Stellar Wind

The sun and similar stars form from collapsing clouds of gas and dust. After the star forms, the leftover material still surrounds it in a cocoon of gas and dust. How do stars like the sun shed their cocoons? One way is stellar winds. Astronomers think that shortly after the sun formed it went through a period when it had a very strong solar wind, which helped blow away the cocoon. It is difficult to know how accurate this scenario is because no one was around to witness the birth of the solar system.

We can however watch the birth of other stars similar to the sun. T Tauri stars are stars in the process of forming that astronomers think will eventually have properties similar to the sun's. Among other properties T Tauri stars show evidence of strong stellar winds. They also show a range of thick and thin circumstellar cocoons. Studying the stellar winds from T Tauri stars will help us understand how the Sun and similar stars shed their initial cocoons.

Many young stars show bipolar outflows, which are two streams of material blowing away from the star in opposite directions. They usually occur in the birth of stars more massive than the sun. The bipolar outflow stage only lasts about 10,000 years or so, but during that time we see a strong stellar wind from the newly forming star. Why is the outflow bipolar? One theory suggests that the outflow is bipolar because an equatorial disk of material surrounding the star constrains the wind to flow out from the two polar regions. This disk may be the material that will eventually form planets around the star. Another possibility is that the star's magnetic field forces the outflow into a direction perpendicular to the equatorial disk. The study of stellar winds from newly forming stars will eventually provide us with clues to help us understand how the sun and solar system formed.