New observations have confirmed a 30-year-old theory that states the magnetic field produced by baby stars is key to their growth. In the new observation, reported in Nature, researchers observed how the gas and dust surrounding the star followed magnetic lines to fall onto the stellar surface.
These results were possible thanks to the GRAVITY instrument on the Very Large Telescope in Chile. The star in question is known as TW Hydrae, part of the T Tauri class of stars. It is about 80 percent of the mass of the Sun but less than 10 million years old.
“This star is special because it is very close to Earth at only 196 light-years away, and the disk of matter surrounding the star is directly facing us,” lead author Rebeca García López, from the Max Planck Institute for Astronomy, Dublin Institute for Advanced Studies, and University College Dublin, said in a statement. “This makes it an ideal candidate to probe how matter from a planet-forming disk is channeled on to the stellar surface.”
Stars form by the gravitational collapse inside nebulae, large clouds made mostly of hydrogen. The collapse creates the right condition for the core of the star to initiate nuclear fusion and make the newly formed celestial body spin. This rotation has important consequences that extend beyond the star to the nearby dust and gas. The rotation flattens the nebula into a disk and counter-intuitively makes it a lot more difficult for the material to reach the star. The orbiting material can’t be siphoned down to the star by gravity as it is moving too fast. For this to happen, it needs to slow down, which is the role the magnetic field plays (known as magnetospheric accretion).
GRAVITY was able to show that the magnetic field really does funnel gas and dust onto the star. The team hope to continue monitoring the star to understand if and how the magnetic field changes, as well as determine if it is a simple dynamo with a north and south pole, or something more complex.
“Magnetic fields can be much more complicated and have additional poles,” explained Thomas Henning, director at MPIA. “The fields can also change over time, which is part of a presumed explanation for the brightness variations of T Tauri stars.”
More observations are needed to have a complete understanding of how baby stars feed.