Download Astronomy - Career Account Web Pages

Astronomy
1. Introduction and
Observations
2. Sun and Solar System
3. Stars (Stellar Evolution)
4. Galaxies
An excellent book
on astronomy by
Timothy Ferris
(1988, 2003)
Also,, there are two
excellent periodicals
related to astronomy
– Astronomy and
Sky and Telescope
5. Universe (Deep Space,
Expanding Universe, Hubble
Red Shift, Cosmology)
Astronomy
1. Earth’s position in the solar system
2. Origin of the Universe
3. Natural interest in observing the night sky
Problems in understanding astronomy
concepts
1. Scale (distance and time)
2. Frame of reference (changing and 3-D)
3. Vast distance and time (large numbers and
unfamiliar units/terminology)
Light Year – A unit of distance - “how far light
travels in one year”
Scale of the Universe
Earth orbit
Solar System
Nearest Star
Milky Way Galaxy
Local Group of Galaxies
Observable Universe
300 million km (diameter)
~1 billion km (orbital path)
12 billion km across
(~ 10-3 light years*)
4.27 light years
105 light years
2.5 million light years
13.7 billion light years
* One light year ~1013 km, or ~10 trillion km
(It takes about 1/1000 of a year, or about 9 hours for light
to travel across the solar system; 4.27 years for light from the
nearest star to reach Earth; 434 years for light from Polaris to
reach Earth; and ~105 years for light from the most distant stars
in the Milky Way, our galaxy, to reach Earth)
http://hubblesite.org/newscenter/archive/releases/2004/07/
(~60 MB jpeg file)
Calculate a light year:
~300,000 km/s  the “speed of light”
x60 s/min
~18,000,000 km/min
x60 min/hr
~1,080,000,000
1 080 000 000 km/hr
k /h
x24 hr/day
~25,920,000,000 km/day
x365 days/yr
~9,460,800,000,000 km/yr  speed of light (units = km/yr)
~9,460,800,000,000 km
 One light year (units = km)
So, one light year is approximately 10,000,000,000,000 km,
or,…
1013 km
or,…
10 trillion km
1
Close-up of area in lower right hand corner of previous slide
Hubble Space Telescope (HST)
Ultra Deep Field Image (2003-04)






http://news.discovery.com/space/zooms/oldest-galaxy-universe-hubble-110126.html
Can image 30th magnitude objects.
Required 400 orbits, 11.3 days or recording.
Image contains about 10,000 galaxies.
Area covers 1/12.7 million of the entire sky.
Like looking through an 2 ½ m (8 ft) long soda straw.
With this view, astronomers would need about 50
Ultra Deep Fields to cover the entire Moon.
Hubble's keen vision (0.085 arc seconds) is
equivalent to standing at the U.S. Capitol and seeing
the date on a 400 m (1/4 mile) away at the
Washington monument.
http://www.nasa.gov/mission_pages/hubble/science/ancient-object-gallery.html
2011 Deep space image (after repair/upgrade of Hubble
Space Telescope (HST)
9
10
The Universe's Most Ancient Object
The farthest and one of the very earliest galaxies ever seen in the universe appears as a faint
red blob in this ultra-deep–field exposure taken with NASA's Hubble Space Telescope. This is
the deepest infrared image taken of the universe. Based on the object's color, astronomers
believe it is 13.2 billion light-years away.
The most distant objects in the universe appear extremely red because their light is stretched
to longer, redder wavelengths by the expansion of the universe. This object is at an extremely
faint magnitude of 29, which is 500 million times fainter that the faintest stars seen by the
human eye.
The dim object is a compact galaxy of blue stars that existed 480 million years after the Big
Bang, only four percent of the universe's current age. It is tiny and considered a building
block of today's giant galaxies. Over one hundred such mini-galaxies would be needed to
make up our Milky Way galaxy.
The Hubble Ultra Deep Field infrared exposures were taken in 2009 and 2010, and required
a total of 111 orbits or 8 days of observing. The new Wide Field Camera 3 has the sharpness
and near-infrared light sensitivity that matches the Advanced Camera for Surveys' optical
images and allows for such a faint object to be selected from the thousands of other galaxies
in the incredibly deep images of the Hubble Ultra Deep Field.
