Download Our Sun, Sol - Hobbs High School

Our Sun, Sol, and Stars Like It
Seen in UV light, SOHO EIT
Solar Facts
• The sun is 1.4 million km wide (109 times
Earth’s diameter)
• The sun’s mass is 330,000 times that of
Earth; it accounts for about 99.86% of the
total mass of the Solar System. About ¾ of
the Sun's mass consists of hydrogen, while
the rest is mostly helium. Less than 2%
consists of heavier elements, including
oxygen, carbon, neon, iron, and others.
Solar Facts
• The Sun is neither a solid nor
a gas but is actually a
plasma, a state of matter
made up of charged
particles (protons and
electrons).
• The sun’s layers rotate at
different speeds, with the
photosphere rotating at 251/3 days at the sun’s equator,
34 days at its poles.
Inner Layers of Our Sun
It takes hundreds of thousands of
years for energy from the core to
reach the surface.
• Core—350,000 km,
temperature up to 15.7
million K, pressure of 200
billion atm; nuclear reactor
where hydrogen fusion takes
place
• Radiative zone—650,000
km, temperature decreases
from 7 to 2 million K, photons
of light are emitted,
absorbed, re-emitted at lower
temps
• Convective zone—400,000
km, temp decreases from 2
million to 6000 K, convection
currents move heat to
surface
Nuclear Fusion
• Nuclear fusion is the way that
the sun produces energy. This
reaction converts four hydrogen
nuclei into the nucleus of a
helium atom, releasing a
tremendous amount of energy
and photons.
• During nuclear fusion, energy is
released because some matter
is actually converted to energy.
E = mc2
• Our sun is about halfway
through its expected lifespan of
10 billion years.
Outer Layers of our Sun
• Photosphere—opaque ‘surface’
we see, 500 km thick, has
granules (size of Texas), the tops
of convection cells which give the
photosphere its grainy
appearance, temperature is
5800K
• Chromosphere—10,000 km
above photosphere, 2000 km
thick, red, transparent, hot
incandescent gases with average
temperature of 15,000K.
• Corona—Rarified hot gas
extends millions of km in space,
temp to 2 million K, gas
accelerated by strong magnetic
fields, source of x-rays
Sun’s Magnetic Field
• Our sun has a very
complex and intense
magnetic field, not a
dipole field like Earth’s
• Features that relate to
intense magnetic
activity are sunspots,
solar flares, and solar
prominences.
Sunspots
• Dark spots on the sun’s
surface
• Up to 80,000 km across (5
Earths could fit across)
• Cooler than surrounding areas
(4000 °C) so they appear dark
• Usually occur in pairs, last for
days or weeks
• 11 year cycle in sunspot
maximum
Solar Flare
Solar prominence
CME
• A sudden brightening over the
sun’s surface when material is
heated to tens of millions of
degees. It happens when
magnetic energy stored in the
corona is released as intense
radiation.
• Associated with loops of plasma
called prominences and coronal
mass ejections, huge eruptions of
material into space with the release
of radiation and charged particles.
• Solar storms can cause severe
electrical and communications
blackouts on Earth, affecting air
travel, GPS, etc. The sun’s cycle
was high in 2013 when intense
storms were predicted.
Solar Wind
• Our sun constantly gives off energetic charged particles
that spew outward into space in all directions
• These particles carry the sun’s magnetic field with them
• When the solar wind reaches Earth, it interacts with our
magnetic field to produce auroras in the middle
atmosphere, the ionosphere.
• Jupiter and Saturn also have auroras.
Auroras happen near
both the North and
South magnetic poles.
Lifecycle of Stars Like Our Sun
1.
2.
3.
4.
5.
6.
7.
Protostar
Main sequence star
Red giant
Variable star
Planetary nebula
White dwarf
Black dwarf
Protostar
• A clump of high density gas and/or dust is
held together by gravity
• As more and more gas and dust collects, the
internal pressure rises, and the protostar begins
to heat up and radiate in the infrared.
• When the temperature reaches 10 million
degrees K, hydrogen ‘ignites’ and starts
fusing. Nuclear fusion has begun. A star is
born!
• After hundreds of thousands of years, energy
in the form of light reaches the star’s surface.
As the starlight streams out into space, it pushes
aside any remaining gas and dust.
