Transcript 2009_02_02 LP07 Death and Black Holes

Astronomy 100
Death and Black Holes
(Two things you can’t escape?)
Quiz Today!
• You have until 6:40 to complete 3 questions.
• WRITE NEATLY! PLEASE, I’m begging you!
We Grow Accustomed to the Dark
We grow accustomed to the Dark—
When light is put away—
As when the Neighbor holds the
Lamp
To witness her Goodbye—
The Bravest—grope a little—
And sometimes hit a Tree
Directly in the Forehead—
But as they learn to see—
A Moment—We uncertain step
For newness of the night—
Then—fit our Vision to the Dark—
And meet the Road—erect—
Either the Darkness alters—
Or something in the sight
Adjusts itself to Midnight—
And Life steps almost straight.
And so of larger—Darkness—
Those Evenings of the Brain—
When not a Moon disclose a sign—
Or Star—come out—within—
Emily Dickinson
• Answer Now: What do you know about black
holes? Draw me a picture of one.
• Goal:
– Understand special types of stars and star death
– Know why stellar clusters are important for
learning about star life cycles
• Vocabulary: Mass-luminosity relationship, Helium
flash, degenerate matter, Chandrasekhar limit,
Lagrangian point, Roche lobes, SN II, SN Ia, SN Ib,
neutrinos, neutron star, pulsar, escape velocity,
singularity, Schwarzschild radius, time dilation,
spaghettification, gamma ray bursts, black hole
Planck Curve
(Color-Temp Relationship)
• There is a relationship between peak
wavelength and temperature
• http://www4.nau.edu/
Mass-Luminosity Relationship
• We also have a
relationship
between MASS and
Luminosity
• http://csep10.phys.utk.edu/astr
162/lect/binaries/masslum.html
Things you can tell from spectra
(so far)
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Color
Composition
Motion (red shift)
Rotation (red shift)
Temperature
Luminosity
Mass
Color
• Star type (O, B, A, F, G,
K, M)
• Star luminosity class (we
didn’t really go into this –
but it tells you regular star,
dwarf, giant, or supergiant)
• ?
• ?
• ?
Stellar Cluster Evolution
• Stars in a cluster were born at the same time
• They often have very similar composition
• So differences are because of their mass
• Snapshot of one “age” of a bunch of similar
stars
• Degenerate Matter
–
http://www.istockphoto.com/file_closeup/architecture-and-buildings/5515080-bridge-over-highway-night-timelapse.php?id=5515080
• Helium Flash
Chandrasekhar Limit
• If what is left after a star begins to die is:
Greater than 1.4 solar masses  neutron star
Less than 1.4 solar masses  white dwarf
Life Expectancy
• Giant stars – burn fast – die young
– 10s of millions of years
• Medium stars – burn – die middle-aged
– 10s of billions of years
• Tiny stars – burn “like forever” – die ANCIENT
– Well, the universe has only been around 14 billion
years, so no white dwarfs have really died yet.
Death from the Skies
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Mass is related to weight.
Weight is what we call mass on EARTH
Mass is “how much stuff”
Weight is “how much” that “stuff” weighs on
EARTH.
• I have to use mass now, but if that’s confusing,
say “weight” in your head.
Lagrangian Points!!
http://history.nasa.gov
Gravity
More massive
objects pull
more strongly
Closer objects pull
more strongly
Roche Lobes
• What happens to
the Sun as it dies?
Gravity
More massive
objects pull more
strongly
Closer objects pull
more strongly
http://personal.tcu.edu/~pmarcum/courses/P2083/handouts/images/roche.jpg
Supernovae (plural of Supernova)
• Supernova II
– What we talked about last week:
– collapseexplode
• Supernova Ia
– White dwarf gains mass, collapseexplodes
– Roche lobes
• Supernova Ib (less important)
– Regular supernova, but happens to a star with no
outer layer.
Neutrinos
• When SN 1987a exploded we detected a huge
flood of neutrinos 4 hours before we detected
the light. How is
that possible?
• Cross-section
• Detectors
Super Kamiokande: http://www.aip.org/png/images/deth20.jpg
Neutron Star
• 8-20 Solar masses
• Smaller – generally does Sun-like collapse
• Bigger – ends up with a black hole
Pulsars
(a special type of Neutron Star)
•
http://www.youtube.com/watch?v=duh2srW8j3U
• Jocelyn Bell Burnell
• Highly magnetized
• New research:
– Alice Harding
– Roger Romani
Black Holes
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escape velocity
singularity
Schwarzschild radius
Time dilation (relativity)
Spaghettification
Getting energy out of a black hole (how do we
detect them then?)
• http://www.squidoo.com/latestinventions
WAYS TO DIE
• http://www.youtube.com/watch?v=h1iJXOUM
Jpg
• http://fora.tv/2008/02/19/Neil_DeGrasse_Tys
on_Death_by_Black_Hole
Gamma Ray Bursts
• Gamma-ray bursts are the universe's most luminous
explosions. Most occur when massive stars run out of nuclear
fuel. As a star's core collapses, it creates a black hole or
neutron star that, through processes not fully understood,
drive powerful gas jets outward. These jets punch through the
collapsing star. As the jets shoot into space, they strike gas
previously shed by the star and heat it. That generates bright
afterglows.
Sketch, Write, Answer
I’m doing this so that I know if I’m effective as a teacher. This helps me be sure if I
should review something or move on. Please answer these questions in any
way you prefer. If you’d like to be verbal, come chat with me quietly.
– How do we detect black holes if light cannot escape?
– Why can’t degenerate matter heat up normally?
– If 8 million billion quadrillion (a lot) of neutrinos hit
you RIGHT NOW, would you feel it? Would you get
cancer later in life?
– What is the ONE factor that determines how a star
will live its life and die?