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Stars and Galaxies
Created by the
Lunar and Planetary Institute
For Educational Use Only
LPI is not responsible for the ways
in which this powerpoint may be used or altered.
February 20, 2009
Image at http://hubblesite.org/newscenter/archive/releases/galaxy/spiral/2009/07/image/g/results/50/
Different
types of
stars
Image from
http://hubblesite.org/newscenter/archive/releases/star%20cluster/globular/2003/21/image/a/results/50/
Types of Stars
Range in size from dwarf to supergiants
Common Colors (based on temp): Red,
Blue, Yellow
Can occur in groups or alone
What is a “star cluster”?
stars formed together at
same time
stars may be
gravitationally bound
together
two types: open
(galactic) and globular
Image at
http://hubblesite.org/newscenter/archive/releases/star%20cluster/globular/2007/18/image/a/format/web/results/50/
Open Clusters
dozens to thousands of stars
young stars! only a few
million years old
may still be surrounded by
nebula from which they formed
located in the spiral arms of a
galaxy
example: Pleiades
Image at http://hubblesite.org/newscenter/archive/releases/star%20cluster/open/2004/20/image/a/results/50/
Open star clusters
Image from http://hubblesite.org/newscenter/archive/releases/star%20cluster/open/2006/17/image/a/results/50/
Globular Clusters
 millions to hundreds of millions of
stars
 old! 6 to 13 billion years
 mostly red giants and dwarfs
 stars are clumped closely together,
especially near the center of the
cluster (densely)
 surround our disk as a halo
Image at
http://hubblesite.org/newscenter/archive/releases/star%20cluster/globular/1999/26/image/a/results/50/
What is a “nebula”?
A cloud in space
Made of gas and dust
Can have stars inside
Most of the ones we see are
inside Milky Way Galaxy
Different types
Orion image at http://hubblesite.org/newscenter/archive/releases/2006/01/image/a/results/50/
1. Large, massive, bright nebulae
Emission
Nebula
•The hot gas is
emitting light
Orion image at http://hubblesite.org/newscenter/archive/releases/2006/01/image/a/results/50/
2. Colder, darker nebulae
Dark dust
blocking the
hot gas
behind it
NOAO/AURA/NSF Image from
http://hubblesite.org/newscenter/archive/releases/nebula/dark/2001/12/image/c/results/50/
3. Leftovers from an Explosion
Supernova
remnant
(smaller, less
gas)
Image at http://hubblesite.org/newscenter/archive/releases/nebula/supernova-remnant/2005/37/results/50/
What is a “galaxy”?
A large group of stars made of billions to
trillions of stars
Also may have gas and dust
Spiral, or elliptical, or irregular shaped
Image at http://hubblesite.org/newscenter/archive/releases/galaxy/spiral/2007/41/results/50/
Spiral galaxy--Andromeda
NOAO/AURA/NSF Images at http://www.noao.edu/image_gallery/html/im0606.html and
http://www.noao.edu/image_gallery/html/im0685.html
Elliptical Galaxies
Images at http://hubblesite.org/newscenter/archive/releases/galaxy/elliptical/2007/08/image/a/format/large_web/results/50/
and http://hubblesite.org/newscenter/archive/releases/galaxy/elliptical/1995/07/results/50/
Irregular Galaxies
NASA and NOAO/AURA/NSF Images at
http://hubblesite.org/newscenter/archive/releases/galaxy/irregular/2005/09/results/50/ ,
http://www.noao.edu/image_gallery/html/im0560.html , and http://www.noao.edu/image_gallery/html/im0993.html
Our Galaxy: the Milky Way
has about 200 billion stars, and lots of gas
and dust
is a barred-spiral (we think)
about 100,000 light-years wide
our Sun is halfway to the edge, revolving at
half a million miles per hour around the
center of the Galaxy
takes our Solar System about 200 million
years to revolve once around our galaxy
The Milky Way
Image at http://news.nationalgeographic.com/news/bigphotos/1945371.html
Mapping the Milky Way
How do we know what our Galaxy
looks like?
We can see stars
 star clusters
nebulae
Galaxies
Measuring Distances
Parallax
As Earth orbits the Sun, we see nearby
stars move relative to more distant
stars
Measuring Distances
What is a Light Year?
It is the distance light travels in
a year.
