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Different Types of Stars in the Universe

Dr. Thomas Swan is a published physicist who received his PhD in nuclear astrophysics from the University of Surrey.

The globular star cluster, NGC 1466, shows us the diversity of stars. Heavier blue stars are pulled toward the middle of the cluster.

The globular star cluster, NGC 1466, shows us the diversity of stars. Heavier blue stars are pulled toward the middle of the cluster.

Stars are enormous spheres of ignited gas that light the cosmos and seed it with the materials for rocky worlds and living beings. They come in many different types and sizes, from smouldering white dwarfs to blazing red giants.

Stars are often classified according to their spectral type. Although they emit all colors of light, spectral classification considers only the peak of this emission as an indicator of the star's surface temperature. Using this system, blue stars are the hottest and are called O-type. The coolest stars are red and are called M-type. In order of increasing temperature, the spectral classes are M (red), K (orange), G (yellow), F (yellow-white), A (white), B (blue-white), O (blue).

This bland categorization may be abandoned for a more descriptive alternative. As the coolest stars (red) are usually the smallest, they are called red dwarfs. Conversely, the hottest stars are often called blue giants. However, it is also common for stars to become red giants toward the end of their evolutionary cycle.

Many other physical features vary between the different types of star. These include the surface temperature, luminosity (brightness), mass (weight), radius (size), lifetime, prevalence in the cosmos, and point in the stellar evolutionary cycle. The best way to understand these features for other stars is to compare them with the features of our nearest stellar companion, the Sun.

Sun: Physical Characteristics

  • Lifetime: 10 billion years
  • Evolution: middle (4.5 billion years)
  • Luminosity: 3.846 × 1026 W
  • Temperature: 5,500 °C
  • Spectral Type: G (yellow)
  • Radius: 695,500 km
  • Mass: 1.98 × 1030 kg

To understand these solar values, the notation 1026 means the number has 26 zeroes after it. Luminosity is measured in Watts (W) and temperature in celsius (°C).

The types of star identified below will be described in terms of the Sun. For example, a mass of 2 means two solar masses.

The Sun is a yellow dwarf star.

The Sun is a yellow dwarf star.

1. Yellow Dwarf Stars

  • Lifetime: 4 - 17 billion years
  • Evolution: early, middle
  • Temperature: 5,000 - 7,300 °C
  • Spectral Types: G, F
  • Luminosity: 0.6 - 5.0
  • Radius: 0.96 - 1.4
  • Mass: 0.8 - 1.4
  • Prevalence: 10%

The Sun (see above), Alpha Centauri A (one of our nearest neighbors), and Kepler-22 (a star with an Earth-sized exoplanet) are yellow dwarfs. These stellar cauldrons are in the prime of their lives because they are burning hydrogen fuel in their cores. This places them on the "main sequence" of stellar evolution, where the majority of stars are found. The name "yellow dwarf" may be imprecise, as these stars typically have a whiter color. However, they do appear yellow when observed through the Earth's atmosphere.

2. Orange Dwarf Stars

  • Lifetime: 17 - 73 billion years
  • Evolution: early, middle
  • Temperature: 3,500 - 5,000 °C
  • Spectral Types: K
  • Luminosity: 0.08 - 0.6
  • Radius: 0.7 - 0.96
  • Mass: 0.45 - 0.8
  • Prevalence: 11%

Alpha Centauri B and Epsilon Eridani (a nearby star with an exoplanet) are orange dwarf stars. These are smaller, cooler, and live longer than yellow dwarfs like our Sun. Like their larger counterparts, they are main sequence stars fusing hydrogen in their cores.

An orange dwarf called Epsilon Eridani (left) is shown next to our Sun (right) in this illustration.

An orange dwarf called Epsilon Eridani (left) is shown next to our Sun (right) in this illustration.

3. Red Dwarf Stars

  • Lifetime: 73 - 5500 billion years
  • Evolution: early, middle
  • Temperature: 1,800 - 3,500 °C
  • Spectral Types: M
  • Luminosity: 0.0001 - 0.08
  • Radius: 0.12 - 0.7
  • Mass: 0.08 - 0.45
  • Prevalence: 73%
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Proxima Centauri (our nearest neighbor), Barnard's Star (a nearby star) and Gliese 581 (a star with a planetary system) are all red dwarfs. They are the smallest kind of main sequence star. Red dwarfs are barely hot enough to maintain the nuclear fusion reactions required to use their hydrogen fuel. However, they are the most common type of star, owing to their remarkably long lifetime that exceeds the current age of the universe (13.8 billion years). This is due to a slow rate of fusion and an efficient circulation of their hydrogen fuel via convective heat transport.

