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.

My experience

Thanks to this student blog, over the semester, I have deepened my knowledge of some very useful astronomy concepts.  I have learned more about binary systems, black holes, star formation, exoplanets, and many other extremely interesting astronomy concepts. 

Astronomy is my major and it is a very important part of my life so doing something i love and getting to express some of my thoughts about it to this big internet community has been a blessing.  I loved the fact that I got so many views and I even got comments and or questions on some of my blog posts.  I have to say that I liked the questions the most because they were really good questions. 

I want to thank everyone for ready this blog and I hope you all will continue to read the blog in the future!

ASTRONOMY IS THE FUTURE!!!!!!!!

Colloquium November 29

On November 29, 2012 the University of Michigan welcomed Andy Fabian to speak on Black holes and their environments.

 

Andy Fabian is a professor at the University of Cambridge. He has received many awards through out his career and he has taught around the world.

During his lecture Fabian focused primarily on the way we view black holes. He talked about how the amount of radiation (energy from matter around the black hole) depends on what surrounds the black hole.  He gave details about how we view the spectra of the released energy. He said that the radiation that is sent out by black holes is often in the X-ray band because it has such high energy. 

Fabian talked about how the energy of a black hole varies if it has a spinning accretion disk or a non spinning accretion disk.  He said that spinning accretion disks release 5 times more energy (radiation) than non spinning disks release.  He also said that some black hole shoot jets and these jets can go out as far as 5 Mpcs.

Black hole's affected by surrounding matter

Many black holes are affected by matter that is found around them. These objects that affect black       holes include orbiting stars, gas, planetary objects, comets, asteroids,  and many other celestial object.

When Black holes are affected astronomers can view the effects through X-ray emissions from the luminous black holes.  Astronomers, through X-ray emissions, can see the black hole's strong gravitational affects, its gravity redshifts, its gravitational light bending, its delays, and its dragging of inertial frames in the Kerr metric. 

The accretion disks that surround black holes include lots of dust that affect the energy outputs of the black holes.  These disks can create soft X-ray emission or hard X-ray emission.  These accretion disks can surround both spinning and non spinning black holes.  However, spinning black holes produce 5 times as much power as non spinning black holes.

End of Term Evaluation

If you've been reading this blog this term, we'd really appreciate it if you could take a minute or two to let us know what you thought.
It really is quick!

Colluqium November 15

On November 15, 2012 the University of Michigan welcomed Dennis Bodewits to speak on comets and asteroids.

Dennis Bodewits is an assistant research scientist in the Astronomy Department at the University of Maryland.  "His research emphasizes comets and asteroids, and he is a member of the EPOXI/Deep Impact and Stardust-Next science teams. His observational studies encompass X-ray, UV and visible regions, and makes use of mostly space-born telescopes, such as Swift, Chandra, and XMM-Newton".(http://www.astro.umd.edu/people/dennis.html)

In his speech Bodewits focused on the roles comets and asteroids played in the creation of water on Earth.  He had videos and many photos of artistic interpretations of water formation of Earth. Bodewits also gave detailed explanations of the compositions of asteroids and comets.

For more information on comets here is a link: http://www.michastrostudent.blogspot.com/2012/11/comets.html. For more information on asteroids here is a link: http://www.michastrostudent.blogspot.com/2012/11/asteroids.html. For more information on water formation on Earth here is a link: http://www.michastrostudent.blogspot.com/2012/11/the-water-of-earth-contribution-of.html.

The Water of Earth. The Contribution of Asteroids, Comets, and Meteors

Earth is a fascinating and amazing planet to study because it has surface water. Surface water is an extremely valuable resource. It is arguably the most valuable resource on Earth because it is essential to all living organisms and it formed over a large amount of time. Water formed on Earth through a process that lasted millions of years. 

The process that allowed water to form on Earth included; asteroids, comets, and meteors. Astronomers have many theories about this process. Some astronomers have different beliefs about the ratio of comets, meteors, and asteroids that were involved in the formation of water on Earth. All of the different theories that involve the different ratios and time scales can all be justified because no one really knows how water formed on the surface of the Earth. It is impossible to know because humans had not even been created when water formed on Earth. However, astronomers know that asteroids, meteors, and comets played a role in water formation on the surface of earth because the water had to have come from some outside source. 

