(presentation for Powell Observatory Open House, November 18, 2006)
When we think of the stars, we often think of pinpoints of light against the black backdrop of the night sky. We think of their fixed positions and constant shining. They are always there, unchanging from generation to generation. But we know in fact that stars do undergo changes, ranging from dramatic explosions to long term gradual change.
One key component to the story of a star's life is the concept of a stellar wind. Our own Sun blows a wind that sweeps past the Earth at about 400 kilometers per second (that is nearly 150,000 kph!). In fact, satellites launched from over 30 years ago have now traveled out into space, more than twice the distance of Pluto, and apper to have reached the boundary where the solar wind meets the gases that lie between the stars.
Mass loss from stars is common and normal, but the kind of mass loss that a star experiences depends on its type. The figure below summarizes the different winds and explosive effects that are found among stars.
Stellar winds leave their fingerprints all over our galaxy. Here are just a small sampling of the kind of effects that winds can have.
Dramatic examples of how stars like the Sun will terminate. These colorful and graceful appearing nebulae are the result of vigorous winds that blow off the outer stellar atmospheres during the red giant phase of Sun-like stars.
The left inset is a Hubble Space Telescope image of the massive star eta Carinae, perhaps the most massive star in our Galaxy (now thought to be a binary system). The bipolar bubble morphology is the result of an outburst in the late 1800's. At right is a false color image in X-rays from the Chandra satellite.
Sometimes two stars with strong winds can be found orbiting each. At left is a model for the colliding winds of the massive binary WR140. At right are observations of similar systems that form dust in the wind collision, creating a spiral emission pattern.
Sometimes stars explode as supernovae, expelling dozens of solar masses of gas back into space. A supernova is not an example of a regular ongoing wind, but rapid and violent ejection of gas from the star. Supernovae are extremely bright and can be seen essentially across the universe. Their power is also considerable in terms of stirring and heating up gas in the space between stars, even creates "fountains" of gas shooting up out of galaxies.
Here is an example of SN1987A that was a star that went supernova in the nearby Large Magellanic Cloud (before-after picture at left) and its mysterious triple rings that it illuminated from a previous wind phase (right).
Here Kepler's supernova remnant as seen in different kinds of light.
And here is a radio image of the neighborhood in the center of the Milky Way, revealing several gaseous bubbles identified as remains of past supernova explosions.