Transcript Stars and Galaxies

Stars, The
Universe
and
Galaxies
Image at http://hubblesite.org/newscenter/archive/releases/galaxy/spiral/2009/07/image/g/results/50/
What are we going to cover?
Classifying Stars
History of the Universe
Classifying Galaxies
Different
types of
stars
Image from
http://hubblesite.org/newscenter/archive/releases/star%20cluster/globular/2003/21/image/a/results/50/
Types of Stars
Big
Small
Red
Blue
Yellow
In groups
Life Cycle of a star
Nebula
Low mass star
Main Sequence
Red Giant
White dwarf
High-mass star
main sequence
red supergiant
supernova
Neutron star / black hole
Magnitude of stars
Absolute Magnitude- a measure of the
amount of light a star gives off (luminosityhow bright)
Apparent Magnitude- amount of light
received on Earth (the way it appears to us)
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 our Milky
Way Galaxy
Different types
Orion image at http://hubblesite.org/newscenter/archive/releases/2006/01/image/a/results/50/
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/
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/
Young stars
and some
planets form
in nebular
cloud
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/
Neutron Star or Pulsar
Image at http://hubblesite.org/newscenter/archive/releases/nebula/supernova-remnant/2002/24/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/
Leftovers from an Explosion
Supernova remnant
(smaller, less gas)
Image at http://hubblesite.org/newscenter/archive/releases/nebula/supernova-remnant/2005/37/results/50/
H-R Diagram
Indicates differences and relationships
between stars
Horizontal axis = surface temp
Vertical axis = Luminosity-absolute
magnitude (brightness)
Sun rests in the middle-we use for
comparison
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
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
Our Sun
•Regular/medium
sized star
•On edge of a
disc shaped
galaxy (Milky
Way)
Image at http://www.gsfc.nasa.gov/topstory/20011210insidesun.html
Our Sun
On the “Main Sequence”(continuous and distinctive
band of stars that appears on plots of stellar color
versus brightness )
Nuclear Fusion reactions (2 atoms jammed togetherenergy emitted as light and heat)- converts
600,000,000 tons of hydrogen into helium every second
Many thousands of times closer to Earth than any other
star
A planet’s characteristics are often determined by
distance from the Sun (ex- rocky, gaseous,
temperature)
In a few Billion years… Red
Giant
Image at http://hubblesite.org/newscenter/archive/releases/1997/26/image/a/
By 5 billion years… White
Dwarf
Small, but very hot
Image at http://hubblesite.org/newscenter/archive/releases/nebula/planetary/1998/39/results/50/
Building a Universe
Instantaneous filling of
space with all matter
What is our Universe made of?
 Stars and planets
 Gas and dust
 Organized into star clusters
 Organized into nebulae
 Organized into galaxies
 Other things:
 Black holes
 Dark matter
 Dark energy
Image from
http://galileo.rice.edu/lib/student_work/astronomy95/orionpleiades.html
When Did the Universe Form?
Cosmic background radiation
temperature on celestial sphere
 ~13.7 billion years ago
 How do we know?
Spreading (Red Shift) know distances, rates of
retreat, relative positions
Pervasive background
radiation of 2.7°C above
absolute zero - afterglow
of the Big Bang
http://timeline.aps.org/APS/resources/85_06a.jpg
History of the
Universe
•10-43 seconds - gravity separates from other forces
•10-35 to 10-32 seconds - fundamental particles - quarks and electrons
•10-6 seconds - quarks combine into protons and neutrons
•1 second - electromagnetic and weak nuclear forces separate
•3 minutes - protons and neutrons combine into atomic nuclei
•105 years - electrons join nuclei to make atoms; light is emitted
•105-109 years - matter collapses into clouds, making galaxies and stars
Orion Nebula - http://stardate.utexas.edu/resources/ssguide/planet_form.html
History of the Universe
Image from http://dsc.discovery.com/space/top-10/strange-universe/space-10-weirdest-things-universe-10.html
Later History
Image at http://www.galex.caltech.edu/media/glx2004-01r_img02.html
Big Bang Theory
 In 1915, Albert Einstein concluded that the
universe could not be static based on his
recently-discovered theory of relativity and
added a "cosmological constant" to the
theory of relativity because astronomers
assured him that the universe was static
 Aleksandr Friedmann and Abbe George
LeMaitre are credited with developing the
basics of the Big Bang model between 1922
and 1927; their calculations suggested that
universe is expanding, not static.