Main Sequence Stars
• Stars like our sun spend most of their adult
lives on the MAIN SEQUENCE of the
Hertzsprung-Russell diagram, burning
hydrogen and making helium.
• The star has achieved hydrostatic
equilibrium (a balance between inward
gravity and outward gas pressure).
• The time a star spends on the main
sequence depends on its mass: low mass
stars can remain for 100 billion years, a star
like our sun 10 billion, and high mass stars
only a few million years.
So what’s an H-R diagram?
Red Giant Phase
• There comes a time when a star has used
up almost all of the hydrogen in its core.
Nuclear fusion ceases there.
• With no gas pressure to keep it balanced,
the core begins to collapse under gravity’s
influence and gravitational potential energy is
converted to heat. Some of this heat
radiates outward to the outer layers and
increases the rate of hydrogen burning,
expanding the outer layers.
Red Giant Phase (cont.)
• As the outer layers of the star grow
larger, they cool off and become reddish
in color. (A red star is cooler at its surface
than a blue-white star for the same reason
that an iron bar, heated until it is white-hot,
turns red as it cools.)
• We expect our sun to become a red giant
in about 5 billion years, when it will swell
up and become as large as the orbits of
Mars or Jupiter, swallowing the inner
planets.
Meanwhile…back in the star’s core
• The star’s burned-out core continues to collapse
and heat up.
• When the core temperature reaches 100 million K,
helium starts fusing and carbon is produced.
• Again hydrostatic equilibrium occurs. The star
shrinks and moves back onto the Main
Sequence.
• Depending on the star’s mass, it may repeat the
pattern, becoming a red giant two or more times,
each time having its core temperature heating until
it starts fusing in turn carbon, neon, oxygen, and
then silicon. It becomes a VARIABLE STAR,
moving back and forth between the red giant area of
the H-R diagram and the main sequence.
Variable Stars
A Cepheid variable is a star
whose brightness varies
periodically because it
expands and contracts; it
is a type of pulsating star.
A nova is a star that
explosively increases in
brightness. (Pictures 2
months apart)
Stellar Old Age Depends on Mass
• Stars with masses near our Sun’s, when they
have completed helium fusing and have a
carbon core, expand again into a red giant.
• They ‘puff’ off their outer layers which spread
out at 20 to 30 km/s, leaving the core behind.
These layers are illuminated by light from the
star’s core.
• This is called a planetary nebula (named by
William Herschel about 1800; it has nothing to
do with planets!)
• A planetary nebula is visible for 50,000 to
100,000 years, a mere blink in stellar lives.
About 1600 have been observed.
White and Black Dwarfs
• Left behind after the planetary nebula is ‘puffed’
off is the stellar core.
• It continues to collapse into a white dwarf star,
which is extremely hot and dense.
• Our sun’s core will collapse into a white dwarf
about twice the size of Earth with a gravity about
a million times that of Earth.
• This is expected to happen in about 5 billion
years, so don’t panic! Sorry, our sun will NOT
blow up.
• Eventually, the white dwarf will radiate
away all its stored heat and light and
become a corpse—a black dwarf.
A cold cinder… Hypothetical, as
universe isn’t old enough to have black
dwarves.
Stingray Nebula
NGC 2818
NGC 6751
NGC 6543,
Cat's Eye Nebula
NGC 7009,
Saturn Nebula
Low-Mass Stars
• The lives of low mass stars (0.25 mass of our sun) are
relatively unexciting.
• Such a star is small and relatively cool and remains on
the main sequence for 100 billion years until it consumes
all its hydrogen fuel (no outward pressure from burning,
remember) and collapses under its own weight.
• It becomes a white dwarf.
• Eventually, the white dwarf will radiate away all its stored
heat and light and become a corpse—a black dwarf.
Deaths of More Massive Stars
• High-mass stars (4+ our sun) have sufficient
pressure and temperature at their cores to
continue fusing, in turn, helium, carbon,
oxygen, and silicon as the fuel for making
energy, opposing gravity, and keeping the star
(briefly) stable as a variable star. Outer layers
remain of hydrogen, helium, carbon, etc. so
the star is like an onion.
Deaths of More Massive Stars
• Each stage is less efficient, so each new
fusion fuel is used up in a shorter time.
