Chapter 14: Contʼd

14.3 How did the Form?

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 3 Halo: No ionization nebulae, no blue stars ⇒ no star formation (and hence no recycling)

Disk: Ionization nebulae, blue stars ⇒ star formation Milky Wayʼs star formation rate is about 1 MSun/yr.

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 4 Halo Stars: Halo stars 0.02-0.2% heavy elements (O, Fe…), formed first, only old stars then stopped.

Disk Stars: Disk stars formed 2% heavy elements, later, & keep on stars of all ages forming. 4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 5 Our galaxy probably formed from a giant gas cloud

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 6 Halo stars formed first as gravity caused cloud to contract

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 7 Remaining gas settled into spinning disk due to conservation of angular momentum

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 8 Stars continuously form in disk as galaxy grows older

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 9 The collapsing cloud model explains the age, chemical, and orbital differences between halo and disk stars.

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 10 More detailed studies  Halo stars formed in clumps that later merged (“galactic cannibalism”).

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 11 What lies at the Center of our Galaxy

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 12 Galactic center in IR light

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 13 Galactic center in IR light Galactic center in radio

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 14 Galactic center in radio

Strange radio sources in galactic center

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 15 Strange radio sources in Stars at galactic center galactic center

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 16 Stellar Orbits

Use Newtonʼs version of Keplerʼs 3rd law: 6  mass = 3-4 10 MS  In size of solar system

black hole in center of Milky Way Recent evidence from bright X-ray “flare” emission

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 17 End of Chapter 14

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 18 Chapter 15 A Universe of

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 19 What is a galaxy?

• An enormous collection of stars held together by their common gravity.

• Have a wide range of masses: from 100 million stars (dwarf galaxies) to >1 trillion stars (giant galaxies).

• Lower mass galaxies are more common.

• Galaxies have a wide range of ages, stellar populations (the mix of stars in a galaxy), and gas content.

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 20 How far away are other galaxies?

• Light travels at a finite speed = 300,000 km/s. Destination Distance Sun 8 light-minutes Pluto 8 light-hours Nearest star (α Centauri) 4 light-years Center of our galaxy 30,000 light-years

Nearest large galaxy 2.5 million light-years

Nearest cluster of galaxies 50 million light-years

Most distant known galaxy ~12 billion light-years

• The farther away we look in distance, the further back we look in time. 4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 21 Hubble Ultra Deep Field (10 days of exposures) Elliptical Galaxy

Irregular Galaxies 4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 22 Spiral Galaxy

halo

disk bulge

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 NGC 4414 23

NGC 1300 – 110, 000 light years in diameter

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 24 Disk Component: Spheroidal Component Stars of all ages, (halo & bulge): Old stars, & many gas clouds few gas clouds

NGC 4594 (The Sombrero Galaxy) – 82,000 light years across 4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 25 Blue-white color Disk indicates ongoing Component: stars of all ages, star formation many gas clouds (massive stars)

Spheroidal Component: bulge & halo, old stars, few gas clouds Red-yellow color indicates older star population 4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 26 Elliptical Galaxies All spheroidal component, virtually no disk component. Red-yellow color indicates older star population.

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 27 Irregular Galaxies

The Large Magellanic Cloud – 30,000 lys across Blue-white color indicates ongoing star formation

4/20/2009Irregulars are smallHabbal Astro110-01 and much Chs. 14-15 less Lecture massive 32 than spirals 28 Role of Angular Momentum in Galaxy Formation

4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 29 Recap: The 3 main types of galaxies

• Spiral galaxies have prominent disks and spiral arms.

• Elliptical galaxies are rounder and redder than spiral galaxies and contain less cool gas and dust.

• Irregular galaxies are neither disk-like nor rounded in appearance. 4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 30 Hubbleʼs galaxy classification scheme

Spheroid Disk

4/20/2009Dominates Habbal Astro110-01 Chs. 14-15 Lecture 32 Dominates31 Groups of galaxies Spiral Spirals galaxies are often found in groups of galaxies

(up to a few dozen galaxies)

Elliptical

(Edge-on view) Hickson Compact Group 87 4/20/2009 Habbal Astro110-01 Chs. 14-15 Lecture 32 32 Elliptical galaxies are much more common in huge clusters of galaxies

(hundreds to thousands of galaxies)

4/20/2009Central part ofHabbal galaxy Astro110-01 cluster Chs. 14-15 Abell Lecture 1689 32 33