Chapter 14: Contʼd
14.3 How did the Milky Way Galaxy 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 Galaxies
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 Spiral Galaxy 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 Barred Spiral Galaxy
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