Transcript NATS 1311 From the Cosmos to Earth

NATS1311 From the Cosmos to Earth
ATOM
DEFINITION:
The smallest unit of a chemical element that has the
properties of the element.
The atom consists of a nucleus with orbiting electrons
surrounding the nucleus.
NATS 1311 From the Cosmos to Earth .
Nuclear stability
diagram.
Number of
neutrons vs.
number of protons
in a nucleus.
NATS 1311 From the Cosmos to Earth
Radioactive Decay Processes
4
U 234
Th
90
2
alpha decay
238
92
beta minus decay
14
6
14
7
0
1
electron capture
7
4
0
1
7
3
beta plus decay
14
8
C N 
Be e Li
O  N 
14
7
0
1
Changes number of protons and neutrons in decaying
nucleus
Type of decay protons neutrons
nucleons

-2
-2
-4
+1
-1
0
ec
-1
+1
0
+
-1
+1
0

0
0
0
 = gamma ray emission from nucleus
NATS 1311 From the Cosmos to Earth
Half life
The time required for one half of a group of nuclei to
decay into their daughter products.
Sometimes called lifetime.
NATS 1311 From the Cosmos to Earth .
NATS 1311 From the Cosmos to Earth
RADIOACTIVE ISOTOPES USED IN GEOCHRONOLOGY
URANIUM  LEAD
238
U  206PB
HALF LIFE: 4.5 BILLION YEARS
STRONTIUM  RUBIDIUM
87
SR  87RB
HALF LIFE: 47 BILLION YEARS
POTASSIUM  ARGON
40
K  40AR
HALF LIFE: 1.3 BILLION YEARS
CARBON  NITROGEN
14
C  14N
HALF LIFE: 5500 YEARS
NATS 1311 From the Cosmos to Earth
Besides radioactive decay of an unstable nucleus, nuclei
undergo two other process to change for one element
to another.
These are fission and fusion.
Fission:
Breaking apart a heavy nucleus into two lighter nuclei.
U  n U  Sr Xe 2n  E
235
92
236
92
94
38
140
54
Requres a neutron to activate the process.
NATS 1311 From the Cosmos to Earth .
NATS 1311 From the Cosmos to Earth
Besides radioactive decay of an unstable nucleus, nuclei
undergo two other process to change for one element to
another.
These are fission and fusion.
Fusion:
Combination of light nuclei into a heavier nucleus producing
a large quantity of energy.
4 hydrogen atoms combine into 1 helium atom.
This process requires extremely high temperatures and
pressures and occurs in the core of stars.
NATS 1311 From the Cosmos to Earth .
NATS 1311 From the Cosmos to Earth
Nuclear fission and fusion
Binding energy
Energy equivalent to missing mass of a nucleus.
Mass of hydrogen atom
Add mass of a neutron
Mass of deuterium atom
Missing mass
1.0078 amu
1.0087 amu
2.0165 amu
2.0141 amu
0.0024 amu
1 amu (atomic mass unit) = 931 MeV
from E= m c2
Therefore 0.0024 amu = 2.2 Mev = 3.5x10-13 Joules
This is called the binding energy of deuterium
NATS 1311 From the Cosmos to Earth
1 gram of hydrogen produces 1 x 1011 Joules of energy.
Enough to boil 50 tons of water.
Binding energy per nucleon :
(the number of protons and neutrons in the Nucleus)
Total binding energy of atom
Number of nucleons in atom
NATS 1311 From the Cosmos to Earth .
Triple alpha process. Three helium atoms combine to
form 1 carbon atom.
NATS 1311 From the Cosmos to Earth .
C-N-O Process.
4 Hydrogen atoms
are added, one at
a time to 12C, 13C,
14N, and 15N.
The end products
are 12C and a
Helium atom.
The net result is 4
hydrogen atoms
form 1 helium
atom.
