Active Galactic Nuclei…. You may not know what they are, but you have to admit that they sound pretty crazy! Many galaxies have bright centers due to stars bunched up around a super massive black hole. Active galactic nuclei (AGN) are the super bright cores of distant galaxies. AGN have supermassive black holes that are actively accreting a lot of matter. This in fall of matter creates heat, turns the region around the black hole into plasma, and emits copious amounts of light. The image above is what the active nucleus of NGC 5141 looks like in X-rays! The bright yellow center means lots of x-rays are being emitted, and therefore this region must be very hot and active. AGN are so bright that we can see ones (with good telescopes) that are as far as 12 billion light years away! When we look at AGN, we are most likely seeing light from very large and compact galaxies that existed in the beginning of the universe. There are three main types of AGN: Syefert, Blazars and Quasars. The differences lie in the type of radiation emitted. Astronomers think that there may only be one "type" of AGN, and they look different because we are viewing them at different angles. Seyferts, Blazars and Quasars will be discussed more in future ADYK.
Image credit: Radomski, J. et al. 2003, AJ 587, 117
