An Introduction to Active Galactic Spectra
Active Galaxies are one of the stunning powerhouses of the universe radiating immense radiation at nearly all wavelengths that can be seen throughout the entire universe. Unlike spiral or irregular type galaxies, which emit ionized Hydrogen radiation at sharp, narrow peaks, Active Galaxies radiate them at a much broader and stronger flux range. A typical Active Galactic Spectrograph may look like the following:
At first glance, it is easy to mistake it as a spectrum coming from a Gas cloud region from any spiral galaxy. However, a closer look shows that the lines are extremely stretched out which indicates the presence of temperatures exceeding ¹⁰⁸ kelvins at its core. However, at such immense temperatures, Hydrogen atoms should be completely stripped off from their shells which means Hydrogen lines in the spectra is utterly impossible.
However, a second alternative is the bulk motion of gases at several thousand kilometers per second! These are very large velocities indeed and imply that large amounts of kinetic energy are tied up in the gas motions.
The above diagram represents the spectral emission diagram (SED) of the active galaxy 3C 273. Unlike any normal galaxy, this one has a flux density, that is extremely high at the X-ray region and the infrared regions of the electromagnetic spectrum. This hints that in addition to containing nearly a hundred billion stars, these galaxies contain something, something extremely powerful radiating from a very small, dense region. Such explanations seem to be possible only if we allow the possibility of a gigantic, monstrous Black Hole harboring at the Galaxy’s center.
The extreme Radial velocities could be explained by huge bulks of matter spiraling into the black hole at nearly the speed of the light. Due to this rapid infalling of matter, the formation of extremely strong magnetic fields surrounding a black hole is not an unlikely phenomenon at all. The magnetic fields will then spiral up electrons and eject Infrared radiation perpendicular to the direction of the electronic motion (Synchrotron Radiation). All of these contribute to the extraordinary spectrograph we receive from Active Galaxies.
Active Galaxies, based upon their spectral nature can be divided into the following classes:
a) Seyfert Galaxies
b) Quasars
c) Radio Galaxies
d) Blazars
e) Starburst galaxies (non-active class)
Most of the Spectra that we receive from Active Galaxies have enormous redshifts. This means that they are moving away from us at comparable speeds to the speed of light. As our universe experiences an accelerated expansion owing to Dark Energy, the velocity of recession increases with distance. This means that Active Galaxies are mostly faraway objects. Whether these galaxies were predominantly common in the early universe or it’s a phase most galaxies experience through remains a question to this day.
