STELLAR CLASSIFICATION

Twinkle, twinkle, little star, how I wonder what your Hertzsprung-

Russell diagram classification….are.

Kinds of Stars

Stars are generally grouped into three colors: red, yellow, and blue, from coolest to hottest.

Technically, they are classified by temperature, but color is a side-effect of that.

Scientists classify them with letters: O,B,A,F,G,K,M. O,B, and A are blue, F is bluish-yellow, G and K are yellow, and M is red.

Size

As you can see, hotter, bluer stars are MUCH larger than smaller, cooler stars, such as our Sun, which is a G-type star.

You would be bacon if the Sun were an O-type star.

Yellow Stars

The Sun, like about 1/5 of the stars in the universe, is a middle-of-the-line, pleasant yellow star.

Yellow stars (types G and K )are generally around 3,700–6,000 K hot, and can range from .7 to 1.15 times as big around as the Sun.

Mr. Sun, Sun, Mr. Golden Sun…..

Red Stars Red stars (type M) make up

the vast majority of stars in the universe—nearly ¾.

They tend to burn at less than 3,000 K, are generally less than half as massive as the sun, and last the longest of any star type.

If the Sun were a class-M star, you would be a popsicle.

What about weird red stars??????????????

Blue Stars Blue stars are the hottest, shortest-lived, and

biggest stars on the Main Sequence (more on that later).

They can burn at anything from 6,000 K to well over 30,000 K, can be from 1.04 times as massive as the sun to over 16 times as massive, and can be as much as 6.6 times as big as the sun.

You would be, not just bacon, but extra-crispy, charred, ugly bacon if this were the Sun.

What about weird blue stars????????????????????

Weird Red Stars

Red dwarfs are small, very cool

stars. Most stars in the universe are

red dwarfs.

Red giants and supergiants are cool, gargantuan stars late in life. The Sun will probably become a red giant in a few billion years, swelling up so big it swallows Mercury and Venus. Earth will likely become a ball of molten rock! (Hope your great-great-great grandkids have sunscreen.)

Enough strangeness! Back to regular red stars!

Weird Blue (or white) StarsWhite dwarfs are small, cool, but very heavy stars. The Sun, after swelling up into a red giant, will probably collapse and become a white dwarf. They can be as heavy as the Sun, but as small as the Earth.

Blue giants (and supergiants) are the hottest, brightest, and heaviest stars in space, though red supergiants can be bigger. They’re short-lived, and very rare, but they’re so bright that we can see quite a few from Earth.

On the left, a blue giant. On the right, a strangely reddish B-type star. In the middle, the good old Sun.

This is weird, man! Get back to the regular stuff!

EXPLOSION!!!!!!!!!!!

When a large star meets certain conditions, it can explode violently in an event called a nova, or in bigger cases, a supernova. The Sun is to small to “go nova,” but we have witnessed many such explosions from Earth. The elements ejected in a supernova may eventually collapse and form a new star. Also, most scientists are pretty sure that the heavier elements in the universe (everything except hydrogen, really) was originally formed in the nuclear furnace of a supernova. So, the carbon in your body was probably once in the heart of a behemoth star!

The Stellar Retirement Home

Small- to medium-sized stars tend to become red giants, then white dwarfs late in life, before cooling into a so-called brown dwarf that’s halfway between a planet and a star. Larger stars, however, have more fun in their senior years.

A neutron star is what you get when a large star goes supernova, then collapses afterwards. They can be as little as 12 kilometers around, but heavier than the sun, giving them a mass of 370 quadrillion (370,000,000,000,000,000) kilograms per cubic meter.

A black hole is often the result of a truly gargantuan supergiant collapsing, though scientists think there are other ways to create one. Black holes are so dense, not even light can escape from them, so the only way to see one is by the distortion of things behind it. Despite their names, they are not “holes,” but rather, probably spheres.

Hertzsprung-Russell Diagram

The HR-Diagram, as it’s known for short, is a graph used to organize stars by two of their characteristics. Surface temperature (usually in Kelvin) is plotted on the X-axis, while luminosity (how bright the star is, measured in multiples of the Sun’s brightness) forms the Y-axis. The so-called Main Sequence forms a rough line down the middle of the diagram, with hotter, brighter blue stars at the top left and cooler, dimmer red stars at the bottom right. White dwarfs, which are dim but very hot, form an island on the bottom left, while supergiants, which are bright but vary in temperature, hover around the top right.

Any Questions?

All images courtesy of www.wikipedia.com and posted here and there in accordance with free use policies.