Solar System: Related topic

The Galaxy

The Universe is estimated to contain 200 billion galaxies.

There are various kinds of galaxies in our universe which are formed by millions of stars, dusts and gases in the outer space. Our solar system is located in the milky way of the galaxy in a spiral shape. Ther ara millions of galaxies in the shape of spiral, ellipse and non-uniform or irregulars in the universe. These galaxies are located far away from one another in the outer space

Galaxies come in three main types: ellipticals, spirals, and irregulars. A slightly more extensive description of galaxy types based on their appearance is given by the Hubble sequence. Since the Hubble sequence is entirely based upon visual morphological type, it may miss certain important characteristics of galaxies such as star formation rate (in starburst galaxies) and activity in the core (in active galaxies).^[7]

^{Types Of Galaxies}

Types of galaxies according to the Hubble classification scheme. An Eindicates a type of elliptical galaxy; an S is a spiral; and SB is a barred-spiral galaxy.

The elliptical galaxies

The most massive galaxies in the sky are giant elliptical galaxies. Their stars are on orbits that are randomly oriented within the galaxy (i.e. they are not rotating like disk galaxies). They are composed of old stars and have little to no dust. All elliptical galaxies probed so far have supermassive black holes in their center, and the mass of these black holes is correlated with the mass of the elliptical galaxy. They are also correlated to a property called sigma which is the speed of the stars at the far edge of the elliptical galaxies. Elliptical galaxies do not have disks around them, although somebulges of disk galaxies look similar to elliptical galaxies. One is more likely to find elliptical galaxies in more crowded regions of the universe.

Example of elliptical galaxies:

ESO 325-G004, a typical elliptical galaxy

The spiral galaxies

The key properties of disk galaxies, which are also commonly called spiral galaxies, is that they are very thin, rotate rapidly, and often show spiral structure. One of the main challenges to galaxy formation is the great number of thin disk galaxies in the local universe. The problem is that disks are very fragile, and mergers with other galaxies can quickly destroy thin disks.

Examples of spiral galaxies: