Transcript Science Olympiad - Department of Physics and Astronomy

Science Olympiad
Astronomy C 2007
Joshua Haislip
Stellar Nurseries
Shockwaves from distant supernovae or
gravity from nearby stars can trigger
collapse.
Consists of dense regions of molecular
hydrogen
around 3.5 light years
Pillars are left after ‘erosion’ from the
intense ultraviolet radiation of nearby,
bright stars
Evaporating Gaseous Globules
Protostars and
Protoplanetary Disks
As gas collapses it heats up
15 times
Neptune’s orbit
Before nuclear fusion and
hydrostatic equilibrium is
achieved, this ball of gas is
known as a protostar
The disk of swirling dust and
gas orbiting this protostar/star
is called the protoplanetary
disk
T Tauri Star
Forming
System
NICMOS Peers Through Dust to
Reveal Young Stellar Disks. A
View of IRAS 04302+2247
Brown Dwarfs
Were not big enough to ignite
nuclear fusion
Turbulent stellar duds
Less that 3% mass of sun
TWA 5B
Red Dwarfs
Slow rate fusion of hydrogen into
helium in core
Between 8% and 50% the mass of
the sun
Most common type of star in the
galaxy
Turbulent interiors
Proxima Centauri:
closest star to the sun
White Dwarf
As red dwarf stars use up all of
their fuel in the core, they cool
down
This allows for collapse -> they
shrink to about the size of the Earth
Process takes longer than the age
of the Universe -> we have never
this type of white dwarf
Sun-like Star
Currently 70% hydrogen, 28%
helium, and 2% other metals
Fusion of hydrogen into helium is
taking place in core
700 million tons of hydrogen are
converted to helium each second
Red Giant
When solar-type stars run out of
hydrogen in the core, they cool and
begin to collapse
Collapsing causes temperature to
rise, igniting a shell of hydrogen
around the core
Star expands over 100 times its
original size, core collapses further
igniting helium fusion
The surface of our sun might
swallow the Earth when it becomes
a red giant
Planetary Nebula
After helium is depleted in core,
star blows off outer layers leaving
behind hotter star
High speed stellar winds from the
new hot star slam into previously
ejected material creating the nebula
White Dwarf
The core will eventually collapse to
a white dwarf
Type Ia Supernova
Chandrasekhar limit:
A white dwarf with more than 1.4
solar masses will collapse
A white dwarf stripping material off
a binary companion could result in
breaking this limit
Type Ia Supernova will result
Tycho Brahe
Blue Supergiant
Extremely massive stars with tremendous
power output
20 times the diameter and 30 times the mass of
the sun
If we replace the sun with Rigel
(blue supergiant in Orion) this is
what would be seen from earth
The sun as it appears from earth
(compare with Rigel image to the left)
Red Giant
When blue supergiants run out of
hydrogen in the core, they cool and
begin to collapse
Collapsing causes temperature to
rise, igniting a shell of hydrogen
around the core
Star expands over 100 times its
original size, core collapses further
igniting helium fusion
The surface of our sun might
swallow the Earth when it becomes
a red giant
Same as with solar-type stars
Blue Giant
Unlike solar-type stars, as massive
stars expand to red giants their
outer layers are ejected leaving a
blue giant, or Wolf Rayet star
Similar to planetary nebulas, the
new blue giant’s hot solar winds
collide with previously ejected
material creating nebulae
Crescent Nebula
Type II Supernovae
When a massive star runs out of fuel, it will
collapse to either a neutron star or a black hole
Energy released during the collapse blows the
star apart
Neutron Star
Only around 12 miles in diameter
Extremely dense! 1 spoonful of neutron star
material would weigh over 10 billion tons
Some act as rapidly rotating lighthouses
beaming radiation (puslars or Little Green Men)
Blue Supergiant
Some blue supergiants are so
large, they completely skip the
red giant phase
Eta Carina (depicted to the right)
is around 100 times the mass of
our sun and produces energy at
a rate which if 5 million times that
of the sun
Type II Supernovae
When a massive star runs out of
fuel, it will collapse to either a
neutron star or a black hole
Energy released during the collapse
blows the star
Cataclysmic variable
Same as with Blue Giant star
Black Hole
The densest objects in the universe
When very massive stars collapse,
nothing can stop them
All mass is compressed to a single
point in space
Blue Supergiant
Most massive of all stars (around 150
solar masses)
Violently unstable due to the amount
of radiation they produce
HD 5980
Black Hole
The densest objects in the universe
When very massive stars collapse,
nothing can stop them
All mass is compressed to a single
point in space
Hertzsprung Russell Diagram
Hertzsprung Russell Diagram
Hertzsprung Russell Diagram – M55
Magnitude
Astronomers measure the brightness of stars in magnitudes. In this
magnitude scale, the higher the number, the fainter the object.
There are two types of magnitudes:
Apparent: magnitude of the star determined by how bright it appears
from the earth
Absolute: magnitude of the star determined by how bright it appears
from 10 parsec away
While it is easy to determine the apparent magnitude, astronomers are
always looking for new ways to determine a stars absolute magnitude.
Intrinsic Variable Stars
Excellent way of determining distances
because astronomers have found a
relationship between period and luminosity
or absolute magnitude.
This absolute magnitude can be calculated
as a function of the variable’s period.
Comparing this to its apparent magnitude
one can calculate the distance with the
distance modulus equation.
Two main types:
RR Lyrae
Cepheid Variable
RR Lyrae Stars
Population II stars (old, red
stars and other objects
found in the galactic halo
and galactic bulge of a
spiral galaxy
Found in halos of galaxies
-> globular clusters
Periods are usually <1 day
Cepheid Variables
Found in spiral arms
Periods are usually much
longer than RR Lyrae stars
(from 5-75 days)
Period of pulsation is
directly related to its
luminosity: the longer the
period, the greater the
mean intrinsic brightness
Extrinsic Variables
Eclipsing Binary
Binary star system in which the
components periodically pass in
front of one another as seen from
Earth.
Three types:
Algol Star – constant/near constant
brightness between minima
W Ursae Majoris – continuous light
variation, no clear start/stop to
eclipse
Beta Lyrae – brightness changes
are fairly smooth and continuous
d
m

M

5
Log
(
)
The Distance Modulus:
10
10 pc
d  100.2( m M 5)  10.2  1
Kepler’s 3rd Law with Newtons addition:
where:
T = planet's sidereal period
r = radius of the planet's circular orbit
G = the gravitational constant = 6.67*10
M = mass of the sun
11
2
4

T2 
r3
GM
m3
kg * s 2
1 pc = 206,265 au = 3.26 ly = 3.08 x 10^16m
1° = 60 arcmin = 60´ ; 1´ = 60 arcsec = 60˝
Inverse Square Law: L = 1/r^2
Circumference, Area, Surface Area, and Volume of a Sphere
Most Importantly: Get the students excited about astronomy!
Wikipedia
Use Wikipedia to search for more information about variable stars and
stellar evolution
www.wikipedia.org
Stellarium
Free virtual planetarium! See the sky as it looks at any time in the future or
past from any place on Earth. Also zoom in on planets and Messier objects
to see them as they would look through a telescope.
http://www.stellarium.org/
Test your students’ Stellarium skills with my “Stellarium Challenge”
Test your students’ understanding of Kepler’s third law, as well as the weight
equation with my lab “Measuring the Mass of Jupiter”: