Intermediate spiral galaxy

An intermediate spiral galaxy is a galaxy that is in between the classifications of a barred spiral galaxy and an unbarred spiral galaxy. It is designated as SAB in the galaxy morphological classification scheme. By definition, a galaxy is a congregation of stars held together by gravity. The first intermediate spiral galaxy discovered is the Milky Way, by Galileo, in 1610. He was the first person with a telescope powerful enough to make such a discovery. Before Galileo, it was thought that all bright objects in the sky were either the planets in the Solar System, moons, comets, or stars. Until the beginning on the twentieth century, astronomers did not know the size of the Universe, but speculated it to be about as big as the Milky Way. In 1920, at the National Academy of Science, there was a big debate between Harlow Shapley and Heber D. Curtis on whether nebulae are small globular clusters surrounding the Milky Way, or separate galaxies located farther away. Nothing was resolved at the debate; neither side was able to provide conclusive evidence to prove their side correct over their opponent. In 1923, Edwin Hubble resolved the matter with a photograph that he took of the Andromeda Galaxy. What he found in his photograph was a very bright light source pulsing at a certain rate, a Cepheid variable, located outside the Milky Way. This can be used to determine the distance to it. Hubble proved that the Universe was full of galaxies, and disproved that the Milky Way was the extent of the Universe. There are many types of galaxies in the Universe, elliptical, barred spiral galaxies; they vary in shape and size, but on average spiral galaxies are the most abundant.

A galaxy starts out as a giant cloud of cold gas. The cloud of gas must be close to absolute zero, if the gas cloud is too hot, the atoms will have too much kinetic energy, and gravity will not be able to condense the cloud. When a cloud reaches a mass of about 10⁹−10¹¹ times the mass of the Sun, the gas cloud will collapse under gravity. For an intermediate spiral galaxy to form, the gas cloud must be rotating, and as the gas coalesces, the gas cloud will flatten out to form a disk shape. The mass remaining constant, to comply with the physical laws which govern the conservation of angular momentum, its rotational velocity will speed up. At the very center of the galaxy, the gas will condense so much under gravitational pressure that a supermassive black hole will form. All spiral galaxies have a black hole at the center of their galaxy, called the galactic nucleus, which range from 10⁶ to 10⁹ times the mass of the Sun.

...
Wikipedia