Galaxy

Measuring extra-terrestrial distances has always been a feat for mankind. By being able to measure the universe there have been fundamental changes in the understanding of astronomy. Tycho Brahe’s supernova and Edwin Hubble’s Cepheid’s have meant we are able to measure the size of the universe to a fairly accurate scale. The problem with these conventional methods is that there are no methods of measuring objects with a red shift z of >1.7. For years astronomers tried to find a way to measure the distance of active galactic nuclei as they span the whole visible universe.

The active galactic nuclei or central core of a galaxy produces huge quantities of radiation through nuclear fusion; they often produce more energy than the rest of the galaxy. There are many different types of AGN such as; quasars, starburst galaxies, blazars, Seyfert galaxies and radio loud galaxies. AGN are extremely efficient at producing light as up to 10% of mass approaching the event horizon is converted into light energy, the sun on the other hand has 0.7% efficiency. Due to their brightness AGN can be used to view how the universe was near it beginning, at around 1 billion years old, when it was around 1/6th the size it is now.

At the heart of every AGN there is a supermassive black hole, and is the main power source of the AGN. This black hole is surrounded by high velocity gas clouds that produce broad emission lines. It is known that there is a relationship between the broad line emitting region (BLR) and the AGN’s continuum luminosity. The BLR size is determined by finding how much of the gas surrounding the black hole can be ionised by the central source. This happens to obey the inverse square law. This means that the radius r is directly proportional to the root of the luminosity of the AGN √L.