Binary red dwarf stars. The smaller star, Gliese 623B, is only 8% of the Sun's mass.

Binary red dwarf stars. The smaller star, Gliese 623B, is only 8% of the Sun's mass.

4. Brown Dwarfs

  • Lifetime: unknown (long)
  • Evolution: not evolving
  • Temperature: 0 - 1,800 °C
  • Spectral Types: L, T, Y (after M)
  • Luminosity: ~0.00001
  • Radius: 0.06 - 0.12
  • Mass: 0.01 - 0.08
  • Prevalence: unknown (many)

Brown dwarfs are substellar objects that never accumulated enough material to become stars. They are too small to generate the heat required for hydrogen fusion. Brown dwarfs constitute the midpoint between the smallest red dwarf stars and massive planets like Jupiter. They are about the same size as Jupiter but they must be at least 13 times heavier to qualify as a brown dwarf. Their cold exteriors emit radiation beyond the red region of the spectrum and, to the human observer, they appear magenta rather than brown. As brown dwarfs gradually cool they become difficult to identify and it is unclear how many exist.

Two tiny brown dwarfs in a binary system (CFBDSIR 1458+10) that is 104 light years from Earth.

Two tiny brown dwarfs in a binary system (CFBDSIR 1458+10) that is 104 light years from Earth.

5. Blue Giant Stars

  • Lifetime: 3 - 4,000 million years
  • Evolution: early, middle
  • Temperature: 7,300 - 200,000 °C
  • Spectral Types: O, B, A
  • Luminosity: 5.0 - 9,000,000
  • Radius: 1.4 - 250
  • Mass: 1.4 - 265
  • Prevalence: 0.7%

Blue giants are defined here as large stars with at least a slight blueish coloration, although definitions vary. A broad definition has been chosen because only about 0.7% of stars fall into this category.

Not all blue giants are main sequence stars. The largest and hottest (O-type) burn through the hydrogen in their cores very quickly, which causes their outer layers to expand and their luminosity to increase. Their high temperature means they remain blue for much of this expansion (e.g., Rigel), but eventually they may cool to become a red giant, supergiant, or hypergiant.

Blue supergiants above about 30 solar masses can begin to throw off huge swathes of their outer layers, exposing a super hot and luminous core. These are called Wolf-Rayet stars. These massive stars are more likely to explode in a supernova before they can cool to reach a later evolutionary stage, such as a red supergiant. After a supernova, the stellar remnant becomes a neutron star or a black hole.

A close-up of the blue giant star, Rigel. It is 78 times larger than the Sun and the 7th brightest star in the night sky (i.e., from Earth).

A close-up of the blue giant star, Rigel. It is 78 times larger than the Sun and the 7th brightest star in the night sky (i.e., from Earth).

6. Red Giant Stars

  • Lifetime: 0.1 - 2 billion years
  • Evolution: late
  • Temperature: 3,000 - 5,000 °C
  • Spectral Types: M, K
  • Luminosity: 100 - 1000
  • Radius: 20 - 100
  • Mass: 0.3 - 10
  • Prevalence: 0.4%

Aldebaran and Arcturus are red giants. These stars are in a late evolutionary phase. Red giants would previously have been main sequence stars (such as the Sun) with between 0.3 and 10 solar masses. Smaller stars do not become red giants because, due to convective heat transport, their cores cannot become dense enough to generate the heat needed for expansion. Larger stars become red supergiants or hypergiants (see below).

In red giants, the accumulation of helium (from hydrogen fusion), which is a heavier element than hydrogen, causes a contraction of the core that raises the internal temperature. This triggers hydrogen fusion in the outer layers of the star, causing it to grow in size and luminosity. However, due to it now having a larger surface area, the surface temperature is actually lower (redder). Red giants eventually eject their outer layers, which form a planetary nebula, while the core becomes a white dwarf (see below).

A close-up of the dying red giant star, T Leporis. It is 100 times larger than the Sun.

