Types of Stars
Stars of all kinds abound in the Universe, ranging from protostars to red supergiants.The stars can be classified according to their mass, and temperature.
Another way of identifying stars is by their spectra (the elements they absorb).Besides their brightness (appearance magnitude), spectral class is very useful to astronomers in detecting the nature of stars.
Seven types of stars exist.As the temperature decreases, O, B, A, F, G, K, and M.A and B are rare, very hot, and very bright.Stars like M are much more common, warmer and darker.
Watch the video below for an overview of the types of stars in the universe.
In spite of the scientific explanations for star colors and sizes, everyone can fully appreciate this reality simply by staring at the night sky.
Certain stars behave like warm, orange objects (such as Betelgeuse in Orion), while others behave like cool, white objects (such as Vega in Lyra).
Stars encircled the Cocoon Nebula in Cygnus.
While stars' colors in the night sky may be pretty to look at, there are fascinating reasons why they differ.The size, color, and life-cycle stage of a star are determined by its age.
The 7 Main Spectral Types of Stars:
Here is a diagram showing the majority of stars (most of them are main sequence stars).Like our own Sun, these stars burn hydrogen to produce helium.
Each type of star is represented here by a diagram illustrating its typical properties.
The classification of stars in the universe (the Atlas of the Universe).
The Morgan Keenan system is known as such.In modern astronomy, Morgan-Keenan (MK) is used as a classification system to classify stars by their spectral type and luminosity level.It was first introduced in 1943 by William Wilson Morgan and Philip C Keenan.
What is the Most Common Type of Star?
It may seem that most stars in the night sky are cool, blue stars that would fall under the B or A class.In our Universe, main-sequence Red dwarf stars are the most common.
Unlike our own Sun, most stars in the universe are cooler and have low masses.Most of the main-sequence Red dwarfs aren't bright enough to be seen with the naked eye from Earth.
The red dwarf burns slowly, so they can live for a long time, as compared to other types of stars.
Proxima Centauri, the closest star to Earth, is a Red dwarf.
However, there are seven types of stars in total, including main-sequence Red dwarfs.This section gives more details about each type of known star.
In the chart below, you will find examples of the colors and temperature of some of the brightest stars in the night sky.
A protostar is the form of a star before it becomes a star.As a protostar, a group of gas is gathered from a large molecular cloud.
Protostars last approximately 100,000 years during their evolution.In time, gravity and pressure increase, forcing the protostar to collapse down.
Its energy is entirely generated by gravitational heating - nuclear fusion reactions have not yet begun.
The Birth of Star (Video)
T Tauri Star:
A T Tauri star is formed at the earliest stage of a star's formation and evolution before it becomes a main-sequence star.
When the star undergoes this phase at the end of its protostar phase, the gravitational pressure holding the star together contains all the star's energy.
Stars of the type T Tauri do not have enough pressure and temperature at their cores to support nuclear fusion, but they are very similar to main-sequence stars; they have about the same temperature, but are brighter since they are larger.
T Tauri stars can have large areas of sunspot coverage, intense X-ray flares, as well as extremely powerful stellar wind speeds.It will take 100 million years for stars to reach the T Tauri stage.
Main Sequence Stars
The main sequence stars are young stars.In their core, the hydrogen (H) is fused with helium (He), a process requiring temperatures of more than 10 million Kelvin.
Almost all stars in the universe are main-sequence stars, including our sun.One-tenth to 200 times the Sun's mass are typical main sequence stars.
The main sequence star is in hydrostatic equilibrium.
During a star's evolution, the inward and outward forces are balanced out, and the star remains spherical.Sizes of stars in the main sequence are determined by their masses, which are defined by the force of gravity pulling them in.
A blue star is generally a hot, O-type star that can be found in star-forming regions, particularly in spiral galaxies around which their light illuminates surrounding dust clouds and gas clouds that typically make these areas appear blue.
Multi-star systems are also often found with blue stars, which are more difficult to predict by their evolution due to both the phenomenon of mass transfer between stars and the possibility of different stars exploding as supernovas at different times.
