Galaxies – everything you need to know about them

The reason for so many stars is that the galaxy has a radius of about 15 kpc and contains a central nuclear bulge with signature black holes (Sagittarius A) located right in the middle. It is the same black hole around which everything in the galaxy, including the solar system, revolves. The Milky Way is one of 50 members of the Local Group, which are bound together by mutual gravity – this group extends for about 3 Mpc.

By far the most interesting galaxies are active galaxies – they have an active galactic nucleus (AGN) that contains a supermassive black hole at the center! Fun fact: the estimated mass of these black holes is about 10^6 – 10^9 times the mass of the black holes that formed during the supernova. In any case, the core has such a large gravitational influence on nearby stars that it forms an accretion disk, in which the stellar matter is accelerated into a black hole, and galactic jets of electrons and positrons are emitted in two beams at almost the speed of light. There are three types of active galaxies – Seyfert galaxies, quasars (they’re really cool) and blazars.

Seyfert galaxies were discovered in 1943 by astronomer Karl Seyfert. They have bright nuclei and emit strongly in the infrared, ultraviolet and X-ray ranges. Discovered in 1964 by Allen Sandage, quasars also emit strong ultraviolet and X-rays, but also emit radio waves. In the images, quasars look like stars and often have a large redshift. One peculiarity of quasars is that they can emit energy thousands of times greater than our galaxy, making them extremely bright and one of the most powerful objects in the entire universe. Blazars are compacted quasars that have high velocity and high energy, but their galactic jets are aimed at us.