an introduction to astronomy files/astro/astro10.pdf · 2019. 1. 27. · astronomy, space science,...

An Introduction to Astronomy

Cairo UniversityFaculty of Physical TherapyGeneral Education Program

By

Dr. Zainab Mohamed AwadAstronomy, Space Science, & Meteorology Department

Faculty of Science - Cairo University

2014 Lec. 10

2

In Lecture 9

Stellar Distribution (H-R diagram)

Binary systems

The formation and evolution of stars

The ISM Life Cycle

Stars – P2

General Education Program An Introduction to Astronomy

3

In Lecture 10

Galactic Morphology

Our Galaxy: the Milky Way

The Local group of Galaxies

Large scale structures (P1)

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Galactic Morphology

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What is a galaxy?- A galaxy is a collection of stars, gas and dust bound

together by their common gravitational pull.

Size range:

104 - 2x105 Ly

Brightness:

109 - 1014 Lsun

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The Triangulum Galaxy (M33) @ 2.9 million Ly awayimage from NASA's Spitzer Space Telescope

Structure & TypesCommon features of galaxies

1- gravity holds the stars together

2- the densest region is in the center (core or bulge)

3- all galaxies have a faint outer region or envelope and

a mysterious dark matter halo

4- some galaxies have spiral arms

General Education Program An Introduction to Astronomy 6HST ultra deep field galaxies

Main components of a galaxy

- Nucleus (core/bulge) - The halo (envelope)

- The dark halo (invisible)

- The disc (with arms – exists ONLY in disc type galaxy)

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General Structure

Structure & Types

Galaxy Colours:

The galaxy different components have various types of

stars.

Young stars (hot stars) in discs give them their blue

colour, while older stars (cool stars) in the bulge/halo let

them appear red.

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Structure & Types

Morphological Types- According to their shapes, galaxies can

be divided into 3 main categories

1- elliptical galaxies

2- disc galaxies

3- irregular galaxies

- These classes are known as

morphological types

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- There are other morphological types of

galaxies such as mergers, but these other

types are not in the scope of this course.

Morphological Types

1- Elliptical 2- Disc Irregular

2.1- Normal spiral

2.2- Barred spiral

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Morphological Types

1- Elliptical 2- Disc Irregular

2.1- Normal spiral

2.2- Barred spiral

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Other Morphological Types

1- Merging galaxies 2- Interacting galaxies

Hubble image of two merging spiral galaxies

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Types & PropertiesHubble Sequence

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Types & PropertiesHubble Sequence

Our Galaxy: the Milky Way

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The Milky Way Galaxy

Our galaxy “the MilkyWay” is an example of adisc galaxy of the barredspiral subclass

The solar system is located in the galactic disc @ 28000 Ly from the galactic centre on the local arm “Orion”.

Barred spiral

Edge-on diagram of the M.W

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The Milky Way Galaxy

In the late 18th Century, long before distances to starswere known, William Herschel tried to estimate thesize and shape of our Galaxy

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The Structure of our GalaxyGeneralStructure

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The Structure of our GalaxyGeneral Structure

General Properties

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General Properties

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General Properties

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Motion

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General properties of the MW regions

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General properties of the MW regions

The arms are:

- Cygnus

- Carina-Sagittarius

- Norma

- Crux-Scutum

- Perseus

Perseus

Orion local Cygnus

Carina-Sagittarius Crux-Scutum

Sun

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The Structure of our Galaxy

The Milky Way GalaxyA simulation of the Galaxy structure

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Measuring the MW

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Measuring the MW

William Herschel tried to estimate the size and shape ofour Galaxy by counting the stars but he did notrecognize that the “voids” are actually dusty regions.

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Measuring the MW

Variable stars within the galaxy gives a good estimationabout the distance within the galaxy up to 25 Mpc.

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Formation of the MW & Spiral Arms

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Formation of the MW

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Theories of formation of spiral arms

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Density wave theory

Density waves move through galaxy compressing

matter as it passes and setting off star formation

like traffic jam formation on highway

Theories of formation of spiral arms

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Density wave theory

Density waves move through galaxy compressing

matter as it passes and setting off star formation

like traffic jam formation on highway

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self-propagating star formation (or Supernovae

chain reaction)

Supernovae send out waves which creates new

stars and subsequent supernovae.

So stars are formed in specific regions that appear

as arms and over time the regions fade as stars

burn out, or drift away

Theories of formation of spiral arms

The Local group of Galaxies

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The Local Group of Galaxies

rich clusters:

containing thousands of galaxies, D ~ 3 Mpc

poor clusters:

hundreds or less galaxies, D ~ 1 Mpc

The local group is classified as “poor cluster” with about 30 galaxy.

A galaxy cluster is a group of many galaxies.

HST; Abell Cluster of Galaxies

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The Local Group of Galaxies

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The Local Group of Galaxies

The Local Group of Galaxies

Local group most famous members:

MW,

Leo I, Leo II,

Sextant dwarf,

Umi dwarf,

Draco dwarf,

LMC, SMC,

Andromeda (M31)

Pinwheel (M33)

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