Credit: NASA, ESA, G. Illingworth (University of California, Santa Cruz), R. Bouwens
(University of California, Santa Cruz and Leiden University), and the HUDF09 Team
11
12
2
Large Numbers…
Number of stars in the universe (just recently
updated), in at least 3 trillion galaxies.
300 sextillion
(300 x 1021 or,…
or
106
109
1012
1015
1018
1021
3 trillion times 100 billion)
1,000,000
1,000,000,000
1,000,000,000,000
1,000,000,000,000,000
1,000,000,000,000,000,000
1,000,000,000,000,000,000,000
Million
Billion
Trillion
Quadrillion
Quintillion
Sextillion
Stars in Milky Way (spiral) galaxy (left) and in an elliptical
galaxy (right) which contains large numbers of red dwarf
stars.
USAToday, December 2, 2010
Frame of Reference – 3D and constantly changing
(due to Earth’s rotation and seasons caused by tilt of
axis of rotation)
North star
(Polaris)
North star
(Polaris)
Meteor
Time lapse photo
Time lapse photo
http://antwrp.gsfc.nasa.gov/apod/ap991006.html
http://en.wikipedia.org/wiki/North_Star
Time lapse photo
centered on Polaris
(~ 8 hours)
Sun
http://www.opencourse.info/astronomy/introduction/02.motion_stars_sun/northpole_malin.html
Ursa Major (the big bear,
or the big dipper)
We view the stars in the
sky as if they were all
equal distance from
Earth (as on a flat or
spherical surface).
However, the distance to
stars varies greatly.
3
Moons
Jupiter
All of the objects that
we see with the naked
eye in the night sky are
within the Milky Way
galaxy (can see two
other galaxies with
excellent viewing or
binoculars and many
galaxies with a
telescope)
Galileo Galilei
Galileo’s observations of Jupiter’s
moons demonstrated that moons
revolved about a planet providing
support for the Copernican theory
that the Sun was the center of the
solar system.
The constellation Vega
Jupiter and the Galilean Moons as viewed through a
modern amateur telescope (25 cm Meade).
Callisto
Jupiter
p
Europa
Io
Io
Ganymede
Europa
Ganymede
Callisto
Jupiter has at least 63 moons. The largest (and mostly
closest to the planet) were discovered by Galileo in 1610 and
are called the Galilean moons
http://en.wikipedia.org/wiki/Moons_of_Jupiter
http://en.wikipedia.org/wiki/Moons_of_Jupiter
Kepler’s 3rd law:
P2 ~ D3
Ganymede
Jupiter
 Nights
Period squared is
proportional to Distance
cubed. The exact
equation can be used to
calculate the mass of a
planet:
Period
(days)
Distance
(km)
Johannes
Kepler
http://kepler.nasa.gov/files/mws/OrbitsOfJupitersMoons.pdf
Sky and Telescope javascript Jupiter’s moons orbit calculator:
http://www.skyandtelescope.com/wp-content/observingtools/jupiter_moons/jupiter.html#
4
Close-up of Galilean Moons positions relative to Jupiter on the date and time
shown (C = Callisto, E = Europa, I = Io, G = Ganymede). With the calculator
(below) you can step through time (use 10 minute or 1 hour time steps) to see
the orbits of the moons about Jupiter (viewed from Earth, approximately along
the plane of the ecliptic.
Sky and Telescope javascript Jupiter’s moons orbit calculator:
http://www.skyandtelescope.com/wp-content/observingtools/jupiter_moons/jupiter.html#
Moon rotating (animation from multiple images from the NASA LRO (Lunar
Reconnaissance Orbiter): http://www.youtube.com/watch?v=sNUNB6CMnE8.
The moon does rotate about once every 27 days so that we always see the
same “side” of the Moon. The rotation rate is cause by gravitational “locking” of
the Moon to the Earth. It tool 4 years of observations to gather the images for
the animation.
The Solar System (Sun and planets
not to scale; Figure 15.17, text)
Orbits to scale
The Moon as it appears from Earth (northern hemisphere):
http://en.wikipedia.org/wiki/Moon
Orrery
Orrery
An excellent online Orrery (for viewing the planets in orbit)
can be found at: http://gunn.co.nz/AstroTour - main controls
model planet
(Orrery)
note
that(also:
it is
areSolar
speed,system
orbit brightness,
size–and
zoom.
