Chapter 9: Where do Come From? The Lives of Stars Some stars are old, but others are very young; they must have just formed.

What could these stars form out of? Empty Space?

Space is Not _____ How do we know it’s there?

1. ______

2. ______

3. ______The The Orion

This material between the stars is called the ______It is very diffuse and thin…. In fact it is almost a vacuum.

The Interstellar Medium (ISM) The ISM is Visible as _____ Called Nebulae The Interstellar Medium is composed of: !Gas (99%) and Dust (1%) by mass • ______(~75%) • ______(~25%) • ______(< 1%)

The Eagle Nebula Close Up (ground based photo) (Hubble Space Telescope)

1 Emission Nebulae (HII Regions) Three Kinds of Nebulae HII = Ionized Hydrogen

Hot shines on a gas cloud, 1) ______Nebulae ______the gas 2) ______Nebulae Electrons jump to _____ energy levels 3) _____ Nebulae When they fall back to ground state they produce ______lines.

The Fox Fur Nebula The Cat’s Eye Nebula

Reflection Nebulae Blue Reflection Nebulae and the Blue Sky

When a cooler star illuminates a cloud of gas and dust, star light is ______by the dust ______wavelengths A reflection nebulae always appears _____ (blue light) are scattered more Reflection easily than Nebula near ____ The Pleiades wavelengths (red light) by small particles

Close Up

The Trifid Dark Nebulae Nebula • Reflection (blue) -> _____ star Dense clouds of gas and dust can _____ the light • Emission (red) - from the stars > ______star behind them. Barnard 86

Horsehead Nebula

2 Where did the stars go? Interstellar Reddening • Interstellar Dust is in the way!

• Solid particles ____ Dust blocks light coming from (shorter-!) ____ stars light better than (longer- !) ____ • Stars near edges light appear red because of ______

Interstellar Reddening Observing ______Stars

Observations of Visible light from a ______light newborn star is reveal stars on the trapped in the gas other side of the clouds cloud

Observing Newborn Stars

Observing the cloud in IR light can reveal the newborn star

3 Cloud Collapse How do stars form? How does a thin cold cloud of gas and dust become a • One of the 3 dense hot shining star? “origins” questions The problem is ______: • 2 Methods: ISM: 103 atoms/cm3 – Collapse caused by Star: 1023 atoms/cm3 ! ______– Collapse caused by To become a star, the cloud ______must ______tremendously

A star-forming nebula

Gravity versus Pressure Star Formation • Gravity can create stars only if it can overcome the force of ______in a 1. Start with a cloud - ISM cloud 2. Form little _____ regions a. From collapse b. From shock waves 3. Dense regions collapse under ______4. Dense regions get ______

Fragmentation of a Cloud Fragmentation of a Cloud • This simulation • Gravity can overcome pressure in small begins with a pieces of the cloud turbulent cloud containing 50 solar masses of • Gravity becomes stronger as the gas gas becomes ______

• Gas becomes denser, core becomes ______

Fusion!

4 Fragmentation of a Cloud Fragmentation of a Cloud • The random • Each lump of the motions of cloud in which different sections gravity can of the cloud cause overcome it to become pressure can go ______on to become a star

• A large cloud can make a whole ______of stars

Star Formation from Shocks Isolated Star Formation

• Gravity can When a high mass O type star overcome ends its life, it explodes as a pressure in a relatively small cloud if the cloud is unusually dense Material from the exploding star might collide with a nebula in its path…. • Such a cloud may make only a single star : A Supernova which exploded in 1054 AD

Shocks Triggering Star Protostars Formation

Henize 206 Henize 206 Part of a nebula (infrared) Shock waves can (infrared) condenses into a “push” material together in a cloud, knot of gas called creating _____ a protostar. ______Protostars are surrounded by material which Proto-Planetary System can form ______. in The .

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