How can A Stars is growth

Spitzer will present significant information on the structure and growth of stars and the circumstellar medium (surrounding the star). The discovery and characterization of circumstellar disks of gas and dust, signs of extra-solar planetary systems is one of the most important scientific goals of the Spitzer mission

Molecular gas

The giant molecular clouds are composed primarily of hydrogen, are the reserve materials from which stars form. 

These clouds, scattered by the interstellar medium of our Milky Way, contain enough gas and dust to form hundreds of thousands of stars like the Sun Spitzer study the temperature and density of molecular clouds to characterize the physical and chemical compositions of which are formed protesters.

Star pattern

The stars are born inside cocoons of dust and dense molecular gas, and are mostly undetectable in visual light. The near-infrared light at wavelengths of a few microns, can pass through the veil of dust. Spitzer used his camera to short wavelengths to study the formation and evolution of young stellar objects in the first million years of life. The Spitzer observations also reveal what fraction of stars form in clusters.

                                        

Circumstellar disk

A substantial fraction of Spitzer observing time will be devoted to the study of circumstellar disks of dust (surrounding the star). It is thought that these flattened disks around young stars are characteristic of the evolution and formation of planetary systems. Protoplanetary disks contain gas and dust and supply the materials from which planetary systems form. Planetary dust disks of second-generation discs ("debris") represent a later stage in evolution, where most of the gas has dissipated. These discs are composed mostly of small dust grains presumably formed from collisions between small planetesimals and large rocky bodies.

 Spitzer will be able to detect and characterize circumstellar disks of nearby stars, providing key information on the formation of planetary systems. The detection of faint disk at visible light is extremely difficult because the star is much brighter. But the relative difference between the brightness of the star and the disk decreases in the infrared, where Spitzer made the observations. Spitzer will study hundreds of nearby stars to determine the frequency of these discs. Also use imaging and spectroscopy to characterize the spatial structure and composition of the disks. These data will be valuable to determine the frequency and nature of planetary systems like ours.

Dwarfs and Low Mass

Although the bright, massive stars which dominate the night sky, most of the stellar mass in galaxies is in stars of low luminosity and low mass. These stars live for billions of years, but are weaker and cooler than our Sun, and are therefore difficult to detect in visible light. Spitzer detected these objects in the infrared. Special attention will be the discovery and characterization of brown dwarfs. These objects are too small to sustain thermonuclear reactions, which are those that define a star, and therefore these objects radiate primarily in the infrared. The existence of brown dwarfs was only a theory when Spitzer was. Since the mid 90's, telescopes and astronomical surveys such as 2MASS , have identified a few hundred of these objects with temperatures below 2000 K. Spitzer will detect thousands of brown dwarfs, including Aquinas only slightly larger than Jupiter, and thus providing a large enough number for statistical analysis.

Star Clusters

The Spitzer observations in this area will focus primarily on open (or galactic), gravitationally bound systems of thousands of young stars that are typically found in the plane of our galaxy. Clusters are thought to harbor faint brown dwarfs. Spitzer conducted a search of these weak members of clusters (previously invisible) detecting masses of more than 10 times the mass of Jupiter.

Evolved Stars

Spitzer conducted several research programs of further evolutionary states of stars. Once most of the thermonuclear fuel is exhausted after tens of billions of years, a star like the Sun will enter a rapidly changing its fate determined by the initial mass of the star. During the last stages of his life, the typical star-shaped material ejected gas from its outer layers, through periodic explosions (such as a nova), or through violent cataclysmic explosion (supernova). Spitzer will study the material ejected by the star that form planetary nebulae, providing information on the temperature and composition of the eject and the mass loss rate of the star. The gas and dust ejected by dying stars is an important constituent of the interstellar medium and its study is fundamental to understanding not only how stars die but how stars are born of the next generation.

Interstellar Medium

Sandwiched between the stars is a tenuous interstellar medium (ISM) composed of dust grains and gas atoms and molecules. The powder absorbs ultraviolet and visible light, which causes increases in temperature and re-emit light in the infrared. Moreover, most important spectral lines produced by the gas in the ISM are also found in the infrared. Spitzer exploited this to carry out spectroscopic studies of the interstellar medium. These investigations are the studies on water, ice and organic molecules. The Spitzer observations in the near infrared will map the central regions of the Milky Way, providing important information in visible light is obscured by heavy dust concentrations found in the central regions of the galaxy.