An excellent online Orrery (for viewing the planets in orbit)
can be found at: http://gunn.co.nz/AstroTour - main controls
are speed, orbit brightness, planet size and zoom. (also:
http://www.pbs.org/wgbh/nova/space/tour-solar-system.html)
not at true scale in distances or diameters!
http://www.pbs.org/wgbh/nova/space/tour-solar-system.html)
29
30
5
Another view of the Solar System
A Brief Tour of the Solar System
The Sun and planets drawn to scale (orbital
positions not to scale) Figure 15.18, text)
The Sun and planets drawn to scale (orbital position not to
scale) (http://en.wikipedia.org/wiki/Planet).
32
The gas giant planets (Jovian planets)
The terrestrial planets
Note sunspots
The Sun and planets drawn to scale (orbital position not to
scale) (http://en.wikipedia.org/wiki/Planet).
Figure 15.19, text
33
The Sun and planets drawn to scale (orbital position not to
scale) (http://en.wikipedia.org/wiki/Planet).
34
Earth’s Moon
(Figure 15.23, text)
6
Mars (Figures 15.29 and 15.30, text)
Olympus Mons (and outline of
Arizona for scale)
Jupiter (and great red spot) (Figure 15.33, text)
Saturn (and rings) (Image from Hubble Space
telescope; Figure 15.36, text)
“On July 19, 2013, in an event celebrated the world over, NASA's Cassini spacecraft
slipped into Saturn's shadow and turned to image the planet, seven of its moons, its
inner rings -- and, in the background, our home planet, Earth.” (http://www.nasa.gov/
mission_pages/cassini/whycassini/jpl/cassini20131112.html#.UoTHPD8wLpf)
Moon
Zoom in to see Earth and Moon
Neptune (and great dark spot) (Figure 15.40, text)
7
Comet (dust and ion tail) orbiting the Sun (Figure
15.43, text)
Asteroid Eros (Figure 15.42, text)
Planets and Solar System Websites
Viewing the Night Sky
Observing Stars – Apparent Magnitude
(brightness; what we see without
adjusting for distance to the star) and
Absolute Magnitude (brightness
adjusted for distance).
The Sun has a brightness (apparent
magnitude of -27; note that smaller
magnitudes are brightest).
http://www.nasa.gov/worldbook/planet_worldbook_update.html
http://en.wikipedia.org/wiki/Planet
http://pds.jpl.nasa.gov/planets/
http://www.space.com/planets/
http://science.nationalgeographic.com/science/space/solar-system
http://www.buzzfeed.com/daves4/the-universe-is-scary
45
Faintest stars:
Apparent Magnitude
Naked Eye viewing
6
Binoculars
10
Amateur Telescopes
15
Modern Large Telescopes 25
8
Measuring Distance to Stars: 1. The Stellar Parallax method
Example of lunar parallax: Occultation of Pleiades by the Moon
This is the method referred to by Jules Verne in From the Earth to the Moon:
(Figure 16.2, text)
Stellar Parallax – distance determined from parallax angle, the
smaller the parallax angle the greater the distance to the star. A
parallax angle of 1 second of arc (1/3600 degrees angle)
corresponds to a distance of 3.09 x 1013 km and is called one
Parsec. Distant stars are measured in MegaParsecs.
Measuring Distance to Stars: 1. The Stellar Parallax method
Another method is to take two pictures of the Moon at
exactly the same time from two locations on Earth and
compare the positions of the Moon relative to the stars.
Using the orientation of the Earth, those two position
measurements, and the distance between the two locations
on the Earth, the distance to the Moon can be triangulated:
This is the method referred to by Jules Verne in From
the Earth to the Moon.
http://en.wikipedia.org/wiki/File:Stellarparallax2.svg
Measuring Distance to Stars: 2. Brightness method
(Figure 16.2, text)
Stellar Parallax – Animation available at:
http://www.astro.ubc.ca/~scharein/a311/Sim.html
Variable Stars – Certain stars that have used up their main
supply of hydrogen fuel are unstable and pulsate. RR Lyrae
variables have periods of about a day. Their brightness doubles
from dimest to brightest. Cepheid variables have longer periods,
from one day up to about 50 days. Their brightness also doubles
from dimest to brightest.
