Indeed the centre of the Milky Way galaxy is invisible in ordinary light because the interstellar dust in that direction is so thick. They show only small evidence for young stars, dust or gas. They are very different in size ranging from giant ellipticals with masses of about 1 million million times that of the Sun to dwarf ellipticals with masses closer to those of the globular clusters. A radio image of M82, an irregular galaxy which is interacting with the spiral galaxy M81. The interaction has triggered a wave of star formation, known as a starburst.
Some galaxies are neither ellipsoidal nor are they spirals.
Some galaxies show evidence for the generation of enormous amounts of energy from the vicinity of their nucleus. These are often strong radio emitters and often show complex lobe structure extending for millions of light years. The presence of black holes at the centres of these objects is thought necessary by many astronomers to explain their nature. Because they are the brightest objects known in the universe it is not surprising that quasars are the objects that have been traced out furthest from us. The furthest known are so far away that the light we see coming from them must have originated when the Universe was only one tenth of its present age.