Presentation on theme: "Objectives: 1.Explain current theories of how galaxies form, and change over time. 2.Know the characteristics of the milky way galaxy. 3.Compare and contrast."— Presentation transcript:
Objectives: 1.Explain current theories of how galaxies form, and change over time. 2.Know the characteristics of the milky way galaxy. 3.Compare and contrast different types of galaxies including; barred, spiral, elptical, and irregular galaxies.
Galaxy Formation Galaxy formation is hypothesized to occur as a result of tiny quantum fluctuations in the aftermath of the Big Bang. They formed as a consequence of the growth of these primordial fluctuations, which are small changes in the density of the universe in a confined region.
Galaxy Formation The universe was very violent in its early epochs, and galaxies grew quickly, evolving by accretion of smaller mass galaxies. The result of this process is left imprinted on the distribution of galaxies in the nearby universe.
Formation of disk galaxies commonly called spiral galaxies. they are very thin, rotate rapidly, and often show spiral structure.
merger events in the evolution of galaxies Our own galaxy has a tiny satellite galaxy (the Sagittarius Dwarf Elliptical Galaxy) which is currently gradually being ripped up and "eaten" by the Milky Way. It is thought these kinds of events may be quite common in the evolution of large galaxies.
Galaxy mergers and the formation of elliptical galaxies The most massive galaxies in the sky are giant elliptical galaxies. All elliptical galaxies probed so far have super massive black holes in their center. In the Local Group, the Milky Way and M31 (the Andromeda Galaxy) are gravitationally bound, and currently approaching each other at high speed. Astronomers now see elliptical galaxies as some of the most evolved systems in the universe
The Milky Way Galaxy The Milky Way is a barred spiral galaxy 100,000– 120,000 light-years in diameter containing 200– 400 billion stars. The very center is marked by an intense radio source which is likely to be a super massive black hole. The rotational period is about 200 million years at the position of the Sun. The Galaxy as a whole is moving at a velocity of 552 to 630 km per second, depending on the relative frame of reference. It is estimated to be about 13.2 billion years old
The Milky Way Galaxy The rotational period is about 200 million years at the position of the Sun. The Galaxy as a whole is moving at a velocity of 552 to 630 km per second, depending on the relative frame of reference. It is estimated to be about 13.2 billion years old
Local Group The Local Group is the group of galaxies that includes Earth's galaxy, the Milky Way. The group comprises more than 54 galaxies, including dwarf galaxies.
Spiral galaxies Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are surrounded by a much fainter halo of stars, many of which reside in globular clusters.
Barred Galaxies A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. The bar is thought to act as a mechanism that channels gas inwards from the spiral arms, funneling the flow to create new stars.
dwarf galaxy A dwarf galaxy is a small galaxy composed of up to several billion stars.
Irregular galaxy An irregular galaxy is a galaxy that does not have a distinct regular shape. they are often chaotic in appearance. Most irregular galaxies were once spiral or elliptical galaxies but were deformed by disorders in gravitational pull
Elliptical Galaxies Appear spherical from all angles, due to the fact that they are not rotating. They are the oldest and most stable galaxies in the universe.