progressed Stars

A star is a round of gas hosted together by its own gravity. Theclosest star to planet is our an extremely own Sun, so us have an example nearbythat astronomers can study in detail. The lessons we learn about theSun can be applied to other stars.

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Diagram mirroring the lifecycles that Sun-likeand huge stars. Click picture for larger version. (Credit: NASA andthe Night sky Network)


throughout most a star"s lifetime, the internal heat and also radiation is providedby nuclear reactions in the star"s core. This phase of the star"s life is referred to as the main sequence.

Before a star will the main sequence, the star is contracting and also its main point is no yet hot or thick enough to start nuclear reactions. So, until it will the main sequence, hydrostatic assistance is noted by the heat produced from the contraction.

At part point, the star will certainly run out of product in its main point for those atom reactions. When the star runs out of nuclear fuel, it comes to the finish of the time on the key sequence. If the star is big enough, it have the right to go with a collection of less-efficient atom reactions to develop internal heat. However, ultimately these reactions will certainly no longer generate enough heat to assistance the star agains its very own gravity and the star will certainly collapse.

Stellar Evolution

A star is born, lives, and also dies, lot like every little thing else in nature. Using monitorings of stars in every phases of your lives, astronomershave created a lifecycle the all stars show up to walk through. Thefate and also life the a star depends generally on it"s mass.


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Hubble photo of the Eagle Nebula, astellar nursery. (Credit: NASA/ESA/Hubble heritage Team)


All stars start their resides from the collapse of material in a giantmolecular cloud. This clouds are clouds that form between the stars andconsist primarily of molecule gas and also dust. Turbulence within the cloudcauses knots to kind which have the right to then collapse under it"s owngravitational attraction. Together the node collapses, the product at thecenter starts to warm up. That hot core is referred to as a protostar and willeventually end up being a star.

The cloud doesn"t collapse right into just one large star, however differentknots of material will each come to be it"s own protostar. This is why theseclouds of product are often called stellar nuseries – they areplaces where many stars form.

As the protostar benefit mass, its main point gets hot and more dense. Atsome point, it will be hot enough and dense enough for hydrogen to startfusing right into helium. It demands to be 15 million Kelvin in the core forfusion to begin. As soon as the protostar start fusing hydrogen, that entersthe "main sequence" step of that is life.

Stars ~ above the key sequence space those that space fusing hydrogen intohelium in their cores. The radiation and also heat native this reaction keepthe force of heaviness from collapsing the star throughout this phase of thestar"s life. This is likewise the longest phase of a star"s life. Ours sunwill spend around 10 billion year on the key sequence. However, a moremassive star offers its fuel faster, and also may only be ~ above the key sequencefor numerous years.

Eventually the core of the star runs out of hydrogen. As soon as thathappens, the star have the right to no longer hold up versus gravity. The innerlayers begin to collapse, i beg your pardon squishes the core, raising thepressure and also temperature in the main point of the star. When the corecollapses, the external layers of product in the star to expand outward.The star increases to larger than it has ever before been – a few hundredtimes bigger! at this suggest the star is referred to as a red giant.

What happens next depends on just how the mass of the star.

The Fate the Medium-Sized Stars


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Hubble photo of planetary nebula IC418,also recognized as the Spirograph Nebula. (Credit: NASA/Hubble HeritageTeam)


When a medium-sized star (up to around 7 times the fixed of the Sun)reaches the red gigantic phase that its life, the core will have enough heatand pressure to reason helium come fuse into carbon, providing the main point abrief reprieve from its collapse.

Once the helium in the main point is gone, the star will burned most the itsmass, forming a cloud that material referred to as a planetary nebula. The main point ofthe star will certainly cool and shrink, leaving behind a small, hot ball dubbed awhite dwarf. A white dwarf doesn"t collapse versus gravity since ofthe press of electrons driving away each other in that is core.

The Fate of substantial Stars


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Chandra X-ray photo of supernova remnantCassiopeia A. The colors show various wavelengths that X-rays beingemitted by the issue that has actually been ejected indigenous the main star.In the center is a ghost star. (Credit: NASA/CSC/SAO)


A red giant star with an ext than 7 time the mass of the sunlight is fatedfor a much more spectacular ending.

These high-mass stars walk through few of the same steps as themedium-mass stars. First, the external layers puffy out right into a huge star,but even bigger, creating a red supergiant. Next, the core starts toshrink, becoming really hot and dense. Then, combination of helium into carbonbegins in the core. When the it is provided of helium runs out, the core willcontract again, but because the core has much more mass, it will end up being hot anddense enough to fuse carbon into neon. In fact, when the supply ofcarbon is supplied up, other blend reactions occur, until the core isfilled v iron atoms.

Up to this point, the fusion reactions placed out energy, permitting thestar come fight gravity. However, fusing iron needs an entry of energy,rather than creating excess energy. Through a core full of iron, the starwill lose the fight versus gravity.

The main point temperature rises to end 100 billion levels as the ironatoms space crushed together. The repulsive force in between thepositively-charged nuclei overcomes the force of gravity, and the corerecoils the end from the love of the star in one explosive shock wave. Inone of the most spectacular events in the Universe, the shock propelsthe material away native the star in a significant explosion dubbed asupernova. The product spews off right into interstellar space.

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About 75% that the massive of the star is ejected into space in thesupernova. The fate that the left-over core relies on its mass. If theleft-over core is about 1.4 to 5 time the fixed of our Sun, it willcollapse right into a spirit star. If the core is larger, it will certainly collapseinto a black color hole. Come turn into a neutron star, a star need to start withabout 7 come 20 time the mass of the Sun before the supernova. Only starswith more than 20 times the fixed of the sunlight will come to be black holes.