Period ~3 days
Measure the
M
th
period of the
variable star, then
… see next slide
Light spreads out with distance such that the
brightness varies by 1/r2, where r is the
distance. For example in the diagram above,
the brightness at 4 m distance would be only
1/16th of the brightness at 1 m.
Empirical relationship (determined by observations of stars having a
known distance) between period of pulsation for variable stars and
luminosity. Absolute magnitude for a star whose distance is unknown
can be calculated from the determined luminosity and then the distance
to the star calculated from the brightness method using the absolute
and apparent magnitude and 1/r2 relationship.
Period ~3 days
y
indicates a
luminosity
(proportional to
absolute
magnitude) of
about 500.
http://zebu.uoregon.edu/~soper/MilkyWay/cepheid.html
9
American astronomer Henrietta Leavitt observed many Cepheid
variables in the Small Magellanic Cloud (a satellite galaxy to
ours). She found the period-luminosity relation (below; reported
in 1912). (http://zebu.uoregon.edu/~soper/MilkyWay/cepheid.html )
Period ~3 days
y
indicates a
luminosity
(proportional to
absolute
magnitude) of
about 500.
Measuring Distance to Stars: 2. Brightness method
Brightness Demo…  Absolute Brightness = 1, 
Observer

Distance  Stars
Star A
o
Star B

 Star B is twice as far as A
The apparent brightness of A and B will be the same
Star C

Absolute Brightness = 4
Star D
 Star D is twice as far as C

The apparent brightness of C will be 16 times as great D
The Sun – A Typical Star
The sun is one of over 100 billion stars in
the Milky Way Galaxy. It is about 25,000
light-years from the center of the galaxy,
and it revolves around the galactic center
once about every 250 million years.
The sun is a star with a diameter of
approximately 1,390,000 km, about 109
times the diameter of Earth. The largest
stars have a diameter about 1,000 times
that of the sun.
sun
Main composition of the Sun
Hydrogen
73.46%
Helium
24.85%
Oxygen
0.77%
Carbon
0.29%
Iron
0.16%
Spectacular loops and
prominences are often visible on
the Sun's limb.
http://nineplanets.org/sol.html
Comprising about 99.8632% of the total mass of the Solar System –
most of the remainder is Jupiter.
Fewer than 5 percent of the stars in the Milky Way are brighter or more
massive than the sun. But some stars are more than 100,000 times as
bright as the sun, and some have as much as 100 times the sun's
mass. At the other extreme, some stars are less than 1/10,000 as
bright as the sun, and a star can have as little as 7% of the sun's mass.
There are hotter stars, which are much bluer than the sun; and cooler
stars, which are much redder.
http://www.nasa.gov/worldbook/sun_worldbook.html
Nuclear Fusion in the Sun
(and other stars) – the
proton-proton chain reaction:
Note that the process starts
with 4 protons and ends with
one atom of helium-4 (4
protons are fused into one
helium-4 atom) plus large
energy release – the gamma
particles that eventually
convert to photons
(electromagnetic radiation, or
light).
http://en.wikipedia.org/wiki/Sun
http://en.wikipedia.org/wiki/Nuclear_fusion
10
Nuclear Fusion in the Sun
(and other stars) – the
proton-proton chain reaction:
Nuclear Fusion in the Sun
(and other stars) – the protonproton chain reaction:
The decrease in mass (from
4 protons to 2 protons and 2
neutrons) is only 0.7% but
the energy release is large
because of the equation
e=mc2.
The proton–proton chain occurs
around 9.2×1037 times each
second in the core of the Sun.
The Sun releases energy at the
mass-energy conversion rate of
4.26 million metric tons per
second, (3.846×1026 W) or
9.192 × 1010 megatons of TNT
per second.
Also note that at the end of
the reaction, there are still
two protons remaining, so the
reaction continues as a chain
reaction always releasing
energy.
http://en.wikipedia.org/wiki/Nuclear_fusion
Nuclear Fusion in the Sun
(and other stars) – the
proton-proton chain reaction:
Energy from nuclear fusion in
stars larger than the Sun
(hotter and higher pressure
core) is generated by the
Carbon-Nitrogen-Oxygen
(CNO), or other, chain
reaction.
