There are many, many different kinds of stars. Stars are usually grouped by color (temperature helps define a star's color). These colors are represented by letters. These letters are O (blue), B (bluish-white), A (white), F (yellowish-white), G (yellow), K (orange) and M (red). Sometimes it is extended with L (reddish-brown), T (methane brown dwarf), and Y (ultracool brown dwarf).
Despite the titles of the colors for spectral types, they are not the true color of the star. The true colors (approximation) are shown on the upper-right. The false colors are in the lower-right.
O-type stars are the rarest stars known. They are well over 53,540°F and they are the hottest, heaviest, and brightest stars. They live for just 1,000,000 years and they expand to a red supergiant (or hypergiant if heavy enough)! Then they become a supernova (or hypernova if heavy enough)! Then they become Black Holes later.
B-type stars are the second rarest stars and they are 17,540 to 53,540°F, the second rarest stars. They live for 10,000,000 years and they become a red supergiant and they go supernova. They will be either a Neutron Star or a Black Hole.
A-type stars are 13,040 to 17,540°F and they are the third rarest stars. After having a 100,000,000 year life they become red bright giants and they become a bright nova (more commonly known as a planetary nebula). Even though they look like white, they are actually the bluest stars.
F-type stars are neutral stars. They are 10,340 to 13,040°F and they are 3 times brighter than the Sun. At least, if the Sun was an F-type, Mars would be a little bit too hot to survive. They live for 1,000,000,000 years old, and then they become red giants, and the red giant explodes to a planetary nebula. The nebula (nova) evaporates, and the remains is an old, small, dim, hot white dwarf star. Then the white dwarf will become a black dwarf.
G-type stars are the third most common stars. Believe me, even though the sun is very hot, it is not a very hot star because brown dwarves are not stars and G-type stars are 8,981 to 10,340°F. The Sun is a G2 V star and is hotter and brighter than most G-type stars. G-type stars will become red giants when they are 10,000,000,000 years old and then they will become planetary nebulas. The nebula will evaporate and there a white dwarf is left. In hundreds of trillions of years, the white dwarf will become a black dwarf.
K-type stars are nice stars because they are 6,200 to 8,981°F. They are also the second most common stars. Orange giants like Pollux will be a red giant; the Sun will be an orange giant and later a red giant. They are the second most common stars and they are dimmer than the Sun. There are no dying K-type stars in the universe because the universe is 13,800,000,000 years old and these types live for 100,000,000,000 years and later they will be a red subgiant. The red subgiant will explode to a subnova. The remains of a subnova are called a white dwarf. The white dwarf will later be a black dwarf.
Red Dwarves are the most common stars by far. However, they are so dim that it is harder than it seems to find one. M-types may be the smallest and coldest of stars, but they make up for size too. There isn't any such thing as Red Giants, Supergiants and Hypergiants (but even they don't compete with Blue Hypergiants for mass) which span larger than Saturn's orbit. VY Canis Majoris is a very notable example. As a red hypergiant, it's duty is to be incredibly huge. Reddish-orange stars are all M-type stars that are 3,860 to 6,200°F. Red Dwarves have super long life, at least 1,000,000,000,000 years. Later they will reach the blue dwarf stage and sooner the blue dwarf will explode to a dwarfnova. The dwarfnova will evaporate, leaving a white dwarf behind. The white dwarf will become a black dwarf so many hundreds of trillions of years later. (or maybe quadrillions)! Red Subgiants are evolved K-types; Red Giants are evolved G and F-types; Red Supergiants are evolved A, B, and O types; and Red Hypergiants are evolved O type stars. Hypernovas are like supernovas, but release tons and tons of gamma rays. So much in fact, even at a 7,500 light-year distance, we aren't safe. Oh, and Blue Hypergiants do this too. So this is why they are far away, thank God.
L-type dwarves are a very cold kind of red dwarf and the first stage of the brown dwarf life. It's a young brown dwarf, which will decay into a T-dwarf billions of years later. Lithium is present in its spectrum, but this isn't why it's letter is L. It's because L isn't used in astronomy and it's the letter before M. They are 1,880 to 3,860°F cold, extremely ice cold for a star. Sadly, there is no conventional color description for stars of spectral types M6.5 to L9.9. It could be either red-brown or purple-red. Both are pretty acceptable. Red-Brown because it's in between red and brown stars, and Purple-Red because it follows a pattern with the RGB color spaces. Though L, T, and Y-types aren't official Harvard spectral classes, they should really be because the supergiant star V838 Monocerotis possibly has a spectrum similar to L-types. So it may be possible for there to be L-type giants and supergiants. On the smaller side, there are the stars 2MASS J05325346+8246465 and SDSS J141624.08+134826.7, which are L-type subdwarfs. Subdwarfs are stars that are smaller than a main-sequence. So, like other true stars, L-types have a wide variety of sizes!
