513-46546 has ten percent of the mass of the Sun.
TVLM 513-46546 was studied in April 2015 by Peter Williams and Edo Berger of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, in the USA. Peter and Edo worked together with four other astronomers from the United Kingdom. The team published their results in an article in the professional magazine Astrophysical Journal.