Ch. 9 The Lives of Stars from Birth through Middle Age

The Cone Nebula

Milky Way Photo, showing dark clouds and nebula

Interstellar matter

• Gas and dust

• Dust grains about 10-7 m in diameter, about the size of smoke particles

• Dust causes reddening of the light that passes through it, but NOT redshift.

• This is due to absorption of the blue components of light (more-so in UV).

Light Reddening due to absorption by dust.

Light from a star has some absorption lines due to the chromosphere.

Additional light reddening is due to absorption by dust.

Interstellar gas

• The interstellar gas is very dilute, about ONE atom per cubic centimeter.

• In some places it is much denser.

• The distribution of gas is very uneven.

• It is mostly Hydrogen (90%), Helium (9%), and everything else (1%).

Detail of Trifid nebula, showing a pillar of cold molecular gas, &a jet coming out of a hidden star, which is about 0.5 parsec long.

Expand this some.

detail of

EGGs:

EvaporatingGaseous Globules

these can be seen as pillars and egg-like objects

Some properties of these nebulae: note that these are AVERAGE quantities; the nebulae are actual quite uneven in their density and temperature. Note the huge masses and sizes.

Figure 11.9Emission Nebula Spectrum

Radio Emission reveals the dark dust cloud.

Horsehead Nebula (neck is about 0.25 pc across)

A reflection nebula is seen

to the lower left of the horsehead.

Horsehead Nebula

(The neck is about 0.25 pc across)

A nice example

of a dark dust

cloud

Hydrogen 21-cm Emission (shortwave radio)

Molecules near M20, visible photo with contour plot of 21 cm radio intensity

This cold dark cloud is probably in stage 1 of star formation

Molecular Cloud Complexes in outer portion of the Milky Way galaxy,

looking away from the center.

This is a false-color image which corresponds to the intensity of the emission from CO gas. The density in these molecular clouds can be a million times the average, or about one million molecules per cubic centimeter.

Star formation – a 7 stage process

• 1 – an interstellar cloud• 2 – shrinking cloud fragments • 3 – a fragment is the size of our solar system• 4 – protostar center reaches 1,000,000 K • 5 – protostar at ~10 solar radius, 4000K surf. • 6 – ignition of fusion in core, now a star• 7 – reaches main sequence

Orion Nebula, Up Close

Orion Nebula, A closer look

reveals “knots” or EGGs, some of which may

contain protostars.

Several disks that may be protoplanetary disks are found after blowing up the Hubble photo.

A protostar can be plotted on the H–R

diagram after reaching stage 4.

It is heated solely due to contraction and is fairly cool, but might be 1000 times as luminous as our Sun, mostly in the infrared part of the spectrum.

Interstellar Cloud Evolution toward a protostar.

Stages of evolution of a star like the Sun

Newborn Star on the H–R Diagram

Stage 5 – T Tauri stage – has violent surface activity and

may form “jets”

Stage 6 – core at 10 million K and finally get fusion

Stage 7 – reaches the main sequence

Prestellar Evolutionary Tracks

for stars of other masses

The minimum mass needed to get

nuclear fusion and produce a real star is about 0.08 solar mass, or about 80 times the mass of Jupiter. With less

mass all we get are “brown dwarfs”