Nebula

Nebula. Close to 5% of the mass of the galaxy is concentrated in the interstellar matter in the form of diffuse gas and dust, as well as clouds. In particular, the apparent good split the Milky Way in the northern part of the sky due to the inherence in this direction of dense gas and dust clouds, which absorb light of numerous distant vision. The clouds have the appearance of spots of irregular shape, as called diffuse nebulae (from Lat. «Diffusio» – «bleed”).

Note that by the beginning of the XX century. Astronomers call the nebula nonstellar nature of any object, which had the appearance of diffuse (diffuse) light spots. Subsequently, through the use of more powerful telescopes, it was found that many of these nebulae are actually stellar systems or galaxies. Today, the term “nebula” cloud marks of dust and gas, regardless of origin, which is distinguished by its emission or absorption of radiation at the starry sky.

The dust is probably produced in the upper layers of the atmospheres of cool red huge vision that they are almost at the end of its evolutionary path: small particles of solid matter from the gas condenses and eventually fall into interstellar space. The composition of this dust is not exactly clear: believe it or graphite, or various types of silicates. Assume that the interstellar material is 1% of the dust. The main component of the gaseous component of the nebulae is hydrogen – the most common in the universe is a chemical element.

Note: very low-density gas (1 atom in 10 or 100 cm3), which fills the interstellar space in our Galaxy – is also a predominantly hydrogen. Invisible to the naked eye, however, he finds himself, radiating radio wave length of 21 cm.

When observing the sky in the optical telescope found a lot of clouds of gas, which glows, and cosmic dust that covers the light more distant vision. With the help of radio and infrared telescopes clouds failed to learn in detail, because, unlike visible light, radio waves and infrared radiation not absorbed by interstellar dust.
Nebulae are the light and dark. Dark Nebula – a dense molecular gas-dust clouds generally, opaque through absorption of light by dust farther vision. They do not emit light, so look black, and become visible if the contrast with adjacent areas lighter sky. One of the most famous dark nebulae is the Horsehead Nebula in Orion.
Bright nebula are divided into hitters and those that shine themselves. Batters nebula – a gas-dust clouds that do not emit, but only discourage and spread light close to him his sight. Since the gas particles in the composition of the clouds dissipate better short-wave radiation, this type of nebula have a bluish coloring. The famous Pleiades star cluster is surrounded by a bright nebula, that the pictures have a blue-gray color.
Nebulae that glow – it’s the cloud, near which is a young hot dawn, which are capable of their ultraviolet radiation to excite the atoms of gas. The hydrogen atom, absorbing ultraviolet photon, ionizes, and when later joined the electron-proton to form a neutral atom again, absorbed energy is emitted earlier as visible light. So shines a cloud.

One of the most famous nebulae that glow – the Orion Nebula (M42), which is located 1,500 light-years from Earth. It is the brightest in the sky diffuse luminous nebula, which can be seen even with the naked eye. its visible surface is 4 times the area of ??the full moon, and the linear diameter is about AOR light years away. M42 – the closest to the Earth the field of education vision. The main colors of the visible spectrum of the nebula – red emitted by ionized hydrogen, and green emitted by oxygen atoms.

We know that the most massive end their existence dawns supernova explosion. After the explosion is a neutron star or black hole, but dropped out of the shell formed a new astronomical object – a fibrous nebula. The most famous supernova remnant, and at the same time an example of a fibrous nebula is Krabopodobnaya nebula.
In general, the remnants of supernovae – is a relatively young objects, their age is a few hundred to several thousand years. This is due to the fact that over time they are diluted and virtually disappear.
“Nebula” – so named at the end of the XVIII century. W. Herschel gave a weak obscure objects whose appearance reminded him of the planetary disk of Neptune and Uranus, which he often watched. And although today it is known that planetary nebulae have a different nature and in no way associated with the planets, historically, that is the name of them stuck.

Planetary nebula – a final stage in the evolution of the red giant. Ejected shell of dawn (approximately 0.1 – 0.2 solar masses), expands spherically in the form of a nebula in outer space, and its naked core becomes a white dwarf.