Download STELLAR CLASSIFICATIONS: TYPE “O” STARS

STELLAR CLASSIFICATIONS: TYPE “O” STARS
Size:
These stars are 6.6 times bigger
across than the sun, but can reach
sizes hundreds of times bigger,
becoming stars known as
hypergiants. These are the biggest
sizes that stars can possibly get.
Surface Temperature:
30,000 K or more. The light
coming from these stars is actually
mostly in ultraviolet and not in
visible light
Mass:
16 times as much mass as the sun
or more. Since these stars are so
much bigger than the sun, this
means their mass is spread out a
little more. In other words, the sun
is more dense than stars like this. This is because the light coming from these stars has so much
pressure that it puffs the star up.
Luminosity:
These stars are extremely bright, shining 30,000 times brighter than the sun or more. While they
mainly shine in ultraviolet, their visible light is still more than the sun makes. It would be hard
to imagine a star this bright being nearby as it would fill the whole sky.
Lifespan:
Being a super gigantic bright star comes at a price. These stars rarely live longer than 10 million
years, and some live only 1 million. “Live fast and die young” is the motto of these stars.
Color:
These stars mainly put out visible light that looks
blue, as can be seen in the picture to the left of Zeta
Orionis.
Percent of All Stars:
Stars this big are very rare, making up only
0.00003% of all the stars in the galaxy. It is
estimated that there are no more than 20,000 “O”
class stars in the Milky Way galaxy. In comparison,
the galaxy has around 100,000,000 stars in total.
STELLAR CLASSIFICATIONS: TYPE “B” STARS
Size:
These stars are 1.8 to 6.6 times bigger across than
the sun.
Surface Temperature:
These stars are hot. Their surfaces range from
10,000 to 30,000 K. Because of this heat, these
stars have no coronas and there are no spicules
in their atmospheres.
Mass:
These stars are much heavier than the sun. Anywhere from 2.1 to 16 times more
massive. When they die, they end in supernovas, blowing off most of their mass
into space.
Luminosity:
These stars are the first of the extremely bright types. They can be only as dim as
25 times brighter than the sun but can reach brightness up to 30,000 times more
luminous than the sun. When a star gets more massive, it starts getting brighter at a
much faster rate.
Lifespan:
“B” class stars don’t have long lives. At worst they die a mere 11 million years
after birth. At best they only live for only 400 million years. These stars don’t live
long enough to form planets or life so we usually don’t look for planets around
stars like this.
Color:
These stars are brightest in ultraviolet,
but through human eyes they appear to
be blue-white. A perfect example of “B”
class stars would be the Pleiades,
pictured to the left.
Percent of All Stars:
These stars are fairly well, constituting
only 0.13% of all the stars in the nearby
stellar neighborhood.
STELLAR CLASSIFICATIONS: TYPE “A” STARS
Size:
These stars are only slightly larger than the sun. They’re 1.4 to
1.8 times bigger across, but are still much hotter and more
massive.
Surface Temperature:
Like their size, these stars are only somewhat hotter than the sun. 7,500 to
10,000 K at their surface.
Mass:
Class “A” stars are only about twice as massive as the sun, but this makes a big
difference. These stars start at 1.4 times more massive than the sun. This is
enough so that when the star dies, its core turns into a neutron star. The most
massive class “A” stars weigh in at 2.1 times that of the sun. This is enough
mass to cause the core to collapse into a black hole.
Luminosity:
While heavy, these stars only shine 5 to 25 times brighter than the sun. This
would make life on earth hard but doesn’t make a big difference in the cosmic
sense.
Lifespan:
Class “A” stars begin to last long enough for life to possibly form. Their lives
range from 400 million to 3 billion years before they explode and die.
Color:
These stars are still extremely bright and appear
white to blue to the naked eye.
Percent of All Stars:
While these stars only make up 0.6% of all
nearby stars, they’re among the most common of
the stars we can see with the naked eye. When
you look up at the stars at night, you’re mostly
seeing class “A” stars. The brightest star in the
night sky, Sirius, is a perfect example of a class
“A” star.
STELLAR CLASSIFICATIONS: TYPE “F” STARS
Size:
“F” class stars are just a hair bigger than the sun. They weigh 1.15
to 1.4 times more than the sun and behave in just about the same
way.
Surface Temperature:
In addition to being nearly the same mass as the sun, “F” class stars are nearly the
same temperature at 6,000 to 7,500 K. Being slightly warmer means these stars
have a good chance at supporting life.
Mass:
These are stars of masses 1.04 times bigger than the sun to 1.4 times bigger than
the sun. This is still small enough that an “F” class star will end in the same way as
the sun; by turning into a white dwarf.
Luminosity:
While only a little bigger, these stars are actually a fair bit brighter than the sun.
They start at 1.5 times brighter and can get up to 5 times brighter. This may not
sound like much, but imagine if a summer day was 5 times brighter or if winter was
5 times hotter!
Lifespan:
The only big difference between “F” class stars and our own is their lifespan. While
the sun will live for 10 billion years these stars only live 3 to 7 billion. If we lived
around an “F” class star, our sun would already be getting close to death!
Color:
These stars appear white to
the naked eye as can be seen
to the left in this image of
the star Canopus.
Percent of All Stars:
These stars are a minority,
making up only 3% of all
stars in the night sky.