T-type stars have methane in their atmosphere, which is odd considering its rarity in the universe. They are the evolved and cooled form of L-dwarves and are 800 to 1,880°F, which is extremely freezing for a star. T-types are truly Brown Dwarfs, half-way in between stars and planets. And Brown Dwarves, despite their name, aren't actually brown. They are actually magenta due to Sodium and Potassium ions in their atmospheres. Brown dwarves are so light, they can't fuse Hydrogen, meaning they shouldn't be considered stars, but they can fuse Deuterium (if more than 13x heavier than Jupiter) and Lithium (if over 65x heavier than Jupiter)
Y-type stars are ultraultracold, -63 to 800°F, and can fuse Deuterium. The Y-types include sub-brown dwarves and ultracool brown dwarves. The coldest star was a Y-type, at -63.4°F, far colder than the second coldest which was 206.6°F. It also very hard to tell the difference between a very big planet and a very small Brown Dwarf.
P-type stars are unbelievably cold at -220 to -63°F. They are so cold, they are not even stars! They are massive planets that look like too big to be planets. They are not even evolved Y-type stars, they are just planets! Even the most massive planet, HAT-P-2b is too heavy to be a planet but too light to be a Brown Dwarf, But, to see if it is a planet or a brown dwarf, let's see what is closer to. But guess what? A planet is an answer. I just put this on the list to compare poor Jupiter.
There are more classes than just O, B, A, F, G, K, M, L, T, and Y.
|X||209,240 to 509,840°F||Purple Star. Although stars realistically come in all colors, the human eye isn't sensitive to indigo or violet light nor are the two colors black body colors, which is the reason why there aren't any purple stars. However, some hyper-inaccurate size comparisons may have purple stars and if that's the case, either get your eyes checked or don't buy the info and stick with fact.|
|N||100,000 to 900,000°F||Navy-Blue Star. It has a huge amount of strange gas, suppressing the luminosity of the star, recoloring it from blue to navy-blue aka very dark blue.
This gas has confirmed to exist only in TWZ-1938C Universe.
|W||58,940 to 359,540°F||Wolf-Rayet Star. Extremely hot and massive O-type hypergiant stars, the hottest and heaviest stars ever. They don't fuse Hydrogen but instead fuse Helium or other elements. They are often confused with LBVs and Blue Hypergiants.|
|LBV||53,540 to 98,540°F||Luminous Blue Variable. Very large and bright Blue Hypergiants that are extremely luminous, blue, and are S Doradus variables. Duh. Most of them are invisible to the naked eye due to how far away they are.|
|S||3,860 to 7,539°F||A Red or Orange Giant that has Zirconium Oxide in its spectrum. They are, for some reason, different from M and K types because of this Zirconium Oxide. That's just messed up. But then again, these are the rules of stars.|
|C||3,860 to 5,030°F||A Red Giant or infrequently, a Red Dwarf that has excess carbon in its atmosphere and has more carbon than regular stars. Usually, these stars are very red, the reddest of the stars! Unless of course, you count L-types as stars.|
|D||6,200 to 180,032°F||A White dwarf. The remnants of a red giant's nova. They are about the size of Earth, give or take. But they are roughly the same weight as The Sun, so they are very dense. A piece of White Dwarf one cm long, wide and high can weigh as much as 10,000 kg! That's like, uh..., an elephant or two. Even though they are called "white" dwarfs, their stellar type could reach from K to O.|
|n0||89,540 to 1,800,000,000,030°F||A neutron star. Made of stable degenerate Neutronium, extremely dense, weighing 1 to 3 times the mass of the Sun, but 3.8 to 48.2 km wide, making them the smallest and densest of stars. A mL of Neutronium can weigh 379,400,000,000 kg. That's the weight of 37,940,000 to 80,698,380 elephants. But where are you gonna get that many elephants if there are only 740,000 elephants on Earth?|
|Φ||1010,000,000,000°F||A Red Hole! Red holes are actually a red version of the black hole. Another difference is that black holes are cold; red holes are usually at least a trialogue degrees fahrenheit!|
|Ψ||100 to 100,000°F||A Green Hole! This term was coined by UniversePoker777 when he found out about the Greenholeverse and its green holes. Green Holes are stars that a black hole becomes if they lose from 0 to 2,200 pounds of mass in a billion years. But the Green Holes are billions, or even trillions of light years away.|