 Years later, Einstein called his cosmological
constant the biggest mistake of his career
Image at http://map.gsfc.nasa.gov/universe/bb_theory.html
Expanding Universe
 In 1929, Edwin Hubble showed that most
galaxies are red-shifted (moving away
from us), and that a galaxy’s velocity is
proportional to its distance (galaxies that
are twice as far from us move twice as
fast)
Image from http://imagine.gsfc.nasa.gov/docs/science/mysteries_l1/origin_destiny.html
Hubble’s Evidence
 Doppler shifting - wavelength emitted by something moving away
from us is shifted to a lower frequency
 Sound of a fire truck siren - pitch of the siren is higher as the fire
truck moves towards you, and lower as it moves away from you
 Visible wavelengths emitted by objects moving away from us are
shifted towards the red part of the visible spectrum
 The faster they move away from us, the more they are redshifted.
Thus, redshift is a reasonable way to measure the speed of an
object.
 When we observe the redshift of galaxies, almost every galaxy
appears to be moving away from us – the Universe is expanding.
Origin of the Universe
Data collected (from Hubble
Telescope) is used as evidence to
help develop scientific theories
Big Bang
Dominant scientific theory about the
origin of the universe
Occurred ~13.7 billion years ago
What is the Big Bang?
Infinitely dense point
not governed by our
physical laws or time
All matter and energy
contained in one point
Image from http://www.newscientist.com/articleimages/dn11799/0-didantimatter-factory-spark-brightest-supernova.html
Predictions for the Big Bang
Model
The expansion of the Universe
 Edwin Hubble's 1929 observation that galaxies were generally
receding from us provided the first clue that the Big Bang theory
might be right.
The abundance of the light elements H, He, Li
 The Big Bang theory predicts that these light elements should have
been fused from protons and neutrons in the first few minutes after
the Big Bang.
The cosmic microwave background (CMB) radiation
 The early universe should have been very hot. The cosmic
microwave background radiation is the remnant heat leftover from
the Big Bang.
Evidence for Big Bang
 Red shift - as light from distant galaxies approach earth there is an
increase of space between earth and the galaxy, which leads to
wavelengths being stretched
 In 1964, Arno Penzias and Robert Wilson, discovered a noise of
extraterrestrial origin that came from all directions at once radiation left over from the Big Bang
 In June 1995, scientists detected helium in the far reaches of the
universe - consistent with an important aspect of the Big Bang
theory that a mixture of hydrogen (75%) and helium (25%) was
created at the beginning of the universe
Measuring Distances
What is a Light Year?
 A light year is the distance light travels in a year. Light moves at a
velocity of about 300,000 kilometers (km) each second;
 Astronomical Unit:150 million Kilometers
Why do we use light years?
 We need numbers that make sense to us in relationship to objects;
we scale up and use meters and kilometers for large numbers.
 Distances between stars and galaxies
 Different wavelengths of Electromagnetic spectrum are used to
gain information about distances and properties of components in
the universe
What is a “galaxy”?
A large group of stars outside of our own Milky Way
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/
Galaxies
come in different sizes (dwarf, large, giant)
come in different shapes and classifications
Spirals
Ellipticals
Irregulars
are fairly close together, relative to their
sizes
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/
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
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 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
Spiral
Galaxy
on
Edge
Image at http://hubblesite.org/newscenter/archive/releases/galaxy/spiral/2006/24/image/a/results/50/
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
Mapping the Milky Way
How do we know what our Galaxy
looks like?
We can see stars
 star clusters
 nebulae
 Galaxies
 Let’s try to Map our Galaxy
The Milky Way
Image at http://news.nationalgeographic.com/news/bigphotos/1945371.html
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
Irregular Galaxies
any galaxy that isn’t a Spiral, Elliptical
usually have lots of gas and dust and young
stars
may have a distorted shape from interaction
with another galaxy
Active
galaxy
Image at http://hubblesite.org/newscenter/archive/releases/galaxy/spiral/2000/37/results/50/
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/