K-type stars are of particular interest in the search for extraterrestrial life, since they emit markedly less UV radiation that damages or destroys DNA than G-type stars on the one hand, and they remain stable on the main sequence for up to about 30 billion years, as compared to about 10 billion years for the Sun. Moreover, K-type stars are about four times as common as G-type stars, making the search for exoplanets a lot easier. The largest stars in the Universe are supergiant stars.
Giants and supergiants form when a star runs out of hydrogen and begins burning helium. Low and medium-mass stars then evolve into red giants. Supergiants are consuming hydrogen fuel at an enormous rate and will consume all the fuel in their cores within just a few million years. Supergiant stars live fast and die young, detonating as supernovae; completely disintegrating themselves in the process.
Stars with luminosity classifications of III and II bright giant and giant are referred to as blue giant stars. The term applies to a variety of stars in different phases of development. They are evolved stars that have moved from the main sequence but have little else in common. Therefore blue giant simply refers to stars in a particular region of the HR diagram rather than a specific type of star. Blue giants are much rarer than red giants, because they only develop from more massive and less common stars, and because they have short lives.
Some stars are mislabelled as blue giants because they are big and hot. Blue supergiant stars are scientifically known as OB supergiants, and generally have luminosity classifications of I, and spectral classifications of B9 or earlier. Blue supergiant stars are typically larger than the Sun, but smaller than red supergiant stars, and fall into a mass range of between 10 and solar masses.
Typically, type-O and early type-B main sequence stars leave the main sequence in only a few million years, since they burn through their supply of hydrogen very quickly due to their high masses. When a star has consumed its stock of hydrogen in its core, fusion stops and the star no longer generates an outward pressure to counteract the inward pressure pulling it together.
A shell of hydrogen around the core ignites continuing the life of the star but causes it to increase in size dramatically. In these stars, hydrogen is still being fused into helium, but in a shell around an inert helium core. The aging star has become a red giant star and can be times larger than it was in its main sequence phase. When this hydrogen fuel is used up, further shells of helium and even heavier elements can be consumed in fusion reactions.
Red supergiant stars are stars that have exhausted their supply of hydrogen at their cores, and as a result, their outer layers expand hugely as they evolve off the main sequence.
Stars of this type are among the biggest stars known in terms of sheer bulk, although they are generally not among the most massive or luminous.
Antares , in the constellation Scorpius , is an example of a red supergiant star at the end of its life. An artists rendering of Antares, a red supergiant star Inverse.
When a star has completely run out of hydrogen fuel in its core and it lacks the mass to force higher elements into fusion reaction, it becomes a white dwarf star. The outward light pressure from the fusion reaction stops and the star collapses inward under its own gravity.
A white dwarf will just cool down until it becomes the background temperature of the Universe. This process will take hundreds of billions of years, so no white dwarfs have actually cooled down that far yet.
Neutron stars are the collapsed cores of massive stars between 10 and 29 solar masses that were compressed past the white dwarf stage during a supernova explosion. A simulated view of a neutron star Wikipedia. The remaining core becomes a neutron star. A neutron star is an unusual type of star that is composed entirely of neutrons; particles that are marginally more massive than protons, but carry no electrical charge.
The intense gravity of the neutron star crushes protons and electrons together to form neutrons. If stars are even more massive, they will become black holes instead of neutron stars after the supernova goes off. While smaller stars may become a neutron star or a white dwarf after their fuel begins to run out, larger stars with masses more than three times that of our sun may end their lives in a supernova explosion.
The dead remnant left behind with no outward pressure to oppose the force of gravity will then continue to collapse into a gravitational singularity and eventually become a black hole , with the gravity of such an object so strong that not even light can escape from it. There are a variety of different black holes.
Stellar-mass black holes are the result of a star around 10 times heavier than the Sun ending its life in a supernova explosion, while supermassive black holes found at the center of galaxies may be millions or even billions of times more massive than a typical stellar-mass black hole. Brown Dwarfs are also known as failed stars. This is due to the result of their formation. Brown Dwarfs form just like stars.
However, unlike stars, brown dwarfs do not have sufficient mass to ignite and fuse hydrogen in their cores. Typically, brown dwarf stars fall into the mass range of 13 to 80 Jupiter-masses, with sub-brown dwarf stars falling below this range. Stellar Classification Chart Hertzsprung—Russell diagram.
The following diagram os a fantastic visual reference to use when describing the lifecycle of Sun-like and massive stars. It is fascinating to see the transition between the nebulae stages of the star-forming process to a red supergiant or even a new planetary nebula. A double star is two stars that appear close to one another in the sky.
Some are true binaries two stars that revolve around one another ; others just appear together from the Earth because they are both in the same line-of-sight. The powerhouse of the star converts more than 4 million tons of solar material into energy every second, Plait said.
Altogether, Plait estimated that the sun has lost a total of 10 24 tons of material over its 4. While that sounds like a lot, it's only about 0. The sun is classified as a G-type main-sequence star, or G dwarf star, or more imprecisely, a yellow dwarf. Actually, the sun — like other G-type stars — is white, but appears yellow through Earth's atmosphere. Stars generally get bigger as they grow older. In about 5 billion years, scientists think the sun will start to use up all of the hydrogen at its center.
The sun will puff up into a red giant and expand past the orbit of the inner planets, including Earth. The sun's helium will get hot enough to burn into carbon, and the carbon will combine with the helium to form oxygen. These elements will collect in the center of the sun.
Later, the sun will shed its outer layers, forming a planetary nebula and leaving behind a dead core of mostly carbon and oxygen — a very dense and hot white dwarf star, about the size of the Earth.
While the sun is typical in most respects, it does have one quality that stands out from the majority of stars — it is a loner. Most stars have a companion , with some part of a triple or even a quadruple system. With a great big Universe out there, populated with countless stars, astronomers have been able to see examples of stars in all shapes, sizes, metal content and ages.
According to their system of classification, the Sun is known as a yellow dwarf star. So the Sun is at the higher end of this group. The official designation is as a G V star. Stars in the this classification have a surface temperature between 5, and 6, K, and fuse hydrogen into helium to generate their light. They generally last for 10 billion years. Some are newly forming, others are in their middle ages, and others are nearing the end of their lives.
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