NATS 1311 From the Cosmos to Earth
Element building
The process of element bulding continues by
adding the nucleus of one helium atom at a time to
12C until 56Fe (Iron-56) is obtained.
12C +4He -›16O
6
2
8
16O + 4He -› 20Ne
8
2
l0
20Ne +4He -› 24Mg
l0
2
l2
•
•
•
52Cr
4
56Fe
24 + He2 -›
26
The process stops here.
• maximum stability is reached
• the next element has a lower binding energy
and greater relative nuclear mass.
NATS 1311 From the Cosmos to Earth FIG. 14.16
Figure 14.16
Overall, the average
mass per nuclear
particle declines
from hydrogen to
iron and then
increases. Selected
nuclei are labeled to
provide reference
points. (This graph
shows the most
general trends only;
a more detailed
graph would show
numerous up-anddown bumps
superimposed on
the general trend.)
NATS 1311 From the Cosmos to Earth FIG. 14.18
Figure 14.18
This graph shows the
observed relative
abundances of elements
in the galaxy in
comparison to the
abundance of hydrogen.
For example, the
abundance of nitrogen is
about 10-4, which means
that there are about 10-4
(=0.0001) times as many
nitrogen atoms in the
galaxy as hydrogen
atoms.
NATS 1311 From the Cosmos to Earth .
LAWS OF RADIATION
Black body:
An ideal object that absorbs all radiant energy that
reaches its surface. It also emits radiation, the
characteristics of which depend on its temperature.
Planck's law:
Planck developed a mathematical formula that explained
radiation from black bodies.
He assumed light existed in small quanta called photons
E = hf
where
h = Planck's constant
f = frequency of vibration
NATS 1311 From the Cosmos to Earth .
Spectrum:
The amount of radiation given off at each wavelength.
Stefan's law: (Rule 1)
The energy emitted by a black body is proportional to
the fourth power of its absolute temperature
E ~T4
Wien's law: (Rule 2)
The wavelength at which most energy is emitted from
a black body is inversely proportional to its absolute
temperature.
NATS1311 From the Cosmos to Earth FIG. 6.10
Figure 6.10 Graphs of idealized thermal radiation spectra.
Note that, per unit surface area, hotter objects emit more
radiation at every wavelength, demonstrating Rule 1 for
thermal radiation. The peaks of the spectra occur at shorter
wavelengths (higher energies) for hotter objects,
demonstrating Rule 2 for thermal radiation.
NATS 1311 From the Cosmos to Earth
Temperature
(K) of Black
Body
Wavelength (max) at
Which Most Radiation is
Emitted
Type of Radiation
3
0.1 cm
Radio waves
300
0.001 cm
"Far" Infrared
3,000
1000 nm
"Near" Infrared
4,000
750 nm
Red Light
6,000
500 nm
Yellow Light
8,000
375 nm
Violet Light
10,000
300 nm
"Near" Ultraviolet
30,000
100 nm
"Far" Ultraviolet
300,000
10 nm
"Soft" X-Rays
1.5 million
20 nm
"hard" x-rays
3 billion
0.001 nm
Gamma rays
NATS 1311 From the Cosmos to Earth .
Spectral classes of stars
Spectral
Class
O
B
A
F
G
K
M
Intrinsic
color
electric blue
blue
blue white
yellow white
yellow
orange
red
Effective
temperature*
38,000
30,000
10,800
7,240
5,920
5,240
3,920
*For the hottest spectral type in class,
such as A0 in class A.
Each class is divided into 10 subgroups labeled 0 - 9.
For example, B0 (hottest), or B9 (coolest) in class B.
NATS 1311 From the Cosmos to Earth
LUMINOSITIES
Luminosity:
~ r2T4
Apparent magnitude:
Apparent brightness of a
celestial body based on a
logarithmic scale of luminosity.
Magnitude scale:
1 is 2.5:1
2 is 6.3:1
5 is 100:1
Absolute magnitude:
Equivalent to the apparent
magnitude if star were
placed 10 parsecs (32.6 light
years) from sun.
