Transcript Stellar Classification

Twinkle, twinkle, little star, how I
wonder what your HertzsprungRussell diagram classification….are.
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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.
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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.
Mr. Sun, Sun, Mr.
Golden Sun…..
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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.
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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??????????????
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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 extracrispy, charred, ugly bacon if this were the
Sun.
What about weird blue
stars????????????????????
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.)
Red dwarfs are
small, very cool
stars. Most stars in
the universe are red
dwarfs.
Enough strangeness! Back to
regular red stars!
White 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.
This is weird, man! Get back to the
regular stuff!
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.
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!
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.
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.
All images courtesy of www.wikipedia.com and posted here and there in
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