|Ω||-459.6666666666669 to -459.666669°F||A Black Hole! It's a region of spacetime that absolutely nothing, not even light, can escape. This is why it's black, not to be racist or anything. I'm referring to black so blackly, Vantablack doesn't compare (Black Holes absorb 100% of light, Vantablack only absorbs 99.965%)! And Black Holes are not cosmic vacuum cleaners at all. Why do people think of
that?! Maybe because it "sucks" you in before you get spaghettified (the actual term of dying in a black hole). There are three main parts of a black hole: the inner and outer event horizon and the singularity. The outer event horizon is the "warped" part you can see. It shows you the true power of the weakest force in the universe (gravity). The inner event horizon is black part and the part that determines the "size" of a black hole. You will never escape it at all (but in the case of a stellar-mass one, you'd be spaghettified before you enter it). The singularity is the center of the black hole. It literally has zero sizes, but all the mass of the black hole is compressed in there. So it's a VERY big thing in an infinitely small package. But black holes are losing their mass at a VERY slow rate. It's called "Hawking radiation", named after, guess who? An atheist named Stephen Hawking. Now the currently living black holes will live for 10^68 to 10^92 years, determined by this big ugly formula: tev = 5,120πG2M03∕ħc4. M0 is the mass for your Black Hole, so if you made a black hole, well, don't. When black holes die, they explode. Formula? The good ol' E = mc2, in which m is the mass of your hole.
|QS||6,746°F||Quasi-stars. They are stars with Black Holes (Ω) for their cores. They probably existed in the very early history of the Universe. UY Scuti, the current largest known star (1,708 solar radii), and even the made-up Shadron Soul (3,283) and VY Masses Majoris (6,734), hail in comparison to the Quasi-star, its minimum size is about 7,187 solar radii and it's maximum is over 10,000 solar radii.|
The letter classes are divided further by the numbers 0-9. 0 means hottest, 9.9 means the coldest. For example, our star is G2 V. It is a G-type, meaning it's yellow. And it has a 2, meaning it's really hot for a G-type. It also has 'V', meaning 'Main-Sequence', a luminosity class. Note: Some luminosity classes have classes. So that's classifying classes of classes.
There are also luminosity classes for stars.
-IX: Infinitygiant: Brighter and heavier Finalgiant.
-VIII: Finalgiant: Brighter and heavier Archgiant.
-VII: Archgiant: Brighter and heavier Absolutegiant.
-VI: Absolutegiant: Brighter and heavier Megagiant.
-V: Megagiant: Heavier and brighter Omnigiant.
-IV: Omnigiant: Heavier and brighter Xenogiant.
-III: Xenogiant: More extraordinary Ultragiant.
-II: Ultragiant: Metamassive and metaluminous Metagiant. The term is fake and was made up by 1917 Darwin (the page's creator)
-I: Metagiant: Hyperluminous and supermassive Hypergiant. Term is fake and was coined in hyperinaccurate size comparison.
0: Hypergiant: Extremely luminous and massive Supergiant.
W (or W R) (prefix): Wolf-Rayet Star: Extremely massive O-type star.
- W N: spectrum with lots of Nitrogen and Helium
- W N/C: intermediate between W N and W C stars
- W C: spectrum with lots of Carbon
- W O: A spectrum with lots of Oxygen
I: Supergiant: A very large star bigger than a Giant, but lighter than a Hypergiant.
- Ia: Luminous Supergiant: A very bright Supergiant, and one of the Largest of stars
- Iab: Intermediate Luminous Supergiant: Medium-Bright Supergiant
- Ib: Less Luminous Supergiant: Dimmer Supergiant, but still very bright
II: Bright Giant: A Bright giant. Duh.
III: Giant: A large star
IV: Subgiant: Bigger than a Main-Sequence, smaller than a giant
V: Main-Sequence: Ordinary young star.
VI (or sd (prefix)): Subdwarf: Similar to Main-Sequence, but smaller
D (prefix) (or VII): White Dwarf: A remnant of a red giant's planetary nebula.
- D A: Hydrogen-rich atmosphere
- D B: Helium-rich atmosphere, indicated by neutral helium
- D O: Helium-rich atmosphere, indicated by ionized helium
- D Q: Carbon-rich atmosphere
- D Z: metal-rich atmosphere
- D C: no strong spectral lines
- D X: spectral lines are insufficiently clear
n0 (prefix): Neutron Star: A remnant of a red supergiant's supernova.
- PS (prefix): Pulsar: A highly magnetized, rapidly rotating Neutron star that emits radio waves that we can listen to. When one was first heard, people thought they were listening to an alien distress call!