Asteroids, comets, and meteors are very important celestial bodies that have been found in our solar system. Most importantly asteroids, comets, and meteors, contributed to water formation on the surface of the Earth. These celestial bodies, any natural body outside of the solar system, have been studied for many years and they are all very different from one another. Their differences make them very interesting. 

Asteroids are airless objects, most commonly found in the asteroid belt. The asteroid belt is located Mars and Jupiter. For more information on asteroids here is a link http://www.michastrostudent.blogspot.com/2012/11/asteroids.html

Comets are icy objects, most commonly found in the Oort cloud. The Oort cloud is a spherical cloud located 50,000 AU from the Sun. For more information on comets here is a link http://www.michastrostudent.blogspot.com/2012/11/comets.html

Meteors are dust to bolder sized particles of debris that are found in the solar system. 

Meteorites that astronomers have studied on Earth have hydrogen isotope ratios that help explain how elements like hydrogen and nitrogen got on the Earth. 

The biggest question astronomers are trying to answer is how volatiles like hydrogen, nitrogen, and carbon first arrived on Earth. Astronomers mostly believe that these elements arrived on Earth through collisions with comets and asteroids. One of the most accepted theories on how water formed on Earth suggests that during the creation of the solar system Jupiter and Saturn's orbits were disturbed and that caused comets in the outer solar system to move inward and later make their way towards Earth. These comets collided with Earth and left ice and other elements behind. Later when an asteroid collided with the Earth, the ice was melted and liquid water was then formed on the surface of the Earth. This process, according to astronomers, happened many times and it took millions of years.

Comets

Comets are known as “dirty snowballs,” because they consist of a mixture of ices (both of water and frozen gases), carbon dioxide, ammonia, methane, and dust. The core of a comet is solid and it consists of ice and dust.

Comets also have two tails. The first tail is an ion tail. The ion tail is blue because it consists of ionized CO+ and it scatters blue light. The second tail is the dust tail. The dust tail is green and consists of the dust that is pushed off of the comet and reflects radiation from other sources. The tails of a comet can reach 160 million kilometer long. 

 

The average comet has a mass of 10^14 kg, a diameter of 20 km, a density of 0.6 g/cm^3, and an albedo of .05.

Comets are mostly located in the Oort cloud, except for the occasional comets that streaks through the inner solar system. The Oort cloud holds millions and millions of comets and the Oort cloud is found much farther out than the orbit of Pluto. It is generally believed that we got our water when comets collided with the Earth.

Asteroids

Asteroids are marvelous celestial objects, not only because they played a huge role in water formation on Earth through various collisions with Earth's surface, but because they are so complex. Asteroids are irregularly shaped, rocky objects that usually are considered small objects or minor planets. They are rocky fragments that were left over from 4.6 billion years ago when the solar system formed. 

 The average asteroid is very complex because it has a diameter of 20 km, a density of 0.3 g/cm^3, and an albedo of less than .05. They also have an average surface temperature of 100 degrees Fahrenheit. 

 Asteroids are also very interesting because they fall into three different categories based on their compositions; C-type (carbonaceous) asteroids, S-type (sillicaceous) asteroids, and M-type (metallic) asteroids. C-type asteroids are greyish and are the most common asteroids. They make up 75 percent of all known asteroids in the solar system. S-type asteroids are reddish and greenish in color and they make up 17 percent of all known asteroids. M-type asteroids are red in color, consist of mostly nickle, and are located mostly in the middle of the asteroid belt. 

 Asteroids orbit the Sun in elliptical orbits in the asteroid belt that is located between Mars and Jupiter. The asteroid belt is made up of many different sized asteroids. The asteroid belt holds more than a million asteroids, of which 200 are larger than 60 km in diameter and 750,000 are larger than 1 kilometer in diameter. Half of the mass that is found in the asteroid belt comes from the four largest asteroids. The four largest asteroids are Ceres, Vesta, Pallas, and Hygiea. 

 The total mass of all the asteroids in the solar system is less than the mass of the Moon, but asteroids are still very dangerous. Many asteroids collided with the Earth in the past. The asteroids that collided with the Earth, depending on their sizes, caused great amounts of damage. Therefore many astronomers study the orbital paths of asteroids and believe that these earlier collisions, together with earlier comet collisions, contributed to water formation on Earth's surface.