A close-up of the dying red giant star, T Leporis. It is 100 times larger than the Sun.

7. Red Supergiant Stars

  • Lifetime: 3 - 100 million years
  • Evolution: late
  • Temperature: 3,000 - 5,000 ºC
  • Spectral Types: K, M
  • Luminosity: 1,000 - 800,000
  • Radius: 100 - 2000
  • Mass: 10 - 40
  • Prevalence: 0.0001%

Betelgeuse and Antares are red supergiants. The largest of these types of stars are sometimes called red hypergiants. One of these is 1708 times the size of our Sun (UY Scuti), and is the largest known star in the universe. UY Scuti is about 9,500 light years away from the Earth.

Like red giants, these stars have swelled up due to the contraction of their cores. However, red supergiants typically evolve from blue giants and supergiants with between 10 and 40 solar masses. Higher mass stars shed their layers too quickly, becoming Wolf-Rayet stars, or exploding in supernovae. Red supergiants eventually destroy themselves in a supernova, leaving behind a neutron star or black hole.

Betelgeuse, a red supergiant, is a thousand times larger than the Sun.

Betelgeuse, a red supergiant, is a thousand times larger than the Sun.

8. White Dwarfs

  • Lifetime: 1015- 1025 years
  • Evolution: dead, cooling
  • Temperature: 4,000 - 150,000 ºC
  • Spectral Types: D (degenerate)
  • Luminosity: 0.0001 - 100
  • Radius: 0.008 - 0.2
  • Mass: 0.1 - 1.4
  • Prevalence: 4%

Stars with less than 10 solar masses will eventually shed their outer layers, forming planetary nebulae. However, they will typically leave behind an Earth-sized core of less than 1.4 solar masses. This core will be so dense that the electrons within its volume will be prevented from occupying any smaller region of space (becoming degenerate). This physical law (Pauli's exclusion principle) prevents the stellar remnant from collapsing any further.

The core, or remnant, is called a white dwarf, and examples include Sirius B (a companion of Sirius A, the brightest star in the night sky) and Van Maanen's star. More than 97% of stars are theorized to become white dwarfs. These super hot structures will remain hot for trillions of years before cooling to become black dwarfs.

The tiny companion of Sirius A is a white dwarf called Sirius B (see lower left).

The tiny companion of Sirius A is a white dwarf called Sirius B (see lower left).

9. Black Dwarfs

  • Lifetime: unknown (long)
  • Evolution: dead
  • Temperature: < -270 °C
  • Spectral Types: none
  • Luminosity: infinitesimal
  • Radius: 0.008 - 0.2
  • Mass: 0.1 - 1.4
  • Prevalence: ~0%

Once a star has become a white dwarf, it will slowly cool to become a black dwarf. As the universe is not old enough for a white dwarf to have cooled sufficiently, no black dwarfs are thought to exist at this time.

Artistic impression of how a black dwarf may appear against a backdrop of stars.

Artistic impression of how a black dwarf may appear against a backdrop of stars.

10. Neutron Stars

  • Lifetime: unknown (long)
  • Evolution: dead, cooling
  • Temperature: < 2,000,000 ºC
  • Spectral Types: D (degenerate)
  • Luminosity: ~0.000001
  • Radius: 5 - 15 km
  • Mass: 1.4 - 2.3 (although 1.1 - 1.4 solar masses is possible)
  • Prevalence: 0.7%

When stars larger than about 10 solar masses exhaust their fuel, their cores dramatically collapse to form neutron stars. The collapse throws off the outer layers of the star in a supernova explosion. If the core still has a mass above about 1.4 solar masses, electron degeneracy will be unable to halt the collapse. Instead, the electrons will fuse with protons to produce neutral particles called neutrons, which are compressed until they can no longer occupy a smaller space (i.e., becoming degenerate).

The stellar remnant, composed almost entirely of neutrons, is so dense that it occupies a radius of about 12 km. Due to conservation of angular momentum, neutron stars are often left in a rapidly rotating state called a pulsar.

The Crab pulsar is a neutron star at the heart of the Crab Nebula (the central bright dot).

The Crab pulsar is a neutron star at the heart of the Crab Nebula (the central bright dot).

When Does a Star Become a Black Hole?

