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)