(http://en.wikipedia.org/wiki/Sun)
http://en.wikipedia.org/wiki/Nuclear_fusion
Tools of Astronomy:
1. Samples – meteorites (abundance of elements).
2. Photography – telescopes (Earth-based and satellite;
visible and invisible wavelengths)
3. Distance measurement – stellar parallax, brightness
method (variable stars)
stars), Hubble red shift
shift.
4. Brightness – absolute and apparent magnitude
(classification).
5. Spectroscopy – continuous spectrum (amount of radiation
at different wavelengths; provides temperature of surface of
star), bright line and dark line spectra (provides
composition).
64
http://en.wikipedia.org/wiki/Nuclear_fusion
Life Cycle of the Sun
In about another 5 billion years, the hydrogen will be nearly
depleted and the Sun’s core will collapse and heat up resulting
in helium fusion and the Sun will become a Red Giant with a
size that will probably extend out to the present orbit of Mars.
http://en.wikipedia.org/wiki/File:Solar_Spectrum.png
http://en.wikipedia.org/wiki/Sun
11
Sunspots are
temporary
phenomena on
the photosphere
of the Sun that
appear visibly as
dark spots
compared to
surrounding
regions. They are
caused by intense
magnetic activity,
which inhibits
convection,
forming areas of
reduced surface
temperature.
Note 11 year cycle of sunspots
http://en.wikipedia.org/wiki/Sunspot
http://en.wikipedia.org/wiki/Sun
Very bright stars have more shorter-wavelength radiation and
higher temperatures. These measurements are from
spectrometers.
http://csep10.phys.utk.edu/astr162/lect/sun/spectrum.html
http://en.wikipedia.org/wiki/Sunspot
The Hertzsprung-Russell (H-R) Diagram
The Hertzsprung-Russell (H-R) Diagram
(Figure 16.7, text)
Surface Temperature (K)
Sun
“Classification of Stars”
(Figure 16.7, text)
Absolute M
Magnitude
Luminosity
y (Sun = 1)
Sun
Absolute M
Magnitude
Luminosity
y (Sun = 1)
Hotter stars have
shorter wavelength
radiation and shorter
lifetimes
Cooler stars have
longer wavelength
radiation and longer
lifetimes
Surface Temperature (K)
12
Low Mass
(Figure 16.12, text)
Medium Mass
High Mass
(Figure 16.11, text)
H-R diagram illustrating life cycle of a main
sequence star (such as the Sun). Most of lifetime,
star is on Main Sequence, then in dwarf stage.
Life cycle of stars
74
Supernova remnant Cassiopeia A located about 10,000 light
years from Earth.
Trifid Nebula (birthplace of Stars, mostly H and He gases
illuminated by hot young stars).
Neutron Star
(Figure 16.8, text)
(Figure 16.6, text)
Horsehead (mostly dark) Nebula in constellation Orion.
(Figure 16.10, text)
The Helix Planetary Nebula (formed during a star’s
collapse from a red giant to a white dwarf).
(Figure 16.13, text)
13
The Crab Nebula (in the constellation Taurus;
the remains of the supernova explosion of A.D.
1054).
The Veil Nebula (in the constellation Cygnus;
the remains of a supernova implosion).
(Figure 16.15, text)
(Figure 16.14, text)
Spiral Galaxy M81 (NASA)
Galaxies – Typically consist of 1 billion to over 100 billion
stars. Most are relatively flat. Stars in the galaxy revolve
around a central area, and thus don’t collapse from gravity
(similar to the solar system). Most galaxies (including the
Milky Way) probably have black holes in the center of the
galaxy accounting for a substantial part of its mass.
Types of Galaxies: Elliptical, Spiral, Irregular, Dwarf
A tour of some galaxies…
(Chapter 16, text)
Spiral Galaxy Andromeda
(Figure 16.17, text)
Above: The Milky
(panorama from
Wayy (p
Earth).
Right: Spiral galaxy
NGC 2997 (similar to
Milky Way).
(Figure 16.20, text)
(Figure 16.19, text)
14
The Barred spiral galaxy
Elliptical galaxy ESO 325-G004. Most
elliptical galaxies are very old and probably
result from two galaxies colliding.