These stars are mainly characterized by their strong Helium-II absorption lines, and the weaker hydrogen and neutral helium lines of their spectra than a B-type star.
In addition to being hot and massive, blue stars typically have relatively short lives that culminate in violent supernovae events, ultimately leading to black holes or neutron stars.
Red Dwarf Star
Most stars in the universe are red dwarfs.Main-sequence stars but with such low masses that they're much cooler than stars like our Sun.
The cooler state makes them seem faint.However, they do have another advantage.As red dwarf stars are able to mix hydrogen fuel into their core, they are able to conserve their fuel for a long time.
The red dwarf stars in our galaxy can burn for up to 10 trillion years, according to astronomers.The smallest red dwarfs are 0.075 times as massive as the Sun, and they have masses up to half the size of the Sun.
What is a Red Dwarf Star? (Video)
A yellow dwarf is a star of the main sequence possessing a spectral type G and weighing between 0.7 and 1 times the mass of the sun.
The Milky Way has about 10% dwarf yellow stars.Its surface temperature is about 6000 °C and it shines a bright yellow.
The Sun is an example of a G-type star; it, however, is white since all the colors it emits are blended together.
Yellow dwarfs, such as the Sun, are relatively common main-sequence stars.NASA SSDO.
The Sun's visible light is peaks in the green part of the spectrum, even though the entire spectrum is blended to produce white, but the green light component is absorbed by other frequencies both in the Sun and in Earth's atmosphere.
The typical mass of a G star is between 0.84 and 1.15 solar masses. The temperatures of G-type stars are confined to a narrow range between 5,300K and 6,000K.
G-type stars also convert hydrogen into helium in their cores, and they will evolve into red giants when their hydrogen fuel runs out.
The orange dwarf stars are K-type main sequence stars that are roughly between red M-type main sequence stars and yellow G-type main sequence stars in size.
As a result, K stars are particularly interesting in the search for extraterrestrial life, since they emit less ultraviolet radiation (that damages or destroys DNA) than G stars, and they are also stationary on their main sequences for about 30 billion years, compared to only about 10 billion years for the Sun.
Among the largest stars in the universe are supergiant stars.Giants and supergiants are formed when a star runs out of hydrogen and starts burning helium.
As the star's core collapses and gets hotter, its outer layers expand outward as a result.
The Biggest Stars in the Universe (Video)
The stars evolve into red giants as they reach low and medium masses.In contrast, red supergiants are high-mass stars 10+ times the mass of our Sun when their helium is burned.
Despite their enormous size, supergiants consume hydrogen at an incredibly fast rate. Their fuel will be consumed within a few million years.
In Cepheus, Herschel's Garnet star is an example of a red supergiant.The Garnet Star, Mu Cephei, appears garnet red and lies at the edge of the IC 1396 nebula.
A picture of the emission nebula IC 1396 (in Cepheus) showing the red supergiant star Mu Cephei.
A magnitude of *7.6 places Mu Cephei as 100,000 times brighter than our Sun.
The supergiant stars die a young death, detonating as supernovae and destroying themselves.
These stars have luminosity classifications of III and II (bright giant and giant).
There are a variety of stars in different phases of development under this term.The stars are evolved from the main sequence, but otherwise have little in common.
Blue giants are therefore stars found in a particular region of the HR diagram, not a specific type of star.As an example of a blue/white giant star, Alcyone is found in Taurus.
Red giants are more common, but blue giants are much rarer, as they only emerge from more massive stars that are less common, and their lives are usually shorter.Blue giant stars are thought to be big and hot because they tend to be big and hot.
Science refers to blue supergiant stars as OB supergiants; they will generally have luminous classifications of I and spectral classifications of B9 or earlier.
Supergiant blue stars are typically larger than the Sun, but smaller than red supergiant stars, and fall into a mass range of 10 to 100 solar masses.
Usually, type-O and early type-B stars leave the main sequence in a few million years because their mass and high mass burn through their hydrogen supply very quickly.