NATS 1311 From the Cosmos to Earth 13.1.
Figure 13.1
The inverse square
law for light. At
greater distances
from a star, the
same amount of
light passes
through an area
that gets larger
with the square of
the distance. The
amount of light per
unit area therefore
declines with the
square of the
distance.
NATS 1311 From the Cosmos to Earth FIG. 13.8
Figure 13.8
A Hertzsprung-Russell
(H-R) diagram, one of
astronomy's most
important tools, shows
how the surface
temperatures of stars,
plotted along the
horizontal axis, relate
to their luminosities,
plotted along the
vertical axis.
Note - vertical scale is
a logarithmic scale. It
has 11 decades of
range.
NATS 1311 From the Cosmos to Earth FIG. 13.8
Blue supergiants:
Bluest, most luminous,
hottest; moderately
large stars;
low densities and
large masses, very
rare.
Example: Rigel
NATS 1311 From the Cosmos to Earth FIG. 13.8
Red supergiants:
Orange to red in color;
the largest stars and
among the brightest;
large masses
and extremely low
densities; few in
number.
Example: Betelguese
NATS 1311 From the Cosmos to Earth FIG. 13.8
Giants:
Yellow, orange, and red;
considerably larger and
brighter than
the sun;
average to larger than
average masses and low
densities; fairly scarce.
Example: Arcturus
NATS 1311 From the Cosmos to Earth FIG. 13.8
Middle main sequence
stars:
White, yellow, and
orange; stars higher
than the sun on the main
sequence are somewhat
larger, hotter, more
massive, and less dense
than the sun; plentiful in
number.
Example: Sirius
NATS 1311 From the Cosmos to Earth FIG. 13.8
Middle main sequence
stars:
Stars below the sun on
the main sequence are
somewhat smaller,
cooler, fainter, less
massive, and denser
than the sun; plentiful
in number.
Example: Eridani
NATS 1311 From the Cosmos to Earth FIG. 13.8
Figure 13.8
Red dwarfs:
Coolest and reddest
stars on the low rung of
the main sequence;
considerably fainter and
smaller than the sun;
small masses and high
densities; the most
abundant stars.
Example: Barnard's star
NATS 1311 From the Cosmos to Earth FIG. 13.8
White dwarfs:
Mostly white and
yellow; extremely faint
and tiny by solar
standards; enormously
high densities; terminal
evolutionary
development; quite
plentiful.
Example: The binary
companion of Sirius
NATS 1311 From the Cosmos to Earth .
Life Cycle of a Star
1 Protostar
Forms in a solar nebula - A swirling mass of gases
and dust particles
Gravitational collapse causes pressure and
temperature increase.
When temperature reaches 10 million degrees,
hydrogen fusion in the core begins.
Star's position on Hertzsprung-Russell (H-R)
diagram: moves onto the main sequence,
NATS 1311 From the Cosmos to Earth FIG. 14.5
Figure 14.5 The life track of a 1 solar mass star from
protostar to main-sequence star. Time for the Sun to reach
the main sequence is about 50 million years.
NATS 1311 From the Cosmos to Earth .
2. Main Sequence
Location on the main sequence depends on the mass
of the star.
Massive stars lie at the upper left; low mass stars at
the lower right.
O-type stars, more that 8 solar masses, have very high
core temperatures and fuse hydrogen into
helium very rapidly.
Lifetime on main sequence is relatively short millions of years.
NATS 1311 From the Cosmos to Earth FIG. 13.10
Figure 13.10
Along the main
sequence, more
massive stars are
brighter and hotter but
have shorter lifetimes.
(Stellar masses are
given in units of solar
masses: 1 solar mass
equals 2 X 1030 kg.)
Stars on the main
sequence undergo
hydrogen fusion in
their cores.