Light moves at a velocity of
about 300,000 km/s
About 10 trillion km (or about 6
trillion miles) in 1 year.
Radiation
There are lots of types of light (radiation),
including visible and invisible
Electromagnetic spectrum
http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/what_is_ir.html
.
There are different types of spectra
1. Continuous
2. Emission or Bright Line (from
ionized gas, like a nebula or a neon
sign)
3. Absorption or dark line (from stars)
Illustration at http://imagine.gsfc.nasa.gov/docs/science/how_l1/spectra.html
Radiation
All stars emit radiation
Radio, infrared, visible, ultraviolet, x-ray and
even some gamma rays
Most sunlight is yellow-green visible light or
close to it
The Sun at X-ray wavelengths
Image at
http://imagine.gsfc.nasa.gov/docs/sc
ience/know_l1/sun.html
Image and info at
http://imagine.gsfc.nasa.gov/docs/teachers/gammaraybursts/imagine/page18.html
Using a Star’s Spectrum
We can use a star’s spectrum to classify it.
NOAO/AURA/NSF image at http://antwrp.gsfc.nasa.gov/apod/ap010530.html
Stellar Evolution
Hertzsprung-Russell Diagram
Images from
http://www.nasa.gov/centers/goddard/news/topstory/2007/spectrum_plants.html and
http://sunearthday.gsfc.nasa.gov/2009/TTT/65_surfacetemp.php
Young
stars
form in
nebulae
from Small
Magellanic
Cloud
Image at
http://hubblesite.org/newscenter/archive/releases/2007/04/image/a/results/50/
Star-forming region in the Large Magellanic Cloud:
http://hubblesite.org/newscenter/archive/releases/2008/31/image/a/results/50/
Orion image at http://hubblesite.org/newscenter/archive/releases/2006/01/image/a/results/50/
Interstellar “eggs”
Movie at http://www.stsci.edu/EPA/PR/95/44/M16.mpg
Our Sun is a Regular Star
On the “Main
Sequence”
Image at http://www.gsfc.nasa.gov/topstory/20011210insidesun.html
In a few Billion years… Red
Giant
Image at http://hubblesite.org/newscenter/archive/releases/1997/26/image/a/
Our Sun’s Habitable Zone
Billions of years ago, things may have
been different
The Sun was cooler (by up to 30%!)
Earth’s atmosphere was different
(thicker, carbon dioxide)
Animation at
http://www.nasa.
gov/97994main
_BHabitableZon
Conditions will be different in the future e.MPG
By many accounts, increases in the
Sun’s temperature will make Earth
uninhabitable in 1 billion years or
less
By 5 billion years… White
Dwarf
Small, but
very hot
Image at http://hubblesite.org/newscenter/archive/releases/nebula/planetary/1998/39/results/50/
Image at
http://hubblesite.org/newscenter/archive/releases/nebula/planetary/2000/28/image/a/format/web_print/results/50/
Image at http://hubblesite.org/newscenter/archive/releases/nebula/planetary/2004/27/image/a/format/large_web/results/50/
Massive
Stars are
different
On the “Main
Sequence” but
not for long
Image from
http://hubblesite.org/newscenter/archive/releases/nebula/emission/1997/33/results/50/
Betelgeuse—Red Supergiant
Image from http://hubblesite.org/newscenter/archive/releases/star/massive%20star/1996/04/image/a/results/50/
Supernova—Massive Star
Explodes
Images at
http://hubblesite.org/newscenter/archive/releases/star/supernova/2004/09/results/50/
http://hubblesite.org/newscenter/archive/releases/nebula/supernova-remnant/2005/37/results/50/
http://chandra.harvard.edu/photo/2009/casa/
Neutron Star or Pulsar
Image at http://hubblesite.org/newscenter/archive/releases/nebula/supernova-remnant/2002/24/results/50/
Black Hole
Image at http://hubblesite.org/newscenter/archive/releases/2002/30/image/a/results/50/
Neutron Star: the collapsed core of a large
star (10-29 solar masses)- smallest and
densest stars know
Pulsar: “lighthouses” of the universerotating neutron stars that emit a focused
beam of electromagnetic energy
Classifying Galaxies
Galaxies
come in different sizes (dwarf, large, giant)
come in different shapes and classifications
Spirals
Ellipticals
Lenticulars
Irregulars
are fairly close together, relative to their
sizes
Spiral Galaxies
have flat disk, spiral arms, central bulge, and a
surrounding halo