(Figure 16.22, text)
http://en.wikipedia.org/wiki/Elliptical_galaxy
Cosmic Web (structure of the universe, how the
galaxies are distributed in the universe) Videos –
86
Measuring Distance to Stars (and Galaxies): 3. The
Hubble Red Shift (a Doppler Effect)
Moving object emitting radiation
Where the Galaxies Are – Margaret Geller, 1991
NASA /Goddard Space Flight Center Scientific Visualization
Center:
Cosmic Origins Spectrograph: Large Scale Structure of the Universe
http://svs.gsfc.nasa.gov/vis/a010000/a010200/a010223/index.html
Journey Through the Cosmic Web
http://svs.gsfc.nasa.gov/vis/a010000/a010100/a010118/index.html

Observer here
sees longer
wavelength
radiation (red
shifted)
Motion

Observer here
sees shorter
wavelength
radiation (blue
shifted)
Doppler Effect (and Red Shift) – Animation available at:
http://www.astro.ubc.ca/~scharein/a311/Sim.html
Measuring Distance to Stars (and Galaxies): 3. The
Hubble Red Shift (a Doppler Effect)
Moving object emitting radiation
Example of Doppler Effect – Observer senses different
wavelengths (hears different sounds) from approaching and
receding ambulance. Note that the ambulance moving away
results in longer wavelengths. The faster the ambulance is
moving away, the lower the wavelength.
(Figure 16.22, text)

Observer here
sees longer
wavelength
radiation (red
shifted)
Motion

Observer here
sees shorter
wavelength
radiation (blue
shifted)
Doppler Effect (and Red Shift) – Animation available at:
http://www.astro.ubc.ca/~scharein/a311/Sim.html
15
Hubble’s Law
Hubble’s Law
Hubble, 1929
Hubble's law is a statement of a direct correlation between the
distance to a galaxy and its recessional velocity as determined by the
red shift. It can be stated as:
H0 is the slope of the line
http://hyperphysics.phy-astr.gsu.edu/hbase/astro/hubble.html
http://hyperphysics.phy-astr.gsu.edu/hbase/astro/hubble.html
Modern Hubble’s
Law Data
1) Virtually all
galaxies are moving
away from us, e.g.
they are redshifted.
2) The more distant
galaxy,
y, the larger
g
the g
its redshift, that is the
faster it is moving
away.
Hubble’s original 1929 data
http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/bigbang.htm
1
B 2
C
Expanding universe modeled as the
surface of a balloon - Imagine a balloon
with points A, B and C labeled. After
expanding the balloon, the distances
change.
Time 1
2
From Time 1 to Time 2,,
B
increase in distance A
4
to B is 1, A to C is 2. So,
velocity for A to C is
twice is large as from A
to B. More distant
C
objects have higher
recession velocity. This
is true for all locations
on the surface.
Distances in Red
At all locations,
objects are
moving away and
more distant
objects have
higher recession
velocity.
Expanding Universe – As the universe expands, the
galaxies get farther apart (although some are
gravitationally connected and collide/merge) and
increase their red shift.
One MegaParsec (Mpc) = 3 million light years = 3 x 1019 km
A
The reported value of the Hubble parameter has varied widely over the
years, testament to the difficulty of astronomical distance measurement.
But with high precision experiments after 1990 the range of the reported
values has narrowed greatly to values in the range of:
http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/bigbang.htm
Cosmic Microwave Background Radiation
A
Time 2
Observations of background radiation of the universe from the 1990 NASA
COBE (Cosmic Background Explorer) satellite
http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation
95
16
Cosmic Microwave Background
Radiation
Cosmic Microwave Background
Radiation
With a traditional optical telescope, the space between stars and
galaxies (the background) is pitch black. But with a radio telescope,
there is a faint background glow, almost exactly the same in all
directions, that is not associated with any star, galaxy, or other object.
This glow is strongest in the microwave region of the radio spectrum,
hence the name cosmic microwave background radiation. The
CMB's serendipitous discovery in 1964 by American radio
astronomers Arno Penzias and Robert Wilson was the culmination of
work initiated in the 1940s, and earned them the 1978 Nobel Prize.
http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation
The CMBR is well explained as
radiation left over from an early stage
in the development of the universe, and
its discovery is considered a landmark test of the Big Bang model of
the universe. When the universe was young, before the formation of
stars and planets, it was smaller, much hotter, and filled with a
uniform glow from its white-hot fog of hydrogen plasma. As the
universe expanded, both the plasma and the radiation filling it grew
cooler. When the universe cooled enough, stable atoms could form.