NATS 1311 From the Cosmos to Earth FIG. 14.6
Figure 14.6
Life tracks from
protostar to the
main sequence
for stars of
different masses.
NATS 1311 From the Cosmos to Earth FIG. 14.8
Figure 14.8
The life track of a 1
solar mass star on an HR diagram from the end
of its main-sequence
life until it becomes a
red giant.
When fusion ceases,
core shrinks and star
expands; becomes a sub
giant. Luminosity
increases and star
becomes a red giant 100
times diameter of
present sun.
For Sun, this takes 1
billion years.
NATS 1311 From the Cosmos to Earth FIG. 14.9
Figure 14.9 After a star ends its main-sequence life, its
inert helium core contracts while hydrogen shell burning
begins. The high rate of fusion in the hydrogen shell forces
the star's upper layers to expand outward.
NATS 1311 From the Cosmos to Earth FIG. 14.10
Figure 14.10
(a)Core structure of a
helium-burning star.
(Triple alpha process)
(b) Approximate
relative sizes of a lowmass star as a mainsequence star, a red
giant, and a heliumburning star. The scale
is not precise; in
particular, the size of
the main-sequence
star is even smaller
compared to the
others.
NATS 1311 From the Cosmos to Earth FIG. 14.11
Figure 14.11
(a)After the helium
flash, the rapid
initiation of the
triple alpha
process,
a low-mass star's
surface shrinks
and heats, so the
star's life track
moves downward
and to the left on
the H-R diagram.
NATS 1311 From the Cosmos to Earth FIG. 14.11
Figure 14.11
(b) This H-R
diagram plots the
luminosity and
surface
temperature of
individual stars in
a cluster, that is,
those stars that
have about the
same luminosity
(i.e., it does not
show life tracks,
just the location of
these stars).
NATS 1311 From the Cosmos to Earth .
3. Red Giant
A star ends its main-sequence life when all the
hydrogen in its core is fused into helium; core
collapses raising its temperature to 100 million
degrees.
Its inert helium core contracts while hydrogen fusion in a
shell outside the core begins. The high rate of
fusion in the hydrogen shell forces the star's
upper layers to expand outward causing the star
to expand greatly in size, moving location on HR diagram up and to the right to the giant
region.
Star becomes a red giant.
NATS 1311 From the Cosmos to Earth .
3. Red Giant
Outer region of star cools.
The core collapses further until the triple alpha process
which converts 3 alpha particles into a carbon
nucleus begins, releasing more energy.
This is a rapid process, called the helium flash,
that causes core collapse to stop.
More massive stars move to the supergiant region.
Triple alpha process continues.
NATS 1311 From the Cosmos to Earth FIG. 14.12
Figure 14.12
The life track of
a 1 solar mass
star from mainsequence star to
white dwarf.
The dashed line
represents the
rapid transition
from planetary
nebulae to white
dwarf as the
ejected outer
layers dissipate,
revealing the
hot core.
NATS 1311 From the Cosmos to Earth .
4. Planetary nebula
When Helium fusion is complete and the core is
carbon, helium fusion moves to the shell outside the
core.
A second expansion occurs.
The star becomes unstable and eventually blows
away all its outer layers,
which are called the planetary nebula,
leaving just the core.
NATS 1311 From the Cosmos to Earth FIG. 14.13
Figure 14.13
Planetary nebulae
occur when lowmass stars in their
final death throes
cast off their outer
layers of gas, as
seen in these
photos. The hot core
that remains ionizes
and energizes the
richly complex
envelope of gas
surrounding it.
(a)Ring Nebula
(b) Helix Nebula
(c) Twin Jet Nebula
NATS 1311 From the Cosmos to Earth .
5. White dwarf
Remaining core of star that is less than 1.4 solar
masses.
Core cools slowly and becomes a black dwarf.
NATS 1311 From the Cosmos to Earth FIG. 14.12
Figure 14.12
The life track of
a 1 solar mass
star from mainsequence star to
white dwarf.
