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Galaxies & Star Systems. Astronomy 2. Star Systems. Our solar system only has one star (our sun); however, most are grouped together to groups of two or more – called star systems Star systems with 2 stars are called double stars or binary stars – 3 stars are called triple stars - PowerPoint PPT Presentation
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Galaxies & Star Systems
Astronomy 2
Star Systems
Our solar system only has one star (our sun); however, most are grouped together to groups of two or more – called star systems
Star systems with 2 stars are called double stars or binary stars – 3 stars are called triple stars
Sometimes binary stars cannot be seen from Earth – only one star can be seen
Star Systems
When one star hides another star it is called an eclipsing star
Astronomers know there are actually 2 stars by looking at the effects of gravity
Our solar system is not the only solar system with planets revolving around a star
In 2000, astronomers discovered a solar system about 10.5 light-years away with planets similar to our solar system
Star Systems
Scientists hypothesize that this solar system might contain life
Since this discovery scientists have been sending out radio waves and looking for radio waves from unnatural sources hoping to discover extra-terrestrial life
However, this could take many years because radio waves travel much slower than light waves
Galaxies
Galaxy: A group of millions or billions of stars, gas, and dust held together by gravity
Our sun and all visible stars are members of our galaxy, the Milky Way
Galaxies
There are 3 main categories of galaxiesSpiral galaxiesElliptical galaxiesIrregular galaxies
Our Galaxy
The Milky Way is visible as a band of light crossing the sky during summer and winter
Represents the concentrated light of the billions of stars in our galaxy
At night, we witness the view from within our galaxy
Milky Way Galaxy
A disk of stars that contains 100-200 billion stars
100,000 light years in diameter, about 3000 light years thick
The center of the Milky Way (nuclear bulge), swells to about 10,000 LY thick
Milky Way Diagram
http://zebu.uoregon.edu/~imamura/123/images/mw-schematic.jpg
Milky Way
Infrared Milky Way (COBE)
http://www.astro.psu.edu/users/niel/astro1/slideshows/class21/slides-21.html
The view from within, in IR light
Sun and Galaxy
Sun located about 2/3 distance away from the center (30,000 light years)
The entire Milky Way rotates around its center
Sun orbits the center of the galaxy at 563,000 mph
One galactic revolution takes 220 million years
Sun’s Revolution
http://www.envirotruth.org/images/graphics/suns_path.jpg
Milky Way, a Spiral Galaxy
Spiral galaxy, most are concentrated in a central nucleus
Spiral arms of stars wind outward from the nucleus
M101
Milky Way Map
http://members.nova.org/~sol/chview/milkyway.jpg
Formation of the Milky Way
Milky Way appears to be about 13 billion years old
MW likely represents one of the original galaxies created after the Big Bang
Sun and planets are 4.5 billion years old
Big Bang origin of universe 13.7 bya
Elliptical Galaxies
Elliptical GalaxiesLook like flattened
ballsContains billions of
stars, but little dust and gas
Due to the lack of dust and gas new stars rarely form
Most elliptical galaxies contain only old stars
Irregular galaxies
Irregular galaxiesDoes not have a
regular shapeOne of the closest
neighboring galaxies to the Milky Way is an irregular galaxy
It is about 160,000 light years away
Star Clusters: Open Clusters
A few dozen to thousands of stars loosely bound together by gravity
Found mainly in the galaxy’s disk and spiral arms
More than 1000 have been discovered in the Milky Way
Young stars that recently formed from nebulosity
Jewel Box open cluster (NGC 4755)
Star Clusters: Globular Clusters
Huge, concentrated balls of thousands to millions of stars
Found in galactic halo, a spherical region centered on the nucleus
Contain the oldest known stars
About 150 globular clusters have been discovered
Omega Centauri, globular cluster (NGC 5139)
Cluster Summary
Type Open Cluster Globular Cluster
Stars Dozens to thousands (Population I)
Hundreds to millions (Population II)
Location Within galactic disk
Orbit galaxy in halo
Age Young, thousands to millions of years
Among oldest known stars (billions of years)
Open Clusters
Pleiades—M45M67
Which cluster is oldest? Note the star colors of the main stars in each cluster
Globular Cluster M55
Colors indicate temperatures, red (cool) to blue (hot)
The “turn off” area on the main sequence represents the cluster’s age
Between the Stars
Space between the stars in a galaxy is a vacuum, or empty space
Also termed interstellar medium
Matter between the stars is of gas and dust
Between the Stars
Interstellar matter 99% gas, 1% dust
Gas consists of 75% hydrogen and 25% helium
Interstellar dust similar in size to cigarette smoke
In spiral galaxies, gas and dust is concentrated in the disk and spiral arms
Pillars of Creation (M16)•In this iconic photo from the Hubble Space Telescope, a small portion near the center of M16, the Eagle Nebula, is revealed
•Note the pink, newly formed stars within the nebula
Barnard’s S Nebula
http://www.astropix.com/HTML/D_SUM_S/B72.HTM
A dark nebula represents interstellar dust that blocks the light of stars from behind
Horsehead Nebula
Famous dark nebula (B33) located near the Belt of Orion
Messier Catalog
All of the Messier objects are shown in this montage
M1 starts the upper left, M110 ends the lower right
Other Galaxies
Until 1924, Milky Way was the “universe”
Edwin Hubble proved that galaxies other than our Milky Way exist
Hubble used Cepheid variable stars to measure the distances to galaxies
Hubble also photographed stars in the Andromeda “Nebula”
The universe contains an estimated 100 billion galaxies. Each of these galaxies contains about 100 billion stars
Andromeda Galaxy
Our nearest large neighbor
Similar in size and shape to Milky Way
Andromeda Galaxy is visible to the naked eye as a glowing spot in the constellation of Andromeda
2.3 million light years distant (wave!)
Andromeda Galaxy (M31, M32, M110)
Andromeda Constellation
Locate M31 and M33
Triangulum Galaxy (M33)
M33
The pink glow of emission nebulas can be seen in this photo
Center of Virgo Cluster
Virgo Cluster near M84, M86
M86
Sombrero Galaxy (M104) from HST
Large-Scale Structure of the Universe
http://www.astro.princeton.edu/~cen/PROJECTS/p1/DARKallz0.jpeg
Sheets & Voids:http://heasarc.nasa.gov/docs/cosmic/sheets_voids.html
Galactic Cannibalism
Galaxies can merge together to form larger galaxies
Elliptical galaxies may be the result of multiple galaxy collisions
NGC 2207 (left) and IC 2163 (HST)
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