The Interstellar Medium along the Sun’s Trajectory
Published on Jan 11, 2007 at 12:55 pm.
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Filed under conference blogging, interstellar medium.
With things finally winding down, I get to post a bit more about some of the things that I saw at the AAS Meeting. I had been looking to do some of this quite some time ago, but this has been a pretty wild week.
Earlier in the week, I met a young man, Ryland Brooks, from Colby College, who was presenting a poster about the interstellar medium. It was an interesting poster. Now, one of the things that impressed me was that he is an undergraduate student! He was a participant in a program at UT Austin that allowed undergraduate students to do some actual science unter the supervision of a researcher. Quite impressive!
His poster was about mapping the interstellar medium along the Sun’s path. Let me explain. First of all, the Sun doesn’t just sit still in space. It orbits the center of our galaxy. Interstellar space isn’t empty, either. Rather, the space between the stars in our galaxy is filled with a very tenuous gas and dust. We call this the interstellar medium. This interstellar medium is also orbiting in the galaxy, but not exactly the same as the Sun. So, the Sun is slowly passing through the interstellar medium. But, the interstellar medium isn’t uniform. In places it is thicker. If it is thick enough and cool enough, its own gravity can cause it to collapse to form new stars. In other places, the IM is thinner. In fact, the IM is filled with bubbles of low density material. Most of these bubbles are not just thinner, but warmer (more energetic gasses) than the surrounding IM. It is believed that very hot luminous stars can blow bubbles in the IM, but the larger ones are produced by supernovae explosions. In fact, our Sun is currently inside such a bubble, called the Local Bubble (real original name, right?). The Sun is off center and moving with respect to the Local Bubble. So, what this poster was presenting was a map of the density fluctuations along the path that the Sun is taking.
He finds that the Sun will be passing through or near several somewhat thicker regions over the next 28 million years until it reaches the edge of the Local Bubble. Then, it will encounter much thicker material.
So what? Well, there is reason to be interested. In earlier posts, I had mentioned cosmic rays. Some of the intermediate cosmic rays come from near the heliopause (where the Sun’s influence loses way to the interstellar medium). For many years, astronomers thougth that the heliopause was much closer than it is. Many thought that it would be dozens of astronomical units from the Sun. Instead, it is about 100 AU from the Sun. Why is it so far away? Well, the interstellar medium turns out to be thinner in the vicinity of the Sun than was expected. That will change when we pass through thicker regions of the IM. When that happens, the heliopause will likely be closer. And, that could influence cosmic ray intensities on Earth.
I have read other papers that suggest a climate change might be associated with passing through unusually thin or thick regions of the IM. If so, then in about 30 million years, Earth may be in for a big climate change. And mapping the IM along the Sun’s trajectory is one way of looking forward. And, this was done by a student. Pretty cool.
-Astroprof
