Hertzsprung-Russell Diagram and the

From a birth to death

All stars form in +/- the same manner the sun did A nebula collapses (due to its own

gravity) Cloud contracts to form a hot dense

center Friction increases the temp. until it

reaches ignition temp. for nuclear reactions (HHe)

Ta da! A new star.

After birth:

If the star is like our sun: It enters what is called its main sequence. Main sequence lasts approx. 10 billion

years. During the main sequence the star burns

(HHe) and experiences an increase in temperature. (It creates more and more heat as it goes.) It also becomes brighter, or more luminous.

Next it becomes a red giant.

Red Giant

Mira

Red Giants When a star gets to this phase its outside

layers are expanding and cooling as all of the the H has been turned into He.

There is a hard shell of H just outside the He core. This creates a great heat that is spread out across the expanded surface area.

Thus, the luminosity becomes brighter while the temperature becomes lower.

This results in the red color of red giants. Note: this is a short phase – 100,000,000

m.y.

White Dwarf Stars The sun sized star then enters the final

stage of its life: Very Dense! About a ton of matter in the

size of a table grape. Energy production ends as He becomes

Carbon The outer layers are shed Results in a planetary nebula

The core of the PN holds a small, hot, earth sized star – the white dwarf.

It gradually cools, loses its luminosity and becomes: An undetectable black dwarf – the cinder of a

once active star.

Ancient White Dwarf stars – Milky Way

Sirius A and Sirius B

Massive stars

If the star is massive it is higher on the main sequence. (Hotter, brighter, more massive)

Its lifespan is much shorter b/c it uses up all its fuel quickly.

Called a supergiant. (8-10x bigger than Sun) It makes far more elements: H, He, C, O,

Ne, Mg, Si, Fe, Ni Ends in a supernova explosion.

R136: A Cluster of Massive Stars in Nebula 30 Doradus

Star WR124 detail

Special Note: Black holes Stars about 20x bigger than the Sun

will usually form a black hole. The collapse forms matter that is so

dense nothing, not even light can escape from it.

OVERVIEW

After it’s born…how do we describe it?

There are many kinds of stars. They are classified by: Temperature Luminosity (brightness) Color (spectrum) Size (diameter) Mass (density/cubic area)

It’s all connected…how?

Stars are assigned spectral (visible light arranged according to wavelengths) types These spectral types describe the

temperature and color of the star. They are: O, B, A, F, G, K, M. Numbers

classify them even more specifically. (ex: A5) The colors are (in order, hottest coolest):

Dark blue (O5), light blue (B5), yellow (F5), orange (G5), red (M5)

Eta Car STIS Spectrum

Eta Carinae – star on the brink of destruction

The combinations of:

Temperature Brightness (or luminosity) Color (or spectra)

Describe something called its magnitude.

All of these things interact to express varying levels of energy output.

Used to be classified/organized on something called the: Hertzsprung-Russell diagram.

Hertzsprung-Russell Diagram

Hertzsprung-Russell Diagram