How can stars be classified

Massive stars also run out of hydrogen sooner than smaller stars do. Our Sun has been a main sequence star for about 5 billion years and will continue on the main sequence for about 5 billion more years.

Very large stars may be on the main sequence for only 10 million years. Very small stars may last tens to hundreds of billions of years. As a star begins to use up its hydrogen, it fuses helium atoms together into heavier atoms such as carbon. A blue giant star has exhausted its hydrogen fuel and is a transitional phase. When the light elements are mostly used up the star can no longer resist gravity and it starts to collapse inward.

The outer layers of the star grow outward and cool. The larger, cooler star turns red in color and so is called a red giant. Eventually, a red giant burns up all of the helium in its core. What happens next depends on how massive the star is. A typical star, such as the Sun, stops fusion completely.

A white dwarf will ultimately fade out. A star that runs out of helium will end its life much more dramatically. When very massive stars leave the main sequence, they become red supergiants. Unlike a red giant, when all the helium in a red supergiant is gone, fusion continues.

Lighter atoms fuse into heavier atoms up to iron atoms. Creating elements heavier than iron through fusion uses more energy than it produces so stars do not ordinarily form any heavier elements. When there are no more elements for the star to fuse, the core succumbs to gravity and collapses, creating a violent explosion called a supernova.

Its core collapses and it gets hotter, resulting in the outer layer to expand outwards. Stars that are either low or medium in mass evolved into red giants. During periods of slow fusion, the star can contract itself and become a blue supergiant.

This color is usually present when temperatures are spread over a small surface area, making them hotter. Oscillations between red and blue can also occur. These stars are very rare, their spectral types are O, B, and A.

Their temperatures are usually around They have a mass of 2 to that of our sun and last around 10 to million years. There are a wide variety of stars termed blue giants. Many stars with luminosity classifications of III and II are referred to as blue giants merely out of preference. However, the true blue giants have temperatures above These stars are also rare, spectral type OB.

They have a mass of around 20 to 1. Scientifically known as OB supergiants, these stars have luminosity classifications of I, and spectral classifications of B9. They are smaller than red supergiants and usually leave their main sequence in only a few million years. Because of their mass, they quickly burn their hydrogen supplies. Some stars evolve directly into Wolf-Rayet stars, jumping over the normal blue supergiant phase. These stars have a prevalence of around 0.

They have temperatures of around 3. They have a mass of about 0. They are much smaller than red supergiants and much less massive. The RBG-branch is the most common, with hydrogen still being fused into helium, but in a shell around an inert helium core. The red-clump giants use helium and fuse it into carbon while the AGB branch burns their helium in a shell around a degenerate core of carbon and oxygen.

Some examples are: Aldebaran, Arcturus. They have a mass of about 10 to 40 that of our sun and live around 3 to million years. These stars have exhausted their supplies of hydrogen at their cores. Because of this, their outer layers expand hugely as they evolve off the main sequence. They are among the biggest stars in the universe, though they are not among the most massive or luminous.

Some red supergiants which still can create heavy elements eventually explode as type-II supernovas. Some examples are: Antares, Betelgeuse, Mu Cephei. They have temperatures of around 8. These stars no longer produce energy to counteract their mass. Theoretically, they cannot exceed 1. They have temperatures of around They have a mass of about 1. Neutron stars are basically the collapsed cores of massive stars that were compressed beyond the white dwarf stage during a supernova explosion.

They consist of neutron particles that are a bit more massive than protons with no electrical charge. They can further collapse into black holes if they have more than 3 solar masses. Only neutron stars that have high spin rates and more than 3 solar masses may resist this process.

These stars are more hypothetical in nature. They are theorized to be white dwarfs that have radiated away all their leftover heat and light.

Since white dwarfs have relatively high life spans, no black dwarfs had enough time to form yet. If such stars would form, this would occur after our Sun will die. Small stars may become white dwarfs or neutron stars but stars with high masses become black holes after a supernova explosion. Since the remnant has no outward pressure to oppose the force of gravity, it will continue to collapse into a gravitational singularity and eventually become a black hole.

Such an object is so strong that not even light can escape from it. Examples of such objects are: Cygnus X-1, Sagittarius A. Failed stars are celestial objects that do not have sufficient mass to ignite and fuse hydrogen gas. Therefore, they do not shine. Astronomers now often use constellations in the naming of stars. The International Astronomical Union, the world authority for assigning names to celestial objects, officially recognizes 88 constellations.

