Nebulae

Nebula, a cloud of dust and gas inside a galaxy. If the gas glows, Nebulae become visible, or if the cloud reflects starlight or obscures light from more distant objects.

Nebula, the term refers exclusively to interstellar medium. All nebulae that appeared in the Milky way galaxy are forms of interstellar matter. Solid grains of cosmic dust accompanied with gas between the stars. Depending on the spatial situation, temperature and density of the material appearance differs.

Fairy uniform chemical composition that corresponds to the composition of universal atoms, 90 percent hydrogen, and remaining are nitrogen, carbon, oxygen, neon and other elements.

Nebulae are divided into two broad classes : Dark Nebulae and bright nebulae.

Dark Nebulae

Nebulae that appear with irregular shape of dark patches in the sky , known as dark Nebulae. Dark Nebulae are high in density and with cold molecular clouds. Edward Emerson Barnard , the American Astronomer was the first one who record dark nebulae systematically by using long exposure photography. Barnard categorised 370 dark nebulae all over the sky.

Dark Horse Nebula

From Earth’s perspective, dark horse nebula is a large dark nebula. It is also known as Great dark horse. Region of dark nebulae is dark horse that appear as silhouettes because they block out light from shining nebulae or stars behind them.

Bright Nebulae

Dense clouds of gas when compared to dark nebulae within the interstellar medium. Bright Nebulae also called as Galactic or diffuse nebulae. Several subclasses of bright nebulae are

1. Reflection nebulae
2. Planetary nebulae
3. Supernova remnants

Reflection nebula :

It shines due to the reflection of nearby stars. It does not create its own light. Because of the dispersion of blue light efficiently than the red colour, reflection nebulae mostly appears in blue colour. It corresponds to the effect, responsible for the blue colour of the sky.

Planetary Nebula :

Planetary Nebula is the beautiful nebula in the universe. It consists plasma and glowing gas shell . A planetary nebula forms when a stellar core dies. Core of the low madd stars becomes a ” white dwarf ” and also called a ” degenerate dwarf ” and the outer envelope of the star is ejected and the ejected envelop expands away from the central star and creates the nebula. Elements such as oxygen, carbon, helium are present in the planetary nebula.

Supernova remnants :

A Supernova remnants (SNR) is born as the result of violent disruptions of stars and it consists ejected material of the stars. Major source of galactic cosmic rays is supernova remnants. Walter Baade and Fritz Zwicky, suggested the connection between cosmic rays and supernovas.

Nebulae play s crucial role in the chemical evolution of the galaxy. Studying Nebulae helps to understand how a star evolves during its lifetime.