Galaxies

GALAXIES

Galaxies are varoius shapes and sizes. Depending upon the shapes, Galaxies are usually classified as spiral, Elliptical or irregular.

Spiral Galaxies are shaped like a disc and have long spiralling arms in which new stars are born.The arms of a spiral galaxy have lots of gas and dust, and they are often areas where new stars are constantly forming. The bulge of a spiral galaxy is composed primarily of old, red stars. Very little star formation goes on in the bulge.

Elliptical Galaxies are ball shaped and consist of older stars Elliptical galaxies have a large range of sizes. The largest elliptical galaxies can be over a million light-years in diameter. The smallest "dwarf elliptical" galaxies are less than one-tenth the size of the Milky Way! Elliptical galaxies have very little gas and dust. Since stars form from gas, little star formation occurs in elliptical galaxies. Most of their stars are old and red. An Irregular Galaxy does not look like either a Elliptical Galaxy or Spiral Galaxy so it would be reffered as a Irregular Galaxy and is very unique in its appearence. Most galaxies fit one of the three previously described types, but about 3% of the galaxies we observe are very different. These so-called "irregular galaxies" do not have a lot of common features. Many of them are the results of galaxy collisions or near misses. One type of irregular galaxy is called a "starburst galaxy." Starburst galaxies shine brightly as many new stars are born in a short period of time. Irregular galaxies are usually found in groups or clusters, where collisions and near-misses between galaxies are common. In a few irregular galaxies, astronomers can't figure out why they look so strange!

Astronomers see Galaxies where ever they look in the sky, when ever they point their most powerful telescopes and most sensitive cameras at a tiny part of the sky only one tenth of the diameter of the moon that seemed to be empty, astronomers can see 10,000 Galaxies there.Astronomers believe there are billions of Galaxies in total.

BARRED GALAXIES: NGC 1365 is one of the most prominent "barred" galaxies in the sky. It is a supergiant galaxy with a diameter of about 200,000 lightyears, seen in the direction of the southern constellation Fornax (The Furnace). It is a major member of the Fornax Cluster of Galaxies. The distance is about 60 million light-years and the recession velocity has been measured as 1632 km/sec.

A massive straight bar runs through this galaxy and contains the nucleus at the centre. It consists mostly of older stars that give a reddish colour to the bar.

The gravitational perturbation from the bar causes interstellar gas and dust clouds to form a pair of spiral arms that extend from the ends of the bar. Young luminous hot stars, born out of the interstellar clouds, give these arms a prominent appearance and a blue colour.

The bar and spiral pattern rotates clockwise, as seen from us. One full turn takes about 350 million years.

FURTHEST GALAXIES! The furthest Galaxies are observed so far away, they are about 13 billion light years away from us, that these Galaxies are so far away the light from them has travelled across the universe for 13 billion years to reach us, So Astronomers are seeing these distant Galaxies

CANNIBAL GALAXY: Cannibal Galaxies, Its a big universe, In most cases, Stars are so far apart that they pass each other harmlessly, But Galaxies in clusters do move around. As a result, some Galaxies collide with each othe. Colliding Galaxies can have an effect on one another.The breaking up of dust clouds, for example can produce alot of radiation and if galaxies in some clusters may be as large as they are because they have swallowed others.The giants are called "cannibal Galaxies" for that reason.

LIST OF NAMED GALAXIES: Milky Way, Andromeda, Bode's Galaxy, Cartwheel Galaxy, Cigar Galaxy, Comet Galaxy, Hoag's Object, Large Magellanic Cloud, Small Magellanic Cloud, Mayall's Object, Pinwheel Galaxy, Sombrero Galaxy, Sunflower Galaxy, Tadpole Galaxy, Whirlpool Galaxy.

Galactic Firsts||~ First ||~ Galaxy ||~ Date ||~ Notes || 3C48 || 1962 1960 || 3C273 was the first quasar with its redshift determined, and by some considered the first quasar. 3C48 was the first "radio-star" with an unreadable spectrum, and by others considered the first quasar. ||
 * First galaxy || Milky Way Galaxy & Andromeda Galaxy || 1923 || Edwin Hubble determined the distance to the Andromeda Nebula, and found that it could not be part of the Milky Way, so defining that Milky Way was not the entire universe, and making the two separate objects, and two galaxies. However, the first galaxies seen would be all of the naked-eye galaxies, but they were not identified as such until the 20th century. ||
 * First radio galaxy || Cygnus A || 1952 || Of several items, then called //radio stars//, Cygnus A was identified with a distant galaxy, being the first of many radio stars to become a //radio galaxy//. ||
 * First quasar || 3C273
 * First Seyfert galaxy || NGC 1068 (M77) || 1908 || The characteristics of Seyfert galaxies were first observed in M77 in 1908, however, Seyferts were defined as a class in 1943. ||
 * First discovered object, later identified to be a cannibalized galaxy || Omega Centauri ||  || Omega Centauri is considered the core of a disrupted dwarf spheroidal galaxy cannibalized by the Milky Way, and was originally catalogued in 1677 as a nebula. It is currently catalogued as a globular cluster. ||
 * First superluminal galactic jet || 3C279 || 1971 || The jet is emitted by a quasar ||
 * First superluminal jet from a Seyfert || III Zw 2 || 2000 ||  ||
 * First spiral galaxy || Whirlpool Galaxy || 1845 || Lord William Parsons, Earl of Rosse discovered the first //spiral nebula// from observing the M51 //white nebula//. ||

THE MILKY WAY:

The Milky Way is simply the common name for the galaxy that encompasses our solar system. The phrase Milky Way came from the band of white light that can be seen across the celestial sphere visible from Earth. This celestial sphere contains a host of various stars and other solar matter. The discovery of the Milky Way is credited to the ancient Greek philosopher Democritus, who was the first person in recorded history to make the assumption that the Milky Way existed and was made up of billions of distant stars. The Milky Way is believed to be more than 13 billion years old, which is estimated to be virtually as old as the entire Universe itself. The Milky Way galaxy is actually just one of billions of galaxies contained within the Universe, although very little is currently known about its seemingly infinite galactic counterparts. The Milky Way galaxy has a whopping circumference of roughly 250-300 thousand light years! Within the main body of the Milky Way there are estimated to be between 200 and 400 billion stars. The Earth’s solar system is believed to exist very close to the Galaxy’s galactic plane, due to the fact that the Milky Way essentially divides the night sky into two virtually equal hemispheres. Scientists now estimate that in roughly three billion years, the Milky Way galaxy will actually collide with the Andromeda Galaxy, which is very slowly working its way towards us at a modest speed of about 1,800 kilometers per minute.