some have a “barred” bulge
are fairly large (no dwarf spirals)
have lots of gas and dust and younger stars in their
arms, but older stars and little gas or dust in their
halos and central bulges
Galaxies
Image at http://hubblesite.org/newscenter/archive/releases/galaxy/spiral/2005/01/results/50/
Spiral galaxy--Andromeda
NOAO/AURA/NSF Images at http://www.noao.edu/image_gallery/html/im0606.html and
http://www.noao.edu/image_gallery/html/im0685.html
Spiral
Galaxy
on
Edge
Image at http://hubblesite.org/newscenter/archive/releases/galaxy/spiral/2006/24/image/a/results/50/
Image at http://hubblesite.org/newscenter/archive/releases/galaxy/spiral/2007/41/results/50/
Elliptical galaxies
range from spherical to football shaped
range from very small to giant
have very little gas or dust
mostly old stars
similar to the central bulge of a spiral galaxy
Elliptical Galaxies
Images at http://hubblesite.org/newscenter/archive/releases/galaxy/elliptical/2007/08/image/a/format/large_web/results/50/
and http://hubblesite.org/newscenter/archive/releases/galaxy/elliptical/1995/07/results/50/
Lenticular
have a disk but no arms
have little or no excess gas and dust
Image at http://hubblesite.org/newscenter/archive/releases/galaxy/elliptical/2002/07/results/50/
Irregular Galaxies
any galaxy that isn’t a Spiral, Elliptical, or
Lenticular
usually have lots of gas and dust and young
stars
may have a distorted shape from interaction
with another galaxy
Irregular Galaxies
NASA and NOAO/AURA/NSF Images at
http://hubblesite.org/newscenter/archive/releases/galaxy/irregular/2005/09/results/50/ ,
http://www.noao.edu/image_gallery/html/im0560.html , and http://www.noao.edu/image_gallery/html/im0993.html
Collisions!
We now think that galaxies in groups and
clusters often collide
The Milky Way is moving at 300,000 mph
toward the Andromeda Galaxy
They may collide in about 5 billion years
Stars don’t usually collide
New orbits, gas piles up to form new stars
Interacting
Image from http://hubblesite.org/newscenter/archive/releases/galaxy/interacting/2000/34/results/50/
the Antennae or Mice
Information at http://hubblesite.org/newscenter/archive/releases/galaxy/interacting/1997/34/results/50/
The occasional results of two
galaxies colliding: ringed
galaxies
Images from http://hubblesite.org/newscenter/archive/releases/galaxy/spiral/2002/21/image/a/results/50/ and
http://hubblesite.org/newscenter/archive/releases/galaxy/spiral/1999/16/image/a/results/50/
Supermassive black holes
almost every medium to large galaxy we’ve
check has a supermassive black hole at the
center
the larger the galaxy, the more massive the
black hole
we don’t know which comes first, the galaxy
or the black hole
we think that these black holes are
responsible for some of the galaxies with jets
which give off radio waves, x-rays, etc.
at the center of a large galaxy
Image at http://hubblesite.org/newscenter/archive/releases/exotic/black-hole/1998/22/results/20/ and
http://hubblesite.org/newscenter/archive/releases/exotic/black%20hole/2000/21/image/a/format/web_print/results/20/
Galaxy Clusters
the Local Group
includes the Milky Way, the Andromeda, and over
30 other smaller galaxies
the Virgo Cluster
hundreds to thousands of galaxies, 60 million lightyears away
giant elliptical at center, formed by galactic
cannibalism
the Local Group is “falling” toward the Virgo
Cluster at 60 to 250 miles per second!
Coma Cluster
Image at http://hubblesite.org/newscenter/archive/releases/galaxy/cluster/2008/24/image/a/results/20/
Superclusters!
clusters are bound together in larger structures, called
superclusters
these superclusters have been mapped, and are grouped
into long strings
300 million to a billion light-years long
100 to 300 million light-years wide
and only 10 to 30 million light-years thick
in between these strings are huge voids of galaxies,
although some astronomers may have detected hot gas
Evolution of Galaxies
Image at http://www.galex.caltech.edu/media/glx2007-05f_img01.html