Stars larger than 20 solar masses with cores larger than about 2.3 solar masses are likely to become black holes instead of neutron stars. For a black hole to form, the density (and associated pressure) in the core must become great enough to overcome neutron degeneracy, causing a further collapse into a gravitational singularity.

The supermassive black hole at the core of the Messier 87 galaxy.

The supermassive black hole at the core of the Messier 87 galaxy.

While stellar classification is more precisely described in terms of spectral type, this does little to fire the imaginations of those who will become the next generation of astrophysicists. There are many different types of stars in the universe, and it is no surprise that those with the most exotic sounding names receive the greatest levels of attention.

Explore the Cosmos

© 2013 Thomas Swan


Robert A. Jackson on April 24, 2020:

You might have mentioned magnetars,as they are the coolest of neutron stars, which are pretty cool in their own right. Not that I'd want one in MY neighborhood.

me on April 09, 2020:

so helpful

me on April 07, 2020:

so helpful

Ycn_OmAr on March 10, 2020:

Very helpful. Hopefully i get a A on my writing.

raven on December 12, 2019:

thanks 4 the fact

E. R. on November 05, 2019:

This helped me answer my questions for an article that I'm writing :)

Hiba Baydoun on November 04, 2019:

Thank a lot. Because of this I won the science fair competition

Pepe on October 28, 2019:

Cool your presentation is awesome it help me a lot

Prajal Gurung on October 18, 2019:

Thank you for helping in my science project

George on October 07, 2019:

Thanks really helped me do my project work

L on October 03, 2019:

Bio-Large neutron stars (over 40 solar masses) blow up and become black holes-just like it says.

ashton kole scoggins on September 20, 2019:

it help me so much

Dan on August 16, 2019:

Thanks so much I really needed this for my project for highschool, starting in September.

A on July 24, 2019:

Very helpful

Blo on May 13, 2019:

Nothing about stars that blow up and turn into black holes?

You don't know? That's just wrong

edward on May 07, 2019:

good details a lot of information. i needed it for my project

21 SAVAGE Roblox/Fortnite/Call of duty etc on May 05, 2019:

Thx a lot for this info bro

Thomas Swan (author) from New Zealand on May 05, 2019:

It's a yellow dwarf according to this classification.

Dave on April 09, 2019:

You saved me, if this was not created I would have unfinished homework to do during recess

Gary.K on March 15, 2019:

The best text ever. Got me a A+ for my information report! AWSM!!!!

deer on November 29, 2018:

this is really good !!!!!!

Me (A Kid) on November 29, 2018:

This article helped me a lot for my science project

-Youtube channel (PhantomMax9)

Miliyeganegi on November 20, 2018:

These information completely answered all my questions about stars, thanks alot.

hans carlos on November 09, 2018:

very helpful thx bro

Thomas Swan (author) from New Zealand on August 06, 2018:

Hi Vic. To my knowledge, each star in a binary pair conforms with one of the types described here. And, Mercury-Manganese stars simply have an abundance of those elements in their atmospheres, but fit the profile of a blue giant by the (broad) definition given here. They still burn hydrogen and helium.

Vic fedorov on August 03, 2018:

What about binary stars? What about mercury magnesium stars burning other than hydrogen or helium.

Giuseppe on May 25, 2018:

This is really helpful

Love science on May 18, 2018:

this really helped me

Name on May 17, 2018:

Hey that's pretty good,

sucks that I'm color blind

space learner 34 on May 02, 2018:

so much good to learn! i was glad cause i needed it for a project about space

Hacker 52 on April 22, 2018:

really helpful!!!

Rensama3175 on March 18, 2018:

Thank you for this info Dr.Thomas Swan it's a great big help for me and the others

Dj Soundwave on February 05, 2018:

Dr. Swan hit it out of the park with this. I never really thought about why when I heard “if you weight a teaspoon of neutron stat on earth, it would be A LOT”. After this article, I have a picture painted in my head about why. Electron degeneracy is the culprit. Being unable to occupy smaller space. Duh when I say it tho. Great article!!

Yeon Hwa Kim on January 30, 2018:

Wow!!thanks for that very educational info !!!!it is a great help for me!!!

asdf on December 05, 2017:

no blue super giant or blue hyper giant

famma on December 03, 2017:

Thank you soooooo much for all these information, it helped me a lot in my presentation...;)

alyssa morgan haaff on November 28, 2017:

it is cool to learn so much about stars

Anonymous person on October 26, 2017:

Cool facts.

