A star is a ball of gas organized together by its very own gravity. The closestly star to planet is our really own Sun, so we have actually an example adjacent that astronomers can study in detail. The lessons we learn around the Sun have the right to be used to other stars.

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A star"s life is a constant struggle versus the force of gravity. Gravity constantly works to try and cause the star to collapse. The star"s core, but is really hot which creates pressure within the gas. This press counteracts the force of gravity, placing the star into what is referred to as hydrostatic equilibrium. A star is okay as long as the star has actually this equilibrium in between gravity pulling the star inwards and pressure pushing the star outwards.

Diagram mirroring the lifecycles that Sun-like and massive stars. Click photo for bigger version. (Credit: NASA and also the Night sky Network)

During most a star"s lifetime, the interior heat and also radiation is listed by atom reactions in the star"s core. This phase of the star"s life is referred to as the main sequence.

Before a star get the key sequence, the star is contracting and its core is no yet hot or dense enough to begin nuclear reactions. So, until it reaches the main sequence, hydrostatic support is detailed by the heat created from the contraction.

At some point, the star will run out of material in its main point for those atom reactions. As soon as the star runs out of nuclear fuel, it comes to the end of that time top top the main sequence. If the star is big enough, it deserve to go v a collection of less-efficient nuclear reactions to create internal heat. However, at some point these reactions will no longer generate adequate heat to assistance the star agains its very own gravity and the star will collapse.

Stellar Evolution

A star is born, lives, and also dies, lot like whatever else in nature. Using monitorings of stars in all phases of your lives, astronomers have created a lifecycle the all stars appear to walk through. The fate and life the a star depends generally on it"s mass.

Hubble image of the Eagle Nebula, a stellar nursery. (Credit: NASA/ESA/Hubble heritage Team)

All stars begin their lives from the collapse of product in a giant molecular cloud. These clouds room clouds that kind between the stars and consist mostly of molecular gas and dust. Disturbance within the cloud reasons knots to type which can then collapse under it"s very own gravitational attraction. As the node collapses, the product at the center starts to warmth up. That hot core is referred to as a protostar and will eventually become a star.

The cloud doesn"t collapse into just one big star, yet different knots of product will each end up being it"s own protostar. This is why these clouds of product are often dubbed stellar nuseries – lock are places where countless stars form.

As the protostar gains mass, its main point gets name is and more dense. At part point, it will certainly be hot enough and also dense enough for hydrogen to start fusing right into helium. It demands to be 15 million Kelvin in the core for fusion to begin. Once the protostar start fusing hydrogen, that enters the "main sequence" step of that is life.

Stars ~ above the key sequence space those that room fusing hydrogen right into helium in your cores. The radiation and also heat native this reaction store the pressure of heaviness from collapsing the star during this step of the star"s life. This is also the longest step of a star"s life. Our sun will spend about 10 billion years on the main sequence. However, a much more massive star supplies its fuel faster, and may only be on the key sequence for countless years.

Eventually the main point of the star runs out of hydrogen. When that happens, the star can no longer host up versus gravity. Its inside layers start to collapse, which squishes the core, boosting the pressure and also temperature in the main point of the star. If the main point collapses, the outer layers of material in the star to increase outward. The star expands to bigger than it has ever before been – a few hundred time bigger! in ~ this allude the star is called a red giant.

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

The Fate the Medium-Sized Stars

Hubble image of planetary nebula IC 418, additionally known together the Spirograph Nebula. (Credit: NASA/Hubble heritage Team)

When a medium-sized star (up to about 7 times the mass of the Sun) will the red giant phase the its life, the core will certainly have sufficient heat and also pressure to reason helium come fuse right into carbon, giving the core a quick reprieve indigenous its collapse.

Once the helium in the main point is gone, the star will shed most the its mass, developing a cloud of material called a planetary nebula. The main point of the star will cool and also shrink, leave behind a small, warm ball called a white dwarf. A white dwarf doesn"t collapse versus gravity since of the pressure of electrons fending off each other in that is core.

The Fate of huge Stars

A red large star with an ext than 7 time the fixed of the sunlight is fated because that a more spectacular ending.

Chandra X-ray photo of supernova remnant Cassiopeia A. The color show various wavelengths of X-rays gift emitted by the matter that has been ejected native the main star. In the center is a ghost star. (Credit: NASA/CSC/SAO)

These high-mass stars go through several of the same measures as the medium-mass stars. First, the external layers swell out into a large star, yet even bigger, forming a red supergiant. Next, the main point starts to shrink, becoming very hot and also dense. Then, fusion of helium into carbon begins in the core. As soon as the supply of helium runs out, the core will contract again, but because the core has more mass, that will become hot and also dense sufficient to fuse carbon right into neon. In fact, once the supply of carbon is offered up, other fusion reactions occur, till the main point is filled with iron atoms.

Up to this point, the fusion reactions put out energy, allowing the star come fight gravity. However, fusing iron requires an input of energy, fairly than developing excess energy. Through a core full of iron, the star will lose the fight against gravity.

The core temperature rises to end 100 billion degrees as the iron atoms are crushed together. The repulsive force between the positively-charged nuclei overcomes the force of gravity, and the main point recoils out from the love of the star in one explosive shock wave. In among the most spectacular occasions in the Universe, the shock propels the product away native the star in a remarkable explosion referred to as a supernova. The material spews off into interstellar space.

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About 75% of the massive of the star is ejected into space in the supernova. The fate that the left-over core depends on that mass. If the left-over core is around 1.4 to 5 time the fixed of our Sun, it will certainly collapse into a ghost star. If the main point is larger, it will certainly collapse right into a black hole. To turn right into a spirit star, a star need to start with about 7 come 20 time the massive of the Sun before the supernova. Just stars with an ext than 20 time the fixed of the sunlight will come to be black holes.