January 24, 2012
The Hunter Stuck in a Tree
Taurus the Bull is the sideways V near the center of the picture. Not really a constellation but an open cluster of stars, the Pleiades are the blue patch up and to the right of Taurus.
Clusters of stars like the Pleiades are groups of young, very hot and bright stars. They are around a hundred million years old, middle aged for their type.
Clusters like these form in dark nebulas, otherwise known as molecular clouds or stellar nurseries. The dark nebulae are regions of dense molecular hydrogen in interstellar space. Dense is a relative term. There are about 10 atoms per cubic centimeter in these clouds, as compared to about 30,000,000,000,000,000,000 atoms per cubic centimeter on earth.
Nevertheless, they have a huge volume, and they are dense enough to block out most of the stars behind them. We can see through them at longer wavelengths such as radio. Just by themselves these clouds are not particularly exciting. What happens when something compresses them is very exciting.
There are many ways these clouds can be compressed. A nearby star could go supernova, and the shock-waves could compress it, or it could run into another cloud, or several other variations of that theme. When the cloud is compressed, it becomes denser. The densest bits of the cloud start to form into a solid mass of molecules. This intensifies the gravity of the new ball of gas, and starts sucking more and more stuff into it.
Every time an atom hits it, it releases energy in the form of heat, and also contributes further to the gravitational pull. Eventually, these balls of gas start spinning, and form a disk. At this point they are proto-stars. These proto-stars suck the inside of the cloud into themselves, and eventually breach a hole in the side of the cloud, letting us see in. Some of these areas are just enormous with thousands of stars being born, while others are much smaller.
After a certain point, planets start forming out of the disk surrounding the proto-star, and once the material that makes up the star has squished in to a certain point, the temperature at the center reaches millions of degrees due to the intense pressure, and eventually hydrogen fusion starts to take place, producing helium.
It is at this point that it is considered a star. For your typical star, like our own, this process takes around 30 million years. That seems like a long time, but in astronomical scales it is not very long at all when you consider that a star can last for billions of years.
Back to this photo. I took it on the 12th of January, at around 9.30pm from Mt Tolmie. The exposure was 333 seconds or 5 and a half minutes.