The dashed line
represents the
rapid transition
from planetary
nebulae to white
dwarf as the
ejected outer
layers dissipate,
revealing the
hot core.
NATS 1311 From the Cosmos to Earth .
Stars initially having more than 3 time the solar mass.
Life cycle is similar to that of sun.
Elements beyond carbon formed in core due to extremely high
temperature. Alpha particles fuse with carbon nucleus
to build heavier elements up to iron.
Star eventually becomes unstable and explodes in a supernova
event. During supernova event, elements heavier than
iron are formed.
NATS 1311 From the Cosmos to Earth FIG. 14.14
Figure 14.14 The multiple layers of nuclear burning in the core
of a high-mass star during the final days of its life.
NATS 1311 From the Cosmos to Earth FIG. 14.20
Figure 14.20 Before and after photos of the location of
Supernova 1987A. In the before picture, the arrow indicates
the star that exploded. Note that the supernova actually
appeared as a bright point of light; it appears larger than a
point in the photograph only because of overexposure.
NATS 1311 From the Cosmos to Earth .
Stars initially having more than 3 time the solar mass.
Life cycle is similar to that of sun.
Elements beyond carbon formed in core due to extremely
high temperature. Alpha particles fuse with carbon nucleus
to build heavier elements up to iron.
Star eventually becomes unstable and explodes in a
supernova event. During supernova event, elements
heavier than iron are formed.
Core collapses into neutron star. Electrons are forced into
nucleus to combine with protons to form only neutrons
in nucleus. Extremely dense matter. Mass of the core lies
between 1.4 and 3 solar masses.
NATS 1311 From the Cosmos to Earth FIG. 14.17
Figure 14.17
During the
final,
catastrophic
collapse of a
high-mass
stellar core,
electrons and
protons
combine to
form neutrons,
accompanied
by the release
of neutrinos.
NATS 1311 From the Cosmos to Earth FIG. 15.5
Figure 15.5 (a) A pulsar is a rapidly rotating neutron star that beams
radiation along its magnetic axis. (b) This artwork likens a pulsar (top)
to a lighthouse (bottom). If a pulsar's radiation beams are not aligned
with its rotation axis, they will sweep through space. Each time one of
these beams sweeps across Earth, we see a pulse of radiation.
NATS 1311 From the Cosmos to Earth .
Stars initially having more than 8 time the solar mass.
Stars whose core is more than 8 solar masses collapse into
black holes. No forces are strong enough to stop the
collapse.
Black holes are so massive that nothing, not even light, can
escape from them.
Their escape velocity is greater than the speed of light.
NATS 1311 From the Cosmos to Earth FIG. 14.21
Figure 14.21 Summary of stellar lives. The life stages of a high-mass star
(on the left) and a low-mass star (on the right) are depicted in clockwise
sequences beginning with the protostellar stage in the upper left corner.
NATS 1311 From the Cosmos to Earth .
FORCES IN NATURE:
TYPE
gravity
weakest of all forces,
but dominant in the universe
strong nuclear
strongest force,
but very short ranged
electromagnetic
relatively weak force,
produces electromagnetic radiation
and involved in chemical reactions
weak nuclear
only important in deacy of
elementary particles
NATS 1311 From the Cosmos to Earth .
FUNDAMENTAL PARTICLES
Electrons and neutrinos
Lepton type particles - very light mass elementary
particles
Neutrons and protons
Composed of quarks - heavy elementary particles
6 types of quarks
Up
electric charge
Down electric charge
Strange
Charmed
Top
Bottom
+2/3 e
-1/3e
NATS 1311 From the Cosmos to Earth .
FUNDAMENTAL PARTICLES
Proton - 3 quarks; up, up, down
Electric charge: +2/3, +2/3, -1/3 = 1
Neutron - 3 quarks; up, down, down
Electric charge: +2/3, -1/3, -1/3 = 0