- MR (prefix): Magnetar: A neutron star with an extremely powerful magnetic field, over a 1,000,000,000,000,000 times stronger than Earth's magnetic field. They are super-magnetic, and so far 21 are known to humans.
- Q (prefix): Gray Hole: Sort of like a mix between a Black Hole (region of spacetime in which matter and light can only get in, but not out) and a White Hole (hypothetical region of spacetime in which matter and light can get out, but not in), as it is a hypothetical compact object the size of a black hole, but has an exotic state of matter. Light can get out (but not in) and matter can get in (but can't get out).
Exotic Star: A compact star that has an exotic state of matter.
- q (prefix): Quark Star: A hypothetical star 5 km in radius and made entirely out of quarks. They are most likely much smaller than Neutron Stars and in terms of weight, they are heavier than Gray Holes but lighter than Black Holes. A Quark Star that contains Strange Matter is called a Strange Star.
- p (prefix): Preon Star: A hypothetical star made entirely out of preons. They are 5 cm in radius, far smaller than Quark Stars and in terms of weight, they are heavier than Quark Stars, but lighter than Black Holes.
- Q (prefix): Gray Hole: Gray Holes are both neutron stars and exotic stars. Fun to know, right? They are much lighter than Black Holes, but much heavier than White Holes.
- e (prefix): Electroweak Star: A hypothetical star that's gravitational collapse is protected by radiation pressure made from electroweak burning. They should be heavier than Quark Stars, but lighter than Preon Stars.
- b (prefix): Boson Star: A hypothetical star made entirely out of bosons. However, such an object would have to be made of bosons that at least contains mass, as bosons are massless.
- P (prefix): Planck Star: A hypothetical star that's energy density is around the Planck density, 5.155 x 1093 g/cm3, or 5.155 x 10^78 Pg/cm3, which is 13,587,243,015,287,295,730,100,158,144,039,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 times denser than Neutronium!
Hole: A region of spacetime with wonky gravitational effects, such as the warping of time and light.
- Ω: Black Hole: A region of spacetime in which nothing, not even light can escape. They aren't cosmic vacuum cleaners nor are they wormholes. Ω: Black Hole: A region of spacetime in which nothing, not even light can escape. They aren't cosmic vacuum cleaners nor are they wormholes.
- 1a: Micro Black Hole: Micro Black holes are small black holes that pertain a mass less than a planet's. The upper limit to its Schwarzschild radius is about 10 cm, but they are generally depicted to be microscopic in size.
- 1b: Planetary Mass Black Hole: Planetary Mass Black Holes are Black Holes the mass of a planet or small brown dwarf, and are generally a few meters across.
- 2: Stellar-Mass Black Hole: Stellar Mass black holes are black holes the mass of a star. This class of black holes can be divided into two subclasses. The subclass that scientists generally call stellar mass black holes is 2b, the larger of the two classes. These black holes are formed via supernovae or hypernovae when the iron core of the star surpasses the Tolman-Oppenheimer-Volkoff limit, which is about 3 solar masses. The smaller of the two classes, 2a, refers to a black hole that pertains a mass between the smallest star and 3 solar masses, black holes that pertain a stellar mass lower than the Tolman-Oppenheimer-Volkoff limit.
- 3: Intermediate Mass Black Hole: Intermediate-mass black holes are black holes that are in between the size of a stellar-mass black hole and a supermassive black hole. They pertain a mass in between 300 and a million solar masses and are formed when stellar mass black holes consume enough matter.
- 4: Supermassive Black Hole: Supermassive black holes are large black holes in the millions to billions of solar masses, and are formed when stellar mass or intermediate mass black holes consume enough matter. Most spiral or elliptical galaxies have a supermassive black hole in the center. The supermassive black hole in the center of the Milky Way is Sagittarius A*.
- 5: Ultramassive Black Hole: The term Ultramassive black holes refers to extraordinarily large black holes, ones that exceed 20 AU in size and exceed a billion solar masses and reaching a trillion solar masses. The most famous example of one would be TON 618, at 60 billion solar masses.
- 6: Metamassive Black Hole: Metamassive black holes are beyond intensely heavy, from a trillion to a quadrillion solar masses. They are so extraordinary, more than anyone can imagine!
- 7: Xenomassive Black Hole: Xenomassive black holes are so heavy, they are as heavy as a soda bring drunk by a black hole! They have a quadrillion to a quintillion solar masses.
- 8: Hypermassive Black Hole: Hypermassive black holes are nothing, just heavy. They have a quintillion to a SEXTILLION solar masses!
