The increasingly hot core also pushes the outer layers of the star outward, causing them to expand and cool, transforming the star into a red giant.
Hydrogen is still available outside the core, so hydrogen fusion continues in a shell surrounding the core. Deprived of the energy production needed to support it, the core begins to collapse into itself and becomes much hotter. When a star has fused all the hydrogen in its core, nuclear reactions cease. In general, the larger a star, the shorter its life, although all but the most massive stars live for billions of years. Although extreme stars such as these are believed to have been common in the early Universe, today they are extremely rare - the entire Milky Way galaxy contains only a handful of hypergiants. Hypergiants emit hundreds of thousands of times more energy than the Sun, but have lifetimes of only a few million years. On the other hand, the most massive stars, known as hypergiants, may be 100 or more times more massive than the Sun, and have surface temperatures of more than 30,000 K. Despite their diminutive nature, red dwarfs are by far the most numerous stars in the Universe and have lifespans of tens of billions of years.
The smallest stars, known as red dwarfs, may contain as little as 10% the mass of the Sun and emit only 0.01% as much energy, glowing feebly at temperatures between 3000-4000K. The outflow of energy from the central regions of the star provides the pressure necessary to keep the star from collapsing under its own weight, and the energy by which it shines.Īs shown in the Hertzsprung-Russell Diagram, Main Sequence stars span a wide range of luminosities and colors, and can be classified according to those characteristics. Stars are fueled by the nuclear fusion of hydrogen to form helium deep in their interiors. Our Sun will stay in this mature phase (on the main sequence as shown in the Hertzsprung-Russell Diagram) for approximately 10 billion years. Main Sequence StarsĪ star the size of our Sun requires about 50 million years to mature from the beginning of the collapse to adulthood. Observations with NASA's Chandra X-ray Observatory provided a likely explanation: the interaction between the young star's magnetic field and the surrounding gas causes episodic increases in brightness. When observers around the world pointed their instruments at McNeil's Nebula, they found something interesting - its brightness appears to vary. In January 2004, an amateur astronomer, James McNeil, discovered a small nebula that appeared unexpectedly near the nebula Messier 78, in the constellation of Orion. In some cases, the cloud may not collapse at a steady pace. Not all of this material ends up as part of a star - the remaining dust can become planets, asteroids, or comets or may remain as dust. Smith (University of Arizona)Īs the cloud collapses, a dense, hot core forms and begins gathering dust and gas. The observations of Eta Carinae's light echo are providing new insight into the behavior of powerful massive stars on the brink of detonation.Ĭredit: NOAO, AURA, NSF, and N. Three-dimensional computer models of star formation predict that the spinning clouds of collapsing gas and dust may break up into two or three blobs this would explain why the majority the stars in the Milky Way are paired or in groups of multiple stars.
Known as a protostar, it is this hot core at the heart of the collapsing cloud that will one day become a star.
As the cloud collapses, the material at the center begins to heat up. Turbulence deep within these clouds gives rise to knots with sufficient mass that the gas and dust can begin to collapse under its own gravitational attraction. A familiar example of such as a dust cloud is the Orion Nebula. Stars are born within the clouds of dust and scattered throughout most galaxies. Consequently, the study of the birth, life, and death of stars is central to the field of astronomy. Moreover, stars are responsible for the manufacture and distribution of heavy elements such as carbon, nitrogen, and oxygen, and their characteristics are intimately tied to the characteristics of the planetary systems that may coalesce about them. The age, distribution, and composition of the stars in a galaxy trace the history, dynamics, and evolution of that galaxy. Stars are the most widely recognized astronomical objects, and represent the most fundamental building blocks of galaxies.