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.