Quasars are intense sources of radio energy that appear as almost starlike points. For this reason, when they were first discovered in 1939 they came to be known as quasi-stellar radio sources, or quasars for short. Early on it was not entirely clear what these objects were. They were incredibly energetic, and they also tended to have very large redshifts, which implied that they were very far away. It was also noticed that quasars weren’t randomly scattered across the sky, but instead tended to clump together in groups.
A Shapley Galaxy
In the 1700s, William Herschel mapped the distribution of visible stars to determine the shape our galaxy. The result was a rather irregular distribution, and while Herschel had no way to determine the center of the Milky Way, he assumed the Sun was near the center. It was Shapley who, in 1918, demonstrated the Sun was not at the center of the Milky Way.
DRAGNs in the Sky
A radio galaxy is a galaxy that emits large amounts of radio waves. They were first discovered in the 1950s, but it wasn’t until the 1960s when a technique known as aperture synthesis was developed that we could resolve the distribution of radio emissions within a radio galaxy. It then became clear that many radio galaxies had a double-lobed structure emanating from a galactic core. It was suggested that these Double Radio Sources Associated with Galactic Nuclei be known a DRAGNs, though the term has never really caught on.
Immeasurable Heaven
Galaxies in the universe are not uniformly distributed, but are instead clumped together in groups known as clusters. These clusters are also clumped into larger superclusters, and superclusters are clumped into larger groups. If you image a bubble bath, and the way soapy-water bubble mix clumps to the intersection of the bubbles, the distribution of galaxies is somewhat similar.
Low Down on the Radio
Most radio telescopes have a traditional dish shape, such as Arecibo or Parkes. But there are other forms a radio telescope can take, for example the radio antenna on your car. You might not think of your car radio antenna as a telescope, but in a way it is.
CANDELS in the Dark
If you look at different galaxies in the universe, you begin to notice that they seem to fall into some broad types. Edwin Hubble was the first to categorize galaxies into different types, and he divided them into ellipticals, spirals and irregulars. He then further broke these categories into subgroups, and arranged them into what is now known as Hubble’s Tuning Fork diagram.
Line of Perseus
The Perseus cluster is a massive galactic cluster consisting of thousands of galaxies. It is often a focus of study because it is both massive and reasonably close (about 240 million light years away). Recently we’ve discovered some interesting x-rays coming from the region. The results have been published the Astrophysical Journal, showing there is an unexplained emission line in the x-ray spectrum.
Dying Embers
Determining the age of galaxies and globular clusters can be a bit of a challenge. There are several ways you can get a handle on galactic age. One of these is by looking at the ratio of red dwarf stars to larger stars. Red dwarf stars burn very slowly, so their lifetimes can be 100 billion years or more. Given that the universe is only about 14 billion years old, this means that red dwarfs haven’t had time to die off. Larger stars die off faster, so the higher the proportion of red dwarf stars, the older the galaxy should be.
Galaxy Wind
The Sun gives off a great deal of energy. As a result, ions from the upper atmosphere are pushed away from the Sun, producing what is known as the solar wind. With galaxies, a similar thing can occur. The center of many galaxies have the largest concentration of stars, and if that region is particularly active it can produce a “galactic wind” of molecules streaming away from the galactic center.