Physics 162H Honors Project: Galaxies
Galaxies are collections of billions of stars and interstellar matter all accreting around a central point. The large-scale structure of a galaxy involves a central nucleus, which may house a super-massive black hole in some cases. The nucleus consists of densely packed stars, with lighter concentrations trailing out to the edges. There are several types of galaxies, as the drawing below shows. There are two basic types: the Spiral and the Elliptical.
Spiral galaxies have a readily identifiable shape. The nucleus of the galaxy appears as a bright glowing bulge, with two or more arms spiraling out from the middle bulge in concentric loops. These galaxies are slowly spinning, and their shape may be a result of this. The squeezing of the interstellar gas and dust by coiled waves of gas compression, sometimes refered to as Spiral Density Waves, forms new stars in rings. We see the outlines of the dense clouds of gas and new stars formed by these waves. There are lesser evolved versions of spiral galaxies, known as barred spirals, which have a readily identifiable expanse of open space contained in them, bridged by a 'bar' of matter across the center connected to the trailing arms. Barred Spirals have their own classification similar to standard spiral galaxies.
Elliptical galaxies are more rounded concentrations of stars, resembling a galactic bulge without spiral arms. Sometimes they are spirals that are so edge on that the arms are nearly invisible. Some ellipticals are dwarf galaxies, and others are older cores whose arms may have already been consumed by the center or have been stripped off in a collision with another more massive galaxy.
For this project, you will be required to observe a galaxy. Chances of a good photo are small, so sketching and visual observations are the best. More than likely, all the galaxies the observatory manager will be able to reliably locate for you will be spirals which are very close. The best ones viewed through the Davis Hall Observatory are listed below.
- Devise a Plan of Attack. Consult with the manager and choose the objects you wish to try to view through the telescope. Messier objects are the most likely to be found, so it is strongly recommended that you stick to the Messier Catalog. It is also recommended that you choose objects visible in the northern hemisphere. Find coordinates for your desired objects.
For this project, there are several recommended objects:
- M-31, The Great Andromeda Galaxy.
- M-51, The Whirlpool Galaxy.
- M-81 + 82, in Ursa Major.
- Small concentrations are visible in Leo, Corona Borealis and Virgo, if you are so inclined.
- Locate each object in the telescope at Davis Hall.
- With the manager's assistance, attach either a camera or the CCD to the scope. An option for a very faint galaxy is to observe it visually and attempt to sketch a picture. Include background stars in the picture for reference.
- Capture at least one image, or more if you choose. Try several different images in different scopes and powers of magnification.
- With use of photography, or with the CCD images, the pictures may be enlarged so that they may be more visible. If you can capture an image of the spiral arms, that would be fantastic. The bulge is sufficient for this project.
Unless you want to overlap slightly on the theme of the cosmology project, there will be very little interpretation. It is enough to collect images and comment on them. Include talk of spiral structure, the density and proximity of galactic concentrations, and the various types of galaxies, from the Meganellic Clouds to the Great Andromeda spiral. The Andromeda galaxy is an excellent spiral which is easy to locate.