I have a Windows/Linux dual-partition for my computer and every time I log-in to the Linux partition I am greeted by one of nine or so majestic astronomy pictures. The "Cosmos" desktop background is a slide show of various astronomical phenomena and it periodically changes from image to image while you work. I've had this background for a few years now, but I only recently wondered about the identities of the objects I was looking at. Some are easy to identify, such as Earth and Jupiter, but some were a mystery. I looked into the details of a few of the images. For some I could only find what type of object it was and not the name of the object, but the information that I found on the others I will share below. All the images are from http://hqwalls.blogspot.com/2010/07/cosmos-wallpapers-2560x1600.html. The majority of the information was gathered from http://www.spacetelescope.org/, http://www.universetoday.com/, and http://apod.nasa.gov/apod/.
Image 1: The Helix Nebula
The Helix Nebula is a planetary nebula approximately 700 light-years away, making it one of the closest planetary nebulae to Earth. The star at the center of the nebula is very old (and by "very old" I mean older than the sun and already past the red giant stage), and has already blown away its original outer-most gas and dust. Eventually, the star will become a white dwarf and the gas we can see now will have also been blown away. The structure of the Helix Nebula is interesting because there are "knots" in the shells of gas and dust. These knots are dense, intense patches of glowing gas. They have comet-like tails that point away from the star at the center of the nebula. Knots of nebulosity were first discovered in the Helix Nebula and have been found in other nebulae since then. The Helix Nebula got its name because the angle from which we view the nebula makes it look as if we are looking down the center of a helix.
Image 2: The Sombrero Galaxy
The Sombrero Galaxy is an unbarred spiral galaxy about 29 million light-years away from Earth. It has an unusually large central bulge and an extraordinarily well-defined dust lane. These characteristics, along with the fact that we view it edge on, make it look a bit like a sombrero. The ring contains mostly hydrogen gas and dust, and most of the stellar formation within the Sombrero Galaxy happens there. The Sombrero Galaxy also has one of the highest instances of globular clusters and one of the most massive black holes at its center. The black hole is estimated to have a mass of at least one billion solar masses. The galaxy cannot be seen with the naked eye, but it can be observed using only a 4-inch telescope.
Image 3: NGC 3370
NGC 3370 is also known as the Silverado Galaxy. It is a spiral galaxy about 98 million light-years away from Earth. It has well-defined spirals without a prominent central bulge. Both Cepheid stars, which vary in brightness in a predictable, periodic way, and type Ia supernovae have been found in this galaxy. Since Cepheids and type Ia supernovae have very distinctive light curves, they can be used to calculate the distance to the object they are found in. The age of the universe can then be estimated based on the distances to galaxies. This is possible because of the expansion of the universe. The farther away a galaxy is, the longer it has had to move away from our point of observation, and so the older it is. Once we know how distance and age correlate, we can convert distance to age, and the farthest galaxies can give us clues about how old the oldest objects in the universe are, thereby putting a lower bound on the age of the universe itself. Due to the presence of the Cepheid stars and type Ia supernovae, the distance to NGC 3370 could be measured quite accurately. So NGC 3370 would be a good galaxy to use in a study that was trying to find the relationship between distance and age, and in fact was used in such a study in 1994. You can also see many background galaxies in this image.
Image 4: The Whirlpool Galaxy
The Whirlpool Galaxy is a spiral galaxy about 23 million light-years away from Earth. We observe it almost directly face on, which gives us a magnificent view of its spiral structure. The smaller galaxy on the right side of the image is NGC 5195. The Whirlpool Galaxy is gravitationally interacting with NGC 5195, giving astronomers a chance to study galaxy interactions. The pink spots along the spiral arms are star-forming regions. The blue spots are star clusters. The other material in the arms is mostly dust and hydrogen gas. NGC 5195 is believed to help increase the number of star-forming regions. As NGC 5195 passes behind the Whirlpool Galaxy, NGC 5195's gravity ripples and compresses the gas in the spirals of the Whirlpool Galaxy. Once the gas is compressed enough, it starts to collapse under its own gravity and star-forming regions begin to form.
The only problem with knowing the identities and some of properties of the objects from the Linux Cosmos wallpaper is now every time somebody is near me and I'm working with Linux, he has to hear all about the image on my desktop. And 30 minutes later it changes to a new slide, and he has to listen to a new explanation all over again. On the other hand, I'm not so sure that a short, spontaneous astronomy lesson should be considered a problem. Either way, it's nice to be able see one of the images and no longer have to think "Oh, that's pretty, but what is it?" Now I know.
Great post! Sebastian (another 2nd year grad student) has a screen saver with those images and I always wondered what they were, but never thought to look them up. There's a lot of cool science going on in those images!
ReplyDeleteUsing faraway galaxies to figure out the age of the Universe is just d = v * t. We use supernovae and Cepheids to figure out d, the distance to the galaxy. The velocity v is the speed that the galaxy is moving away from us due to the expansion of the Universe. We can measure this speed using the Doppler shift - the light from an object that's moving away from us with velocity v is redshifted by a factor of (1 + v/c), so if we can measure the change in wavelength of an emission line such as a hydrogen Balmer line, then we know the velocity. We solve for the age of the Universe as t = d/v, where t is the time that it took to go from everything at the same point (the beginning of the Universe) to everything where it is now. Galaxies can be moving randomly relative to one another, in addition to the motion due to the expansion of the Universe, so we have to average together a bunch of faraway galaxies in order to average out the random motion.
Normally figuring out the age of the Universe is explained in terms of Hubble constants and general relativity and stuff, but to first order, we're just using d = v*t.
Terrific initiative here.
ReplyDeleteDan Seligson SSP Trustee, Class of '71