These atoms could no longer absorb the thermal radiation, and the
universe became transparent instead of being an opaque fog. The
photons that existed at that time have been propagating ever since,
though growing fainter and less energetic, since exactly the same
photons fill a larger and larger universe. This is the source for the
term relic radiation, another name for the CMBR.
http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation
Evidence for Big Bang Theory
Red Shift, universe expanding
Two of COBE's principal
investigators, George Smoot
and John Mather, received the
Nobel Prize in Physics in 2006
for their work on precision
measurement of the CMBR.
http://www.astro.ucla.edu/~wright/CMB.html
The Cosmic Microwave Background Radiation measured by the COBE
satellite almost precisely fits the backbody radiation curve corresponding to
2.725 K (-270.425 oC) – a very cold temperature due to cooling of the
universe (in the space between galaxies and stars) and red shift.
Black Holes
A black hole is a region of space whose gravitational force is so strong that
nothing can escape from it. A black hole is invisible because it even traps
light. The fundamental descriptions of black holes are based on equations
in the theory of general relativity developed by the German-born physicist
Albert Einstein. The theory was published in 1916.
Characteristics of black holes
The gravitational force is strong near a black hole because all the black
hole's matter is concentrated at a single point in its center. Physicists call
this point a singularity. It is believed to be much smaller than an atom's
nucleus.
The surface of a black hole is known as the event horizon. This is not a
normal surface that you could see or touch. At the event horizon, the pull
of gravity becomes infinitely strong. Thus, an object can exist there for only
an instant as it plunges inward at the speed of light.
http://www.nasa.gov/worldbook/blackhole_worldbook.html
Distant galaxies receding faster
Cosmic background radiation
Abundance of elements in the universe is consistent with
mathematical models and nuclear physics of Big bang
evolution of the universe
Einstein’s general theory of relativity predicts expanding
universe
Formation of galaxies and large scale structure of the universe
Black Holes
Formation of black holes
According to general relativity, a black hole can form when a massive star
runs out of nuclear fuel and is crushed by its own gravitational force.
While a star burns fuel, it creates an outward push that counters the
inward pull of gravity. When no fuel remains, the star can no longer
support its own weight. As a result, the core of the star collapses. If the
mass of the core is three or more solar masses, the core collapses into a
singularity in a fraction of a second.
Galactic black holes
Most astronomers believe that the Milky Way Galaxy -- the galaxy in which
our solar system is located -- contains millions of black holes. Scientists
have found a number of black holes in the Milky Way. These objects are
in binary stars that give off X rays. A binary star is a pair of stars that orbit
each other.
http://www.nasa.gov/worldbook/blackhole_worldbook.html
17
Black Holes
Supermassive black holes
Scientists believe that most galaxies have a supermassive black hole at the
center. The mass of each of those objects is thought to be between 1
million and 1 billion solar masses. Astronomers suspect that supermassive
black holes formed several billion years ago from gas that accumulated in
the centers of the galaxies.
Th
There
iis strong
t
evidence
id
th
thatt a supermassive
i bl
black
kh
hole
l lilies att th
the center
t
of the Milky Way. Astronomers believe this black hole is a radio-wave
source known as Sagittarius A* (SgrA*). The clearest indication that SgrA*
is a supermassive black hole is the rapid movement of stars around it. The
fastest of these stars appears to orbit SgrA* every 15.2 years at speeds that
reach about 3,100 miles (5,000 kilometers) per second. The star's motion
has led astronomers to conclude that an object several million times as
massive as the sun must lie inside the star's orbit. The only known object
that could be that massive and fit inside the star's orbit is a black hole.
http://www.nasa.gov/worldbook/blackhole_worldbook.html
Because black holes are invisible, they are mostly detected
(inferred) form the gravitational forces required for objects
which revolve around them and from radiation from nearby
regions (outside the event horizon) that are energized by the
rapid motion of objects and gases and emit x-ray radiation.
Some useful references:
Chaisson, E., Relatively Speaking: Relativity, Black Holes, and the Fate of the
Universe, W.W. Norton & Company, New York, 254 pp., 1988.
Ferris, T., Coming of Age in the Milky Way, Anchor Books, New York, 495 pp.,
1988.
http://www.nasa.gov/worldbook/blackhole_worldbook.html
18