Blue supergiant stars undergo expansion as soon as heavy elements appear on their surfaces, although in some cases they can convert directly to Wolf–Rayet stars, skipping the "normal" blue supergiant phase.
The star stops generating an outward pressure to counteract the inward pressure pulling it together when it has used the hydrogen in its core.
Continuing the life of the star, hydrogen around its core ignites and causes its size to increase dramatically.Despite being fusion-active, hydrogen is fusing into helium in these stars, but in a shell around an inert helium core.
During the aging phase, the star has become a red giant and is now 100 times larger than its main sequence phase.The fusion process uses additional shells of helium and heavier elements after hydrogen fuel is used up.
After a star runs out of fuel completely, it becomes a white dwarf, leaving only a few hundred million years before it is no longer a red giant.
Supergiant stars have overexpanded as they evolve off the main sequence because they have run out of hydrogen at their cores.
Although they are among the largest stars known based on sheer bulk, these stars are generally not among the most massive or the brightest.
The star Antares in the constellation Scorpius is an example of a red supergiant that is near the end of its lifetime.
Antares, a red supergiant star (Inverse.com), as imagined by an artist.
After fusion, the star's outward light pressure stops and it collapses inward due to gravity.White dwarf stars shine because they were once hot stars, but there are no fusion reactions happening anymore.
White dwarfs just cool down until they become the background temperature of the universe.The process will take hundreds of billions of years, so we haven't seen white dwarfs that cool yet.
Simulation of a neutron star (Wikipedia).
Eventually the core will become a neutron star.A neutron star is a rare type of star made entirely up of neutrons; particles that are more massive than protons yet don't carry an electric charge.
This process is known as neutron degeneracy pressure, and it allows neutron stars to defy their own mass.Neutrons are formed when protons and electrons are crushed together by the gravity of a neutron star.
When the supernova explosion occurs, stars that are even more massive will become black holes instead of neutron stars.
Black holes come in many varieties.
A black hole is a region of heavy density in a star. Cygnus X-1 and Sagittarius A are known examples.
Also called failed stars, brown dwarfs are also known as brown dwarfs.The reason for this is because they are the result of an incomplete fusion.They form just like stars.
Unlike stars, brown dwarfs do not have sufficient mass to ignite and fuse hydrogen inside their cores.For this reason, they do not shine, and their size may be small as well.
Brown dwarfs typically fall into the range of 13 to 80 Jupiter masses, and subbrown dwarfs fall below this range.
Using the diagram below to explain the lifecycle of Sun-like and massive stars can be an excellent tool.There is something fascinating about seeing the transition from nebulae to red supergiants or even to new planetary nebulae as the star-forming process proceeds.
Astronomy and the Life Cycle of a Star (NASA).
In the sky, a double star is two stars which appear near to one another.There are true binary stars (two stars in a stable orbit around one another), and other pairs of stars that appear together as their lines of sight meet.
A binary system consists of two stars that orbit around a common mass center.Approximately half of all stars are found in groups of at least two stars.
Binary stars surround Polaris.
An eclipsing binary is a pair of stars that appear to be a single star, but have varying brightnesses.The variation in brightness is caused by the stars periodically obscuring and enhancing each other.This binary star system is tilted (with respect to our position) so that its orbital plane can be seen from its edge.
X-Ray Binary Star
The X-ray binary stars are unique types of binary stars where one of the stars is collapsed, like a white dwarf, a neutron star, or a black hole.In collapsing stars, matter is stripped from the normal star and falls into the collapsed star, creating X-rays.
Luminosity Varying Variable Stars:
Cepheid Variable Star
Variable Cepheid stars undergo regular changes in size and brightness.When the star grows in size, its brightness decreases, and then the reverse occurs.Cepheid Variables may not be permanently variable; the fluctuations may just be a reflection of the star's instability.Cepheid symbiotic birds include Polaris and Delta Cephei.
Some spiral galaxies that were previously thought to be spiral nebulae were reclassified after Edwin Hubble observed Cepheid variables in some of them.