- 9: Sub-Exophage Black Hole: They are beyond intermediate-super-ultra-meta-xeno-hyper massive black holes! WATCH OUT! THEY HAVE A SEXTILLION TO A SEPTILLION SOLAR MASSES!
- 10+: Exophage Black Hole: They are so heavy, they have a septillion solar masses and higher! They don't exist in our universe because they have an intense diameter of 311,500,000,000 light years and the Universe is only 160,000,000,000 light years.
- Ω: Infinite-Mass Black Hole: These black holes have ∞ solar masses, but there is another universe called the Holeverse where all these nonsense exist.
- Q (prefix): Grey Hole: An exotic neutron star in which light can get out and matter can get in. It is literally a ginormous Q-ball. Q-balls aren't related to cue balls, in fact, they are any field that has a Noether charge and is stable against turning into usual particles of the field.
- α: White Hole: A region of spacetime in which nothing can enter. They can't exist here, but in a parallel universe, they might.
Life of a Star
Depending on the mass of the star, it's life cycle will be different.
If the mass of the star is less than 0.08 solar masses, which is typically the case for Y, T, and lighter L-type stars, it would be unable to fuse hydrogen, and it would be a brown dwarf which would continue to cool until it emits no light.
If the mass of the star is between 0.08 and 0.45 solar masses, a massive L, or M-type red dwarf, they would slowly burn the hydrogen and will last for trillions of years. The red dwarf would eventually radiate quicker and become hotter, as a result, becoming a "blue" dwarf. Eventually, this blue dwarf would turn into a white dwarf after its hydrogen becomes completely burned out. The white dwarf would turn into a black dwarf after a quadrillion more years.
If the mass of the star is between 0.45 and 8 solar masses, which is the case for K, G, F, and A-type stars, the star would burn hydrogen for a few million to a few billion years, until it becomes exhausted. The star would expand into a red giant and then shed its outer layers. The dust and gases create a planetary nebula and in the center, where the star used to be would be a white dwarf. This white dwarf would eventually turn into a black dwarf after a quadrillion years.
If the mass of the star is between 8 and 15 solar masses, which is the case for B-type stars, the hydrogen supply will be burnt out extremely quickly, within a few million years, and the star will expand into a red supergiant. The supergiant will fuse heavier and heavier elements until it reaches Iron, which cannot be fused. The iron builds up at the core and the balance between gravity and nuclear fusion is broken. Gravity wins, and the star implodes violently, creating a supernova. Elements heavier than Iron and Nickel are created in this supernova, and the remnant is one of two things, depending on the mass of the core before it imploded. If it was greater than 1.4 solar masses, the remnant is a neutron star. If it was greater than 3 solar masses, it becomes a stellar-mass black hole.
Any star from L to B to D to even PS have the capabilities of forming planets. But a star perfect for life-sustaining conditions on the planets must be warm. Not too hot, but not too cold. Sometimes, they are referred as 'Goldilocks' zones. F, G, and K-types are the best at having these. For G-types like our Sun, planets have to be about 1 AU away to be habitable. There's a little table down there showing how far away a planet has to be in order to be habitable. Ones that are bolded are the BEST candidates for habitable planets due to totally not killing us with massive quantities of radiation (which hotter stars are likely to do) or freezing us due to not providing enough light (which colder stars are likely to do). F-type stars have a habitable zone 2 AU away, but they will appear brighter than the Sun, so aliens, be careful, if your star is a F-type. M and L-type stars may have a habitable zone, but the planets may be tidally locked to the star, so the side facing the star may be boiling and the side facing away from the star may be freezing. So the only way for aliens to live is for them to be living on the prime meridian.
However, lots of M-stars have been found to have planets that may be habitable, so tidal locking isn't too much of a problem. T-dwarves and Y-dwarves most likely don't have a habitable zone because they don't emit very much light or heat at all, and if the planet was close enough to be habitable, it would be tidally locked and strong tidal forces will trigger a greenhouse effect, making the planets inhabitable. D and PS types most likely would never have habitable planets, because even at their extreme temperatures, they are extremely dim. So photosynthesis may not exist on those planets, so no aliens. O-types may have a habitable zone extending around 300 AU. However, those types produce so much UV radiation that it may blast the precious atmosphere away, even at those insane distances. So there would be no way for life to breathe and they would have really, really serious cancer. And life doesn't want that. So, we are lucky that the Sun is not an O-type star.
|Class||Average Distance for planet
|O V||316.23 AU|
|B V||31.62 AU|
|A V||4.47 AU|
|F V||2 AU|
|G V||1 AU|
|K V||0.44 AU|
|M V||0.1 AU|
|L V||0.01 AU|