Thank you

Thank you for reading this blog this year. It has been an interesting experiment.

As we head into spring/summer term, and all the students head out of town, it'll get a litte quiet around here. AST 305 will be undergoing some revision over the summer as well, so we'll have to see what happens to this blog. Hopefully, we'll see you in September.

In the meantime, have a wonderful summer.

Clear skies!

Last call for your input...

If you've been reading this, please take just a minute to fill out this very short evaluation. Really, it's very short!

W13 evaluation request

We have come to the end of another semester, so it is time once again to ask your help!

Please take a moment to evaluate this blog. We really will be using the evaluation results, not only to determine if our student blogger did a good job, but also to determine if we want to continue this project in the future. So please, really, take a moment to give us your feedback by April 12. I promise to read every word of it.

Thanks for reading,
S.A.M.

Stars

A star is a sphere of plasma that is held together by gravity. Stars come in many different shapes and sizes. The size of a star is totally dependent upon the size of the molecular cloud it formed from.

Most stars that astronomers have discovered are on the main sequence because stars spend 90 percent of their lives on the main sequence. A star on the main sequence fuses hydrogen into helium. The lower the mass of the star, the longer it stays a main sequence star. For example, our Sun is 4.5 billion years old and it is still on the main sequence. It will remain on the main sequence for about another 4 billion years. If a star is much more massive than our Sun it could spend as little as a million years as a main sequence star. 

After a star moves off of the main sequence it becomes a red giant. It swells an enormous amount and it becomes much cooler than it was when it was on the main sequence. A star like our Sun will stay on the main sequence for about a million years. At the end of a stars life, depending on its mass, it will become a white dwarf, a neutron star, or a black hole. A star like our Sun will become a white dwarf.

Star Formation

Star Formation

Stars go through many stages while forming. The stages can take anywhere between hundreds of thousands of years to millions of years. The amount of time that it takes to form a star depends on the mass of the star forming. Very massive stars will take less time to form while stars that are smaller will take more time to form.

Stars begin their lives in molecular clouds. Molecular clouds are often referred to as a star's nursery because they are were stars begin their lives. Molecular clouds are very dense clouds that are dense enough to allow the formation of molecules. The most common molecule found in molecular clouds is Hydrogen. Hydrogen is the most abundant element in the Universe. It makes up about 75% of all ordinary matter found in the universe.

Molecular clouds are so dense that turbulence and fluctuations within them cause certain amounts of matter to join together. After this matter joins together, the dust and gas in this portion of the cloud begins to collapse under its own gravity. While it collapses the matter near its center get hotter and hotter. This core is known as a protostar. A protostar is the stage before a star begins nuclear fusion. This matter is known as a star only when it begins nuclear fusion.

 Here is an image of a molecular cloud:

 

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:

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.

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:

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.

Supernova

 

Black holes, their disks and how they behave in dwarf galaxies

Black holes generate energy and radiation (light) from the matter that falls onto them.  They accrete matter from orbiting celestial objects such as stars, planets, asteroids, comets, and other forms of debris. This accreted matter falls onto the black holes through their accretion disks and these disks produce the energy and radiation (light). This is the reason why we can "see" black holes, because we don't actually see the black hole we see the accretion disk. If there was not matter accretion  producing radiation (light) there would not be any light emitted from a black hole, hints the "black" hole. Here is a black hole; as you can see the very center is dark and the outer parts a luminous.

A black hole in a dwarf galaxy effects its surroundings differently than a black hole in a regular galaxy.  A black hole in a dwarf galaxy changes the speed of the objects a lot. It effects many more objects in a dwarf galaxy than a regular galaxy because a regular galaxy is much bigger and more spaced out than a dwarf galaxy.  Here is a picture of our Milky Way; the picture shows a band of stars left over by a dwarf galaxy collision with our Milky Way (seen in the blue). This leads astronomers to believe the Milky Way formed from a number of dwarf galaxies, that in previous years collided with one another.