• For a star that is 25 times the mass of our
sun, this would mean:
– Hydrogen fusion lasts 7 million years
– Helium fusion lasts 500,000 years
– Carbon fusion lasts 600 years
– Neon fusion lasts 1 year
– Oxygen fusion lasts 6 months
– Silicon fusion lasts 1 day
Deaths of More Massive Stars
• Eventually, however, the massive star's core
becomes composed of the element iron, which
sets off a final collapse and catastrophe. Why?
Nuclear reactions involving iron do not release
energy.
Death Throes
• When the core of a massive star
collapses, its powerful gravity takes it
right through the white dwarf stage to
produce one of two extremely bizarre
objects—either a neutron star or a black
hole.
• In most cases, the rest of the star then
blows up, in a gargantuan explosion called
a supernova.
SUPERNOVAE
Type Ia
Type II
Supernovae remnants
Neutron Star
• The violent end of a massive star of at least 8
solar masses (with a core of between 1.4 and 3
solar masses) produces so much pressure that
the atoms in the core experience a remarkable
subatomic change: electrons are actually
squeezed into the nuclei and "join" with protons
to become neutrons, creating a neutron star.
• This process also removes all the space within
the atom, leading to a fantastic compression
of the star's remains to about 20 km across.
• One teaspoonful would weigh a billion tons.
Pulsars
• A pulsar (pulsating star)
is a highly magnetized,
spinning neutron star with
jets of particles moving
almost at the speed of
light streaming out
above its magnetic
poles.
• These jets produce very
powerful beams of light.
• The precise periods of
pulsars make them useful
tools to astronomers.
PLM/Pulsars:
Jocelyn Bell
Black Holes
• However, if the star was more than 20 times our
sun’s mass, the result of its supernova explosion
is a completely collapsed object called a black
hole.
• In these objects gravity is so strong that nothing,
not even light, can escape. Space, time, matter,
and energy are all trapped within a tiny
region.
• The event horizon is the boundary where the
inward pull of gravity is so overwhelming that no
information about the black hole's interior can
escape to the outer universe.
Black Holes (cont.)
NGC 4261
Put these in order of lifestage
C
A
B
D
F
G
E
Red giant
H
K
J
K
H, B, J,
K, F, E,
C, A, G,
D
Constellations
• There are 88 named
constellations in the sky
• Constellations are
patterns of stars named
in honor of mythological
creatures or heroes
• Stars in a constellation
are not associated with
each other in any
physical way
Binary Stars
So how do we know how far away stars are?
Stellar parallax is the apparent change in a
star’s position observed when the star is
sighted from opposite sides of Earth’s orbit.
Parallax is used to find distance
Is parallax the only method?
• Astronomers
have LOTS of
ways to
measure
distances
• These methods
overlap so they
‘check’ each
other
FYI Distances to Some Stars
•
•
•
•
•
•
•
•
•
Nearest is Alpha Centauri (binary) @ 4.3 ly
Next is Sirius (binary) @ 8.6 ly
Procyon (binary) @ 11.4 ly
Vega @ 25 ly
Aldebaran @ 67 ly
Mizar (binary binary) @ 78 ly
Antares @ 550 ly
Betelguese @ 570 ly
Rigel @ 860 ly
Apparent and Absolute Magnitude
Some stars’ magnitudes
Star Spectral Class,
Temperature, Mass and Color
Spectral class
Surface Temperature
(K)
Solar mass
(solar mass)
O
> 30,000
> 16
B
10,000-30,000
2.1 - 16
Blue-white to
blue
A
7,500-10,000
1.4 - 2.1
White
F
6,000-7,500
1.04 – 1.4
Yellow to white
G
5,000-6,000
0.8 – 1.04
Yellow
K
3,500-5,000
0.45 – 0.8
Orange
M
<3,500
< 0.45
Apparent color
Blue
Red
Hertzsprung-Russell Diagrams
• A Hertzsprung–Russell diagram shows the
relationship between the luminosity (absolute
magnitude) and temperature of stars.
• H–R diagrams have been helpful in formulating
and testing models of stellar evolution.
• They are also useful for illustrating the changes
that take place in an individual star during its life
span.
• Most stars spend the majority of their lives on
the ‘main sequence’, the diagonal band from
upper left to lower right
Hertzsprung-Russell Diagram
Hyperlink to
animated
star’s
lifecycle.
More H-R diagrams
• You will do a W/S on H-R diagrams, but
before, let’s practice interpreting H-R
diagrams.
http:/www.pbs.org/seeinginthedark/astronomy-topics/lives-ofstars.html