Which stellar type is brightest

For instance, if two stars are the same size but one is twice as hot as the other in kelvin, the former would be 16 times as luminous as the latter. Astronomers generally measure the size of stars in terms of the radius of our sun. For instance, Alpha Centauri A has a radius of 1.

Stars range in size from neutron stars, which can be only 12 miles 20 kilometers wide, to supergiants roughly 1, times the diameter of the sun. The size of a star affects its brightness. Specifically, luminosity is proportional to radius squared.

For instance, if two stars had the same temperature, if one star was twice as wide as the other one, the former would be four times as bright as the latter. Astronomers represent the mass of a star in terms of the solar mass , the mass of our sun.

For instance, Alpha Centauri A is 1. Stars with similar masses might not be similar in size because they have different densities. For instance, Sirius B is roughly the same mass as the sun, but is 90, times as dense, and so is only a fiftieth its diameter. Stars are spinning balls of roiling, electrically charged gas, and thus typically generate magnetic fields.

When it comes to the sun, researchers have discovered its magnetic field can become highly concentrated in small areas, creating features ranging from sunspots to spectacular eruptions known as flares and coronal mass ejections. A recent survey at the Harvard-Smithsonian Center for Astrophysics found that the average stellar magnetic field increases with the star's rate of rotation and decreases as the star ages.

The metallicity of a star measures the amount of " metals " it has — that is, any element heavier than helium. Three generations of stars may exist based on metallicity. Astronomers have not yet discovered any of what should be the oldest generation, Population III stars born in a universe without "metals.

When a number of these died, they released more heavy elements, and the youngest Population I stars like our sun contain the largest amounts of heavy elements. Stars are typically classified by their spectrum in what is known as the Morgan-Keenan or MK system. There are eight spectral classes, each analogous to a range of surface temperatures — from the hottest to the coldest, these are O, B, A, F, G, K, M and L.

Each spectral class also consists of 10 spectral types, ranging from the numeral 0 for the hottest to the numeral 9 for the coldest. Stars are also classified by their luminosity under the Morgan-Keenan system. The largest and brightest classes of stars have the lowest numbers, given in Roman numerals — Ia is a bright supergiant; Ib, a supergiant; II, a bright giant; III, a giant; IV, a subgiant; and V, a main sequence or dwarf.

A complete MK designation includes both spectral type and luminosity class — for instance, the sun is a G2V. The structure of a star can often be thought of as a series of thin nested shells , somewhat like an onion. A star during most of its life is a main-sequence star, which consists of a core, radiative and convective zones , a photosphere, a chromosphere and a corona. The core is where all the nuclear fusion takes places to power a star.

In the radiative zone, energy from these reactions is transported outward by radiation, like heat from a light bulb, while in the convective zone, energy is transported by the roiling hot gases, like hot air from a hairdryer. Massive stars that are more than several times the mass of the sun are convective in their cores and radiative in their outer layers, while stars comparable to the sun or less in mass are radiative in their cores and convective in their outer layers.

Intermediate-mass stars of spectral type A may be radiative throughout. After those zones comes the part of the star that radiates visible light, the photosphere , which is often referred to as the surface of the star. After that is the chromosphere, a layer that looks reddish because of all the hydrogen found there. In fact most of the nearby sun-like stars are in the south! The ones in the northern hemisphere tend to be fainter, but if you can find the constellation Draco , some of its brighter stars are the Solar-type.

Stars which are much more massive than our Sun burn hotter but for much less time, living and dying within a few million years. An example in the sky is the bright star Spica in the constellation of Virgo. Stars which are much less massive than our Sun burn cooler, and live longer — potentially for hundreds of billions of years. When a star runs of hydrogen fuel in its core, it has to adjust and find alternate ways to power itself — one of the ways it does this is to start burning hydrogen outside the core and this makes the star swell up.

The result is a cool, puffy red giant star. Because these stars are so large, they tend to be bright, and we can see several in our skies. As the hydrogen is used up, these stars can start burning helium and then heavier elements in their cores, heating up and producing blue and yellow supergiants and hypergiants. 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. A binary star is a system of two stars that rotate around a common center of mass. About half of all stars are in a group of at least two stars.

An eclipsing binary is two close stars that appear to be a single star varying in brightness. The variation in brightness is due to the stars periodically obscuring or enhancing one another.

This binary star system is tilted with respect to us so that its orbital plane is viewed from its edge. X-ray binary stars are a special type of binary star in which one of the stars is a collapsed object such as a white dwarf, neutron star, or black hole.

As matter is stripped from the normal star, it falls into the collapsed star, producing X-rays. Cepheid variables are stars that regularly pulsate in size and change in brightness. Stars that are closer to Earth, but fainter, could appear brighter than far more luminous ones that are far away.

The solution was to implement an absolute magnitude scale to provide a reference between stars. To do so, astronomers calculate the brightness of stars as they would appear if it were Another measure of brightness is luminosity, which is the power of a star — the amount of energy light that a star emits from its surface. It is usually expressed in watts and measured in terms of the luminosity of the sun. For example, the sun's luminosity is trillion trillion watts.

One of the closest stars to Earth, Alpha Centauri A , is about 1. To figure out luminosity from absolute magnitude, one must calculate that a difference of five on the absolute magnitude scale is equivalent to a factor of on the luminosity scale — for instance, a star with an absolute magnitude of 1 is times as luminous as a star with an absolute magnitude of 6.

While the absolute magnitude scale is astronomers' best effort to compare the brightness of stars, there are a couple of main limitations that have to do with the instruments that are used to measure it. First, astronomers must define which wavelength of light they are using to make the measurement.

Stars can emit radiation in forms ranging from high-energy X-rays to low-energy infrared radiation. Depending on the type of star, they could be bright in some of these wavelengths and dimmer in others. To address this, scientists must specify which wavelength they are using to make the absolute magnitude measurements.