214 on May 16, 2017:

So Cool. Great Info best website for stars! :)

Mikayla on May 04, 2017:

where is the black hole? in math/science class my math teacher said that every star starts as a nebula and if they turn into a high-mass proto star and they either end as a neutron star like you have or a black hole, so could you maybe add the black hole on your spare time


hala at ya home boy on March 13, 2017:

very educational. This website really helps when it comes to learning about stars.

RaelthekidRS_YT on February 24, 2017:

Dude Great presentation and i will always support your presentation!

Robo girl 33 on January 09, 2017:

Perfect info great for kids

MiriamtheGeek on November 20, 2016:

Very good! It helped me a lot. I used this website for extracurricular research

Doug West from Missouri on August 10, 2016:

Reading you Hub makes me want to go out and look at the stars tonight. I haven't taken my telescope outside in a while.

Arun Dev from United Countries of the World on June 29, 2015:

Stars are amazing!

Kristen Howe from Northeast Ohio on January 26, 2015:

Beautiful, Thomas! I love stars, especially if I can see them on a clear night without any obstructions. Very useful and informative knowledge. I always make a wish on them, too, if I can...

Thomas Swan (author) from New Zealand on January 19, 2015:

Glad to be of help allyssa.

allyssa jhane liberato on January 19, 2015:

it helps me for doing my assignments fastly

Thomas Swan (author) from New Zealand on September 23, 2014:

Thanks m abdullah. Glad you liked it.

muhammad abdullah javed on September 23, 2014:

You have nicely dealt with the details of the starts of our known galaxies. Thank you Thomas. Voted interesting up.

Thomas Swan (author) from New Zealand on September 18, 2014:

Thanks Ruby! Sorry I missed your comment before. I've been going through my hubs and finding some of the comments I missed. I'm glad you found it interesting! :)

Maree Michael Martin from Northwest Washington on an Island on January 22, 2014:

Wow, so very cool to learn so much more about stars.

Thomas Swan (author) from New Zealand on January 22, 2014:

Thanks for commenting Alliah. The Sun burns without oxygen because oxygen is only needed for chemical reactions in which bonds between atoms are formed. The Sun burns via nuclear reactions in which nuclear particles (protons and neutrons) and bonded together. The nuclear scale is smaller than the atomic scale (remember, each atom contains a nucleus). The nuclear scale doesn't need oxygen, but it does need very high temperatures and pressures, such as those found in stars.

Alliah on January 11, 2014:

These are the most interesting, thing that I have ever read in my life.

As of today, in the question .How does the sunburn with out oxygen?

But seriously how does the sun burn without any oxygen in the outer space.Can someone tell me about this one I just really want to know,

as if!

Thomas Swan (author) from New Zealand on December 18, 2013:

That's an interesting question. Would like to know why you've asked it before answering. If you've found a copy somewhere on the web, please let me know asap.

hubblehartsu on December 18, 2013:

when was this article published

Thomas Swan (author) from New Zealand on November 13, 2013:

Thanks for commenting lone77star. I suppose one could say that the most interesting planets are around the least interesting stars; so perhaps that is their consolation prize. I agree that in terms of chemical composition, the most interesting stars are the metal-rich, 2nd/3rd generation ones.

Rod Martin Jr from Cebu, Philippines on November 13, 2013:

I've never really been fascinated with the exotic types. I go in for the more ordinary, main sequence -- what I call "mid-dwarfs" (F2V - K2V). Especially, the ancient, metal-rich variety, where habitable planets might be found.

Thomas Swan (author) from New Zealand on April 13, 2013:

Thanks for the kind words Rob! I think my fascination for this topic allowed me to finish because it's seemingly impossible to find all of this information in one place on the web. My astrophysics background helped, but I must have used about 20 different sources, and the whole article took two days to finish! I read science fiction too. In my opinion it's the genre that gives the greatest license for the human imagination to flourish.

Rob Winters on April 12, 2013:

A most interesting and comprehensive hub Thomas. Great layout and presentation too. A stellar hub in every sense :-) Voting up & interesting.

I read a lot of Science Fiction so i was familiar with a lot of the terminology and star types and found the details and breakdown of this subject matter most fascinating and informative.

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