Usually, the brightest star in a constellation has "alpha," the first letter of the Greek alphabet, as part of its scientific name. The second brightest star in a constellation is typically designated "beta," the third brightest "gamma," and so on until all the Greek letters are used, after which numerical designations follow.

A number of stars have possessed names since antiquity — Betelgeuse , for instance, means "the hand or the armpit of the giant" in Arabic. It is the brightest star in Orion, and its scientific name is Alpha Orionis. Also, different astronomers over the years have compiled star catalogs that use unique numbering systems. The Henry Draper Catalog, named after a pioneer in astrophotography, provides spectral classification and rough positions for , stars and has been widely used of by the astronomical community for over half a century.

The catalog designates Betelgeuse as HD Since there are so many stars in the universe, the IAU uses a different system for newfound stars. Most consist of an abbreviation that stands for either the type of star or a catalog that lists information about the star, followed by a group of symbols.

The J reveals that a coordinate system known as J is being used, while the and are coordinates similar to the latitude and longitude codes used on Earth. In recent years, the IAU formalized several names for stars amid calls from the astronomical community to include the public in their naming process.

The IAU formalized 14 star names in the "Name ExoWorlds" contest , taking suggestions from science and astronomy clubs around the world. Then in , the IAU approved star names , mostly taking cues from antiquity in making its decision. The goal was to reduce variations in star names and also spelling "Formalhaut", for example, had 30 recorded variations. However, the long-standing name "Alpha Centauri" — referring to a famous star system with planets just four light years from Earth — was replaced with Rigel Kentaurus.

A star develops from a giant, slowly rotating cloud that is made up entirely or almost entirely of hydrogen and helium. Due to its own gravitational pull, the cloud behind to collapse inward, and as it shrinks, it spins more and more quickly, with the outer parts becoming a disk while the innermost parts become a roughly spherical clump.

According to NASA, this collapsing material grows hotter and denser, forming a ball-shaped protostar. When the heat and pressure in the protostar reaches about 1. Nuclear fusion converts a small amount of the mass of these atoms into extraordinary amounts of energy — for instance, 1 gram of mass converted entirely to energy would be equal to an explosion of roughly 22, tons of TNT.

The life cycles of stars follow patterns based mostly on their initial mass. These include intermediate-mass stars such as the sun, with half to eight times the mass of the sun, high-mass stars that are more than eight solar masses, and low-mass stars a tenth to half a solar mass in size.

The greater a star's mass, the shorter its lifespan generally is. Objects smaller than a tenth of a solar mass do not have enough gravitational pull to ignite nuclear fusion — some might become failed stars known as brown dwarfs. An intermediate-mass star begins with a cloud that takes about , years to collapse into a protostar with a surface temperature of about 6, F 3, C.

After hydrogen fusion starts, the result is a T-Tauri star , a variable star that fluctuates in brightness. This star continues to collapse for roughly 10 million years until its expansion due to energy generated by nuclear fusion is balanced by its contraction from gravity, after which point it becomes a main-sequence star that gets all its energy from hydrogen fusion in its core.

The greater the mass of such a star, the more quickly it will use its hydrogen fuel and the shorter it stays on the main sequence. After all the hydrogen in the core is fused into helium, the star changes rapidly — without nuclear radiation to resist it, gravity immediately crushes matter down into the star's core, quickly heating the star.

This causes the star's outer layers to expand enormously and to cool and glow red as they do so, rendering the star a red giant. Helium starts fusing together in the core, and once the helium is gone, the core contracts and becomes hotter, once more expanding the star but making it bluer and brighter than before, blowing away its outermost layers.

After the expanding shells of gas fade, the remaining core is left, a white dwarf that consists mostly of carbon and oxygen with an initial temperature of roughly , degrees F , degrees C. Since white dwarves have no fuel left for fusion, they grow cooler and cooler over billions of years to become black dwarves too faint to detect. Our sun should leave the main sequence in about 5 billion years.

A high-mass star forms and dies quickly. These stars form from protostars in just 10, to , years. While on the main sequence, they are hot and blue, some 1, to 1 million times as luminous as the sun and are roughly 10 times wider.

When they leave the main sequence, they become a bright red supergiant, and eventually become hot enough to fuse carbon into heavier elements. After some 10, years of such fusion, the result is an iron core roughly 3, miles wide 6, km , and since any more fusion would consume energy instead of liberating it, the star is doomed, as its nuclear radiation can no longer resist the force of gravity. When a star reaches a mass of more than 1.

The result is a supernova.