Tuesday, February 19, 2013

Green Pea Galaxy

A Green Pea galaxy is a galaxy that is undergoing high rates of star formation. Astronomers believe that they might be a type of Blue Compact Galaxy. They are named Green Pea galaxies because they appear very small in size and they look greenish.

These galaxies where discovered in 2007, by a couple of volunteer astronomers. They were discovered at redshifts between 0.112 and 0.360. The galaxies are very compact and emit a lot of lines from oxygen. The biggest these galaxies get is around 16,000 light years or 5,000 pc. So the Milky Way is about 6.25 times as big as a Green Pea galaxy. Here is an image of a Green Pea galaxy:

Monday, February 18, 2013

The Magellan telescopes

The Magellan telescopes are large custom built telescopes. They were built by the Carnegie Institution of Washington. They are located in Chile. The telescopes were built on the behave of the University of Michigan, the University of Arizona, the University of Harvard, and the Massachusetts Institute of Technology. Many people use these telescopes, including professors, Ph.D. Students, and postdoctoral astronomers. Each University shares the time equal on the telescopes.

The Magellan telescopes are very large. The main mirrors are f/1.25 paraboloids. Each of the mirrors are made of borosilicate glass and they weigh 21,000 pounds each. It took a really long time to build each mirror. It took 6 months to build the mold that the glass mirrors were made in. It then took 2 days to put the glass into the molds. After the glass was placed into the molds, it took 3 months for the glass to cool. Lastly, each of the mirrors had to be polished for several months. It also took a lot of time for the telescopes mount and track to be built. 

The Magellan telescopes staring operating in the early 2000s.

Thursday, February 14, 2013

Discovery of Exoplanet systems part 2

The second indirect method of exoplanet detection is the transit method.  The transit method can determine an  exoplanet's radius. Astronomers use this method to determine the presence of an exoplanet by visualizing a stars decrease in brightness. If an exoplanet is present, when it passes in front of its companion star, there is a detectable drop in the star's apparent brightness. The amount that the star's brightness drops depends completely on the size of the exoplanet.  Here are some images and a video:


Direct detection of exoplanets is completed through direct imaging.  Planets are very faint in brightness when compared to stars. They produce little radiation.  A planets radiation can be easily lost due to the brightness of its parent star.  Consequently, it is extremely difficult to detect planets using this method when a planet is small.  This method is usually used to detect planets much larger than Jupiter. Here is an image:

Wednesday, February 13, 2013

Discovery of Exoplanet systems part 1

There are several methods used to detect exoplanet systems. These methods are both indirect and direct. When referring to a direct method, this means that we can view the exoplanet directly. On the other hand, while referring to an indirect method, this means we cannot observe the exoplanet directly.  It means we infer that the planet is there based on shadows, the speeds of objects around it, and the apparent brightness of the companion star. The indirect methods of exoplanet detection include; the radial velocity method,  and the transit method.  The direct method used to detect exoplanets is direct imaging.

The radial velocity method uses a star's orbital response to a planet with respect to the Earth.  A star that has a planet will move a little bit in its orbit as a response to the planet's gravity.  The orbital change leads to a variation in speed of the star with respect to the Earth.  The speed the star moves toward or away from the Earth would change. The star's spectral lines will be displaced when looking from Earth due to the Doppler effect (http://michastrostudent.blogspot.com/2013/02/doppler-effect.html).  These variations are used to confirm the presence of an exoplanet.

to be continued....

Doppler Effect

The Doppler effect is also known as the Doppler shift.  It refers to a change in a wave's frequency with respect to an observer.  It was named after Christian Doppler.  Christian Doppler was an Austrian physicist and he proposed the theory of Doppler shift in 1842.  Here is an image of C. Doppler:

Many experiments have been performed to confirm the Doppler effect.  Buys-Ballot conducted one of the most famous experiments.  He used sound waves in his experiment.  He used a group of musicians and a train.  As the train passed him he asked the musicians to play a constant note.  The variation in the sound of the note helped him detect the Doppler shift.  Here is an image of Buys-Ballot:

How is this 'Doppler effect' important to Astronomy?  It helps astronomers study electromagnetic waves in all portions of the spectrum.  Since we know that there is an inverse relationship between wavelength and frequency, we can use Doppler shift in terms of wavelength.  We know, from the Doppler shift, that an object moving toward us will have a decreased wavelength and appear blueshifted, and an object moving away from us will have a increased wavelength and appear redshifted.  Doppler shift is also important when using the radial velocity method to detect exoplanets.

Friday, February 1, 2013