What do the Roman numerals mean and how do

stars die

What is luminosity?

• Luminosity is the energy emitted from a star, or basically how bright it is compared to our Sun

• The higher the luminosity, the higher the absolute magnitude (brightness) a star is

• -8.1 star is more luminous than an 8.1 star

OBAFGKM

• O are the hottest stars and are blue

• M are the coolest stars blue

But this doesn’t tell us which star is bigger.

You can have two O class stars, but how do you tell which one is biggest?

What else can help us?

• Next to the spectral class (OBAFGKM), there is a roman numeral.

ROMAN NUMERALS

I II III IV V

I-class stars

• Roman numeral (I) class stars are the biggest and are called supergiants

• Examples: Betelgeuse, Deneb, Eta Carinae, Rigel, Anatares, VY Canis Majoris (largest star ever recorded)

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Where are they located?

III-class stars

• Roman numeral (III) class stars are smaller than supergiants, therefore they are called giants

• Examples: Arcturus, Mira, Aldebaran, Pollux, Polaris

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Where are they located?

V-class stars

• Roman numeral (V) class stars are smaller than giants and are called main sequence stars

• 85-90 percent of all stars lie here

• Examples: Spica, Proxima Centauri, Sun, Procyon, Altair, Achenar, Bellatrix, Vega, Sirius, Regulus, Shaula

. .

Where are they located?

Check for understanding

• What are I-class stars called?

• What are III-class stars called?

• What are V-class stars called?

How stars are born

1.) There’s a big cloud of gas and dust that accretes together.

2.) Temperature and pressure increase in order to support hydrogen fusion

3.) A star is born and burns either fast or slowly depending on size, temperature, luminosity

All stars die but in different ways

• A star’s death is dependent mainly on it’s mass (how much matter there is)

• The more mass you have, the larger you are

• 10Msun = 10 times the mass of the Sun

• 100Msun = 100 times mass of the Sun

• .5Msun = ½ the mass of the Sun

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What keeps the star alive?

• Nuclear fusion keeps the star in stellar equilibrium

• The pressure pushing down is equaled by the energy pushing out from the core of the star

• Once the fusion stops, the star starts to collapse inward due the overlying pressure

How low mass stars die

• Stars with less than 10 solar masses generally die a pretty boring death.

• Such stars include most of the entire main sequence (V-class stars)

After the collapse…

• Once the star runs out of fuel it collapses in, but the heat and pressure increase rapidly which jumpstarts the fusion again

• The star continues to expand it’s outer helium later getting bigger and bigger creating a red giant

• Giant = bigger so luminosity does….?

.

Red Giant

What happens next?

• The temperature can’t increase anymore to fuse the Carbon contained in the core

• The core is very small (size of earth), and doesn’t have a huge grip on the outer layers

• The outer layers then get shed off into space by solar winds

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Planetary nebula

• Planetary nebula is a cloud of ejected space dust from the death of a red giant

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At the center of the nebula

• At the center of the nebula is a white dwarf

• White meaning it is hot, dwarf meaning small

• Cooling core of carbon is left over

Cool for millions/trillions of years

Check for understanding

• Put the events in order for death of a low mass star:

1.) Star collapses

2.) White dwarf

3.) Low mass star

4.) Red Giant

5.) Planetary nebula

6.) Star expands due to increased temperature

7.) Hydrogen fusion stops

How high mass stars die

• Basically everything’s the same as a normal main sequence star until the red giant stage

• Generally a higher mass means a bigger size

• If a star is bigger, it burns at a higher luminosity which increases the energy it emits

Red/Blue Supergiant

• The outward expansion becomes too much for the star because it can’t fuse anymore

• It starts the collapse, but heat and pressure jumpstart fusion again!

• The star then expands to an insane size almost 700 times the size of the Sun

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Red/Blue Supergiant

What’s different?

• During the red giant stage a star can’t fuse Carbon, but a supergiant can because temperatures are higher than 600 million Kelvin

• Carbon fuses into Nitrogen, Oxygen, Sodium, Magnesium, all the way up to Iron, but that’s it.

What happens next?

• The supergiant can’t fuse iron, therefore fusion stops abruptly causing the star to collapse inward very rapidly

Electrons and protons

• Electrons are pressured so close together but they can’t touch, therefore the combine with protons to form neutrons

• The pressure pushing outwards ceases to exist and gravity takes over, incredibly fast

• The star shrinks down to the size of a few kilometers composed entirely of neutrons .

(1) Supernova

• The gravitational collapse releases more 100 times more energy in one second as the Sun does in it’s entire lifetime!

• The layers of gas are shot outwards as a supernova

• Hundreds of billions of degrees!

SUPERNOVA

Stars that could go supernova?

• Betelgeuse

• Antares

• Spica

• Eta Carinae

• VY Canis Majoris

Are supernova’s necessary?

• When a star explodes it releases so much heat that heavier elements after iron can fuse into new elements

• Thus any element after 26 on the periodic table was conceived in the explosion of a supernova!

No planets! No people! No YOU!

Neutron Stars

• After the star explodes, all that is left is a ball of neutrons which weighs A LOT

• One teaspoon of a neutron star weighs as much as Mount Everest!!!

• Rotating neutron stars are called pulsars which radiate high forms of radiation

(2) Black hole

• If the pressure is high enough, the neutron star continues to collapse further into a black hole

• Gravity is so intense that light can’t even escape

• If you pass the event horizon, you will not return

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What happens in a black hole?

• In a black hole you can’t escape

• Your body is stretched out and squeezed into a process called spaghettification!

• You will look like a squeezed out tube of toothpaste

• http://www.youtube.com/watch?v=-K_8R03jIZI&feature=related

Check for understanding

1.) Neutron Star 2.) High mass star 3.) Black hole 4.) Red Supergiant 5.) Supernova 6.) Red Giant

• http://www.youtube.com/watch?v=mzE7VZMT1z8&feature=related –

• http://www.youtube.com/watch?v=Aji_1XwH2CA&feature=related

• http://www.youtube.com/watch?v=qtUMR-uYRZI&feature=related

• http://www.youtube.com/watch?v=ocOhW8PpKj4&feature=related