STELLAR CLASSIFICATIONS: TYPE “G” STARS
Size:
These are stars like the sun. The mass can be just under the sun’s
at 0.96 times the sun mass up to just over at 1.15 the mass of the sun.
Surface Temperature:
As we studied in class, stars like the sun have surface temperatures ranging
from 5,200 to 6,000 K. Our sun falls right in the middle of this at 5,500 K.
Mass:
0.8 times the mass of the sun to 1.04
times the mass of the sun.
Luminosity:
While similar to the sun, these stars
can be only half as bright as the sun
to 1.5 times as bright as the sun.
Lifespan:
7 to 15 billion years. The sun sits
right in the middle of this with a
lifespan of 10 billion years. Stars like
our own are great candidates for life. After all, life formed here on Earth!
Color:
Like the sun, these stars appear yellowish-white. You can see this below in an
image of Alpha Centauri, the nearest star to our own.
Percent of All Stars:
We live on a bit of a rare star. Only
about 1 in 10 stars are the same type
as our own.
STELLAR CLASSIFICATIONS: TYPE “K” STARS
Size:
“K” class stars are relatively small and cool. Only 0.7 to 0.96 the size
of the sun. Smaller stars have longer lives, but are cooler, so planets around
these stars would have to be closer to the parent star.
Surface Temperature:
Slightly cooler than the sun. These stars have surface temperatures of 3,700 to
5,200 K.
Mass:
These stars can be small, only half the mass of our own sun. These stars are
much more common than our own because of this. Instead of one star like the
sun, you could get 2 stars of the “K” classification.
Luminosity:
Stars only half the mass of the sun are very dim. Only 0.08 times the
brightness of the sun. This would make a huge difference to life on earth if the
sun only gave 8% as much light.
Lifespan:
These stars are of particular interest in the search for extraterrestrial life
because they are stable on the main sequence for a very long time (15 to 30
billion years, compared to 10 billion for the sun). This may create an
opportunity for life to evolve on terrestrial planets orbiting such stars.
Color:
These stars don’t appear to burn
white or blue. Instead they burn
yellow-orange as pictured with
Arcturus below.
Percent of All Stars:
Stars of this type are quite
common. They make up 12% of
all stars.
STELLAR CLASSIFICATIONS: TYPE “M” STARS
Size:
Any star smaller than 0.7 times the size of the sun is classified as an
“M” class star. Stars can get as small as only 7.5% the size of the sun. This is
only about 10 times bigger than the planet Jupiter.
Surface Temperature:
Less than 3,700 K. These stars are the equivalent of barely-warm embers.
Mass:
Anything less than about half the mass of the sun gives an “M” class star.
These masses can go all the way down to just 10 times the mass of Jupiter,
which is about the minimum mass needed for nuclear fusion.
Luminosity:
These stars are dim. Less than 0.08 times as bright as the sun. Red dwarfs emit
most of their radiation as infrared light so anyone living on a planet around
one of these stars would have to live close and be able to see heat.
Lifespan:
The one biggest plus to “M” class stars is that they live a very long time. 56
billion years on average. With lifespans more than 5 times that of the sun,
there’s plenty of time for life to evolve around a star such as this.
Color:
These stars appear orange-red in the visible spectrum, but emit most of their
light in the infrared. Even in the infrared, though, they’re still quite dim.
Barnard’s star is shown in the picture to the side and the only reason it appears
bright is because its very close.
Percent of All Stars:
“M” class stars make up most of all
the stars in the sky at 76.45%. This is
good news as it means stars will be
around for a long time!
STELLAR CLASSIFICATIONS: TYPES “L” and “T”
Stellar objects with these classifications are not technically stars, but are still
worth knowing. These are “sub-stellar” objects, commonly called red and
brown dwarfs. What distinguishes these objects from real stars is that dwarfs
do not undergo stellar fusion. Their cores never quite reach a high enough
temperature to turn hydrogen into helium. So why do we not just call them
planets and be done with it? Because they’re still large enough to glow from
all the heat generated when they formed. Think of them like super-large gas
giants that glow.
Type “L” Dwarfs:
Also called “red dwarfs”, these dwarfs have a temperature between 1,300 K
and 2,000 K. Some of the hottest ones just barely undergo nuclear fusion and
are classified as stars. The rest do not and are definitely dwarfs. Their
blackbody peak is at the border between red and infrared, so they appear only
dimly red.
Type “T” Dwarfs:
These are sometimes called “brown dwarfs”. They’re even cooler than red
dwarfs, with temperatures between 700 K and 1,300 K. For scale, remember
that Venus has a surface temperature of about 730 K! At this point, what
we’re looking at is more a large planet than a star.
STELLAR CLASSIFICATIONS: TYPE “D”
As stars die, they start to act pretty weird, so we give them a few special
classifications. While also not technically stars, these are also worth knowing
as we see them quite a bit. Class “D” stars are what are known as
“degenerate” stars. This is just a fancy way of saying “dead”. After a star dies,
it blows off most of its layers, leaving just the core behind. This core is
usually made of one of the elements from carbon to iron and is very bright and
hot. Most of them are about the size of Earth.
As time goes on, the dead core of the star slowly cools, getting dimmer as it
goes. This is the final fate of many less massive stars.