STELLAR NURSERIEShttp://www.nasa.gov/multimedia/imagegallery/image_feature_643.html

Molecular Clouds

• Large, dense molecular clouds are very special environments in space. Composed mainly of molecular hydrogen and helium, with small amounts of heavier gases, they are the birth place of new stars and planets.

Stellar Explosion

Supernova

• In star astronomy, the term 'nova' relates to 'new'. A supernova results in the appearance of a bright, new star in the celestial medium. The term 'supernova' was first coined in 1926, by Fritz Zwicky, a Swiss astrophysicist and astronomer. The earliest records on these outer space spectacles date back to the supernova SN 185, sighted and studied in 185 AD.

Supernova

• A supernova refers to a stellar explosion, or explosion of the stars. The very luminous burst of radiation is capable of hiding a whole galaxy in its shadows. It takes quite a few months before the last show of light-and-form extravagance actually fades from sight. During its lifetime, a supernova is observed to radiate energy as much as is associated with the sun. In fact, research reveals that a single supernova is capable of emitting energy that the sun would otherwise radiate over its whole life span!

The Hidden Universe

What is a Stellar Nursery• A “stellar nursery” is romantic way of referring to

a molecular cloud in the process of forming new stars. A molecular cloud is a region of space dense enough with hydrogen atoms that molecules, most commonly H2, or diatomic hydrogen, can form. Molecular clouds may be giant, with 1000 to 100,000 times the mass of the Sun, or smaller, less than a few hundred times the mass of the Sun. These are called giant molecular clouds and small molecular clouds respectively.

Nurseries: New Stars

• As far as we know, star formation occurs exclusively within these molecular clouds, hence the moniker “stellar nursery.” For a molecular cloud to be a stellar nursery, several conditions must be meant. First, the molecular cloud must have enough pockets of sufficient density (“molecular cores”) to provide the raw material to produce stars. Second, the molecular cloud must be subject to agitating forces, such as nearby large stars or supernovae. When a portion of a molecular cloud is lit and ionized by the radiation of a nearby massive star, it is called an HII region.

• Because HII regions are the portions of molecular clouds being most vigorously agitated by outside sources, they are the most likely place to be a stellar nursery. Outside influences are necessary to create a star, because otherwise, a critical density is rarely achieved in a molecular cloud. If density is not sufficient, then gas particles in the cloud just keep orbiting each other forever. Due to an outside influence, such as a supernova shock wave, molecular clouds can condense in localized regions, becoming what is called Bok globules.

Bok Globules

• Bok globules are very dense cores found in stellar nurseries. Typically, they contain about 10-50 solar masses worth of material in an area about a light year across. Bok globules are notable in astronomy because they contain a variety of molecules not usually found in typical sparse interstellar space: molecular hydrogen, carbon oxides, helium, and silicate dust. Sooner or later, it is thought that many Bok globules collapse to form stars, or, more frequently, binary star systems or star clusters. Our Sun is actually thought to be an anomaly in that it has no binary pair.

• Stellar nurseries are eventually destroyed by the stars which create them. The new stars either suck up much of the local material, or blow it away via solar wind. Eventually, these newborn stars might explode in a supernova, triggering the formation of other stars in nearby stellar nurseries.

Orion: Closest Stellar Nebulahttp://apod.nasa.gov/apod/ap040304.html

Fusion and the Sun

The Sun is our Hero

• The enormous importance of the Sun is pretty obvious. It is the center of our solar system and keeps all the planets therein confined in its generous gravitational field. [1] It is also the source of energy for life on earth. Nearly all energy can be attributed directly to the sun's rays. These rays are actually photons or particles of electromagnetic radiation which originate at the sun's intensely heated surface and travel through the vacuum of space to Earth's surface. The process which heats the sun is nuclear fusion.

E=mc2

• This reaction is exemplified in Einstein's famous E=mc2 equation which states that mass can be converted into huge amounts of energy. (the c is the speed of light ~300 million m/s). In nuclear fusion, two atoms must overcome enormous repulsive forces before they can fuse and release massive energy. This requires conditions that are extremely high energy and high density. Thus, the internal temperature of the sun must be kept at nearly 15 million Kelvin.

Right Conditions

• The fusion process in the sun is a delicate one. This is due to the fact that conditions needed to sustain the fusion burn are very extreme. Indeed, outside of nuclear weapons, fusion has made very few appearances on planet Earth. The burning plasma, or ionized gas, of Hydrogen atoms must be contained, otherwise it will blow apart and decrease its density to a level that will not promote fusion. This occurs in stars when the fusion rate becomes too rapid or the core too hot and the star becomes a supernova. This also is exactly what occurs in an atomic bomb.

Solar Fusion

Solar energy - nuclear fusion in the sun - YouTube