Astronomy/Active Galaxies

Astronomy for the 2011 season is centered around quasars, AGNs (active galactic nuclei), galaxy clusters, and groups of galaxies.

This Year's DSOs (2010-2011)
-**Epsilon Aurigae is part of a special observing campaign through 2011 and will also be included in the DSO list for the 2011/2012 season.
 * Epsilon Aurigae**
 * AAVSO: Epsilon Aurigae
 * NGC 6240
 * Chandra: NGC 6240
 * 3C 321
 * Chandra: 3C 321
 * Centaurus A (NGC 5128)
 * SEDS: Centaurus A
 * Solstation.com: Centaurus A
 * Stephan's Quintet
 * Chandra: Stephan's Quintet
 * NASA APOD: Stephen's Quintet
 * MACSJ0717.5+3745
 * Chandra: MACSJ0717.5+3745
 * Bullet Cluster (1E 0657-56)
 * Chandra: Bullet Cluster
 * NASA APOD: Bullet Cluster
 * Perseus A (NGC 1275)
 * NASA APOD: Perseus A
 * Hubble Heritage: Perseus A
 * SN 2006gy
 * Chandra: SN 2006gy
 * NASA APOD: SN 2006gy
 * SN 1996cr
 * Chandra: SN 1996cr
 * NGC 4603
 * NASA APOD: NGC 4603
 * HyperPhysics: NGC 4603
 * NGC 7771
 * NASA APOD: NGC 7771
 * NGC 2623
 * NASA APOD: NGC 2623
 * Hubble: NGC 2623
 * JKCS041
 * Chandra: JKCS041
 * Messier 77 (NGC 1068)
 * Chandra: Messier 77
 * Universe Today: Messier 77
 * H2356-309
 * Chandra: H2356-309

Basic note sheet for the DSO, intended for use when asked to quickly identify things, or for those new to the event.

Other Information
Although these topics are the focus of this year's competition, there are other topics which you will need to be familiar with.

Galaxies
Galaxies make up a majority of the Astronomy event not covered by the DSO list. Many of the DSO's are galaxies with interesting characteristics. Since this year's competition focuses on active galaxies, many of the DSO's are active.



AGN's and Quasars
AGN's, or Active Galactic Nuclei, are defined as galactic nuclei that emit more electromagnetic radiation than a normal galaxy. This radiation is emitted in a large jet in one direction. In addition, a torus of gas forms around the nucleus perpendicular to the direction of the jet, which can obscure some parts of the galaxy from observers, changing their visual characteristics.

The six main characteristics that define AGN's are: compact angular size, high luminosity, continuum radiation (all types of radiation in the spectrum are emitted), emission lines, variability of emission, and strong radio emission. Quasars, or quasi-stellar radio sources, are similar, as they are galaxies that contain active nuclei. This makes them slightly different than AGN's, but closely related.

Seyfert Galaxy

Seyfert Galaxies are subclasses of active galaxies classified by emission lines of ionized gas. The two main classifications are Type 1 and Type 2. Type 1 Seyferts emit narrow and broad spectral lines, while Type 2 Seyferts only emit narrow lines. Some galaxies can also be classified as numbers between 1 and 2, like 1.5, depending on the relative sizes of the lines. Perseus A is an example of a Type 1.5 Seyfert galaxy.



Other classifications

AGN's and quasars are mainly classified based on the angle that the object is viewed from by an observer on Earth. This is because the angle of the electromagnetic radiation emitted from the nucleus can change how visible the object is. If the emission jet faces away from the observer, the object will appear less active, and vice versa. The diagram at left shows how viewing angle correlates to type of AGN.

AGN's are classified into two large groups, Radio-Quiet AGN's and Radio-Loud AGN's. In Radio-Quiet AGN's, the large jet of radiation faces away from the observer. Seyfert galaxies are Radio-Quiet AGN's. In contrast, Radio-Loud AGN's occur when the jet of radiation faces the observer, and much more activity is apparent. In some cases, the radiation is pointed directly at earth, so an observer can see the radiation jet head-on. There objects are known as Blazars. BL Lacertae and OVV (optically violent variable) Quasars, which are both very variable (OVV Quasars more so), are both Blazars.

Black Holes
Black holes are supermassive objects from which nothing can escape. Since light cannot be emitted, they appear as black spots in space. They can also alter the appearance of surrounding objects because of the high gravitational pull.

Mid-mass black holes, or stellar black holes, have masses at 1.4 to 20 times the Sun. They are very dense and result from the collapse of a large star. Intermediate-mass black holes are thought to be at the center of globular clusters, and they are larger than mid-mass black holes. The largest black holes, supermassive black holes, are usually the centers of galaxies. The center of the Milky Way, Sagittarius A*, is thought to be a supermassive black hole. AGN's are usually supermassive black holes. Supermassive black holes can be over one billion solar masses and less dense than water.

They appear black because their escape velocity is greater than that of the speed of light, and nothing is faster than light.

Supernovae
A supernova is, in short, the explosion of a star. This term can apply to several different types of explosions, though, and so, like many other astronomical terms, there are classifications. Type Ia supernovae are explosions of white dwarves in binary systems that pull mass off of their partner and accumulate enough pressure for a supernova. Type Ib and Ic supernovae are formed when a large star is stripped of its outer hydrogen layers. The Type I supernovae are generally associated with binary systems. Type II supernovae are explosions of supergiant stars that occur when the star fuses iron in its core.

Galaxy Groups and Clusters
Galaxies are usually located close to other galaxies. A galaxy group is the smallest group classification, and it refers to a group of about 30-50 galaxies. The Milky Way is located in the Local Group, along with the Andromeda and Triangulum Galaxies. Galaxy clusters are slightly larger than groups. Although they seem to be held together by gravity, there is no set structure to galaxy clusters. The largest classification is that of galaxy superclusters, which are groups of other groups and clusters. The Milky Way is located in the Virgo (or Local) Supercluster.



Binaries
A binary star is a system of two stars that orbit a common center of gravity, or barycenter. These systems make up nearly 80 percent of all stars in the Milky Way. Binaries and other multiple-star systems can be visual, eclipsing, astrometric, spectroscopic, or a combination of these.


 * Visual binaries appear to the unaided eye to be one star, but can be seen as two through a telescope. An example is Polaris, which is made up of Polaris A ( which is two more stars in itself) and Polaris B.


 * Eclipsing binaries appear to be single stars through a telescope; however, by measuring the brightness of an eclipsing binary, one can determine that the brightness changes over time. This change of brightness is because the plane of these stars' orbit lies along our line of sight. When one star passes in front of the other, it appears as though the "star" gets dimmer. Thus, their light curves reveal occasional dips in luminosity between constant periods due to this eclipse. Epsilon Aurigae, one of the DSO's, is a special eclipsing binary because one of its components is surrounded by a mysterious dust cloud.