Transcript No Slide Title

Today’s Comments


Graded papers – see Raquel to get old papers or tests.
Tests



Lab Students: Lab Exam today, Apr. 16
D2L Quiz 10 available
Observations



Binoculars available for Moon Craters on your own. Fill out loan form.
Sunset Part 2. Work on this. Due Apr. 28
Telescopes, Star Gazing & Moon Craters available at UMN,
Macalester and Eagle Lake Observatory – see dates on calendar

Space Exhibit at Science Museum of MN on 5:30-9pm, Thursday, May
7; Evite invitation coming tomorrow and you need to RSVP
 Answer EVITE – if you didn’t get this, see Raquel
3M & STEM free lunch with 3M Speaker, T3850, 12-1pm, Apr. 17


Apr. 16, 17, 19, 24, 25, 28 & May 1
Black Holes
What is a black hole?
 Special Theory of Relativity
 General Theory of Relativity
 What is gravity? How can it effect light?
 How to make a black hole
 Structure (Singularity and Event Horizon)
 How to find a black hole

What is a Black Hole?
What is a Black Hole?

A black hole is a mass condensed so
tightly that nothing, not even light, can
escape from it’s gravitational effects.
Collapsed mass > 3 M
 Nothing can escape

How can that be?
Mass of the star determines its fate
mass < 1.4 M
1.4 M < mass < 3 M
Possibly 3 to 8 M
mass > 3 M
Always for > 8 M
Know This and the
End of Life State
SPEED
LIMIT
300 000 km/s
Special Theory of Relativity
Nothing
It’s not
just the limit,
in the
universe
it’s the law!
can travel faster
than the
speed of light
SPEED
LIMIT
Special Theory of Relativity
(Special Relativity, SR)
300 000 km/s
Tested many times
in many ways.
http://www.exphy.uni-duesseldorf.de/ResearchInst/FundPhys.html
http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html
Newton’s
Gravity
Law of Universal Gravitation
• Every mass attracts every other mass.
• Bigger masses  bigger force
• Bigger separation  smaller force
I. Newton
D
M
m
F
F
F G
mM
D
2
VLaunch=0
Launch Speed
VLaunch
VLaunch
VLaunch
VLaunch
VLaunch
VLaunch
V esc 
2 GM
D
Escape Speed
V esc 
2 GM
r
V esc 
2 GM
D
Earth
Vesc= ~ 10 km/s
Escape Speed
V esc 
2 GM
r
SUN
Vesc= ~ 600 km/s
Escape Speed
r ~ Moon size
V esc 
2 GM
r
Vesc= ~ 15 000 km/s
3 M
Escape Speed
V esc 
2 – 3 MILES
3 M
2 GM
r
Vesc= 300 000 km/s
Speed
300 000 km/s
Limit
Nothing Escapes…. Not even light!
How can you crush 3 M into 2-3 miles?
Big Supernovas (hypernovas)
Hypernova – explosion from very massive star
collapsing into a black hole
Mass of the star determines its fate
mass < 1.4 M
mass < 3 M
Possibly 3 to 8 M
mass > 3 M
Always for > 8 M
Know This and the
End of Life State
Mass of the star determines its fate
Supernova Ia after
white dwarf explodes
Supernova II
creates neutron star
Hypernova
creates black hole
How can you crush 3 M into 2-3 miles?
Hypernovas
or
Lots of gas
condensing
http://antwrp.gsfc.nasa.gov/apod/ap050402.html
Why doesn’t light escape from a
black hole?
(or how can gravity pull on light?)
General Theory of Relativity
Gravity
is
General Theory of Relativity
Gravity is the curvature of space-time
This is why masses attract!
Mass deforms space-time.
Sheet demo
http://einstein.stanford.edu/content/education/EducatorsGuide/Page7.html
A second mass simply follows
the curvature of space-time.
Coin wishing well demo
http://einstein.stanford.edu/content/education/EducatorsGuide/Page7.html
Both mass and light
follow the curvature
of space-time.
Space is something!
Light travels at 300 000 km/s in it.
Masses warp it.
Has General Relativity been tested?
Many times – all positive
Tests of General Relativity
• Mercury’s orbit
precession
• Light bent by gravity
– Eclipse in 1919
Tests of General Relativity
• Mercury’s orbit precession
• Light bent by gravity
– Eclipse in 1919
– Gravitational lensing - focusing of light from distant
galaxy or quasar by an intervening galaxy; produces
multiple images
– Quasar – energetic black hole core of a distant galaxy
Einstein’s Cross
quasar behind the center of a massive galaxy and displayed as a clover leaf
http://apod.nasa.gov/apod/ap130102.html
Tests of General Relativity
• Mercury’s orbit precession
• Light bent by gravity
– Eclipse in 1919
– Gravitational lensing - focusing of light from
distant galaxy or quasar by an intervening galaxy;
produces multiple images
– Quasar – energetic core of a distant galaxy
• Gravitational redshift
– Lengthening of photon wavelength due to leaving
a gravity field
Modern Examples of General Relativity –
Continual Evidence
• Gravity Probe A (1976)
• Radio waves sent to Viking, Mars
lander (1979)
• Radio waves sent to Cassini, Saturn
orbiting spacecraft, on other side of
Sun (2003)
Cassini verifies
General Relativity
(space-time is curved).
Einstein’s equations
work!
Modern Examples of General Relativity –
Continual Evidence
• Gravity Probe A (1976)
• Radio waves sent to Viking, Mars
lander (1979)
• Radio waves sent to Cassini, Saturn
orbiting spacecraft, on other side of
Sun (2003)
• Gravity Probe B, in Earth orbit (2011)
Gravity Probe B
verifies General
Relativity
(space-time is
curved and
twisted).
Einstein’s
equations work!
What
happens
inside a
black
hole?
As masses get closer,
gravity gets stronger!
So the tighter you cram in mass,
the stronger gravity gets!
Once 3 M is crammed into
2-3 miles, no known force
can stop further collapse.
All the mass collapses into a
point of zero size called the
singularity!
Singularity
A word about
General Relativity
Weak field case
Strong field case
And Einstein’s
equations
Singularity? All the mass is in 0 size?
Signal that our theories need some
modification.
Quantum Gravity?
What is the structure of a Black Hole?
Singularity
Event
Horizon
All mass
condensed here
Limit!!!!!!!
0 size?
Inside here
Infinite density?
Escape speed >
speed of light
How massive are black holes?
• 1. Stellar mass
(3-20 M )
• 2. Mid-mass
(100-10 000 M )
• 3. Massive
(Millions M )
If a black hole is black,
how do you “see” one?
1. Binary “stars”
Star and black hole orbiting each other.
Look for wobble in the spectral lines of a
visible star.
http://www.unm.edu/~astro1/101lab/lab9/lab9_C1.html
Example - Cygnus X-1
Super Blue Giant Wobble of spectral lines
Indicate an unseen
companion ~ 9M
Source: http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html
If a black hole is black,
how do you “see” one?
2. Accretion Disk
Gas orbiting just outside the event horizon
a. See X-Rays or UV from colliding matter
b. See accretion disk
Cygnus X-1
Dark companion ~9 M
Strong X-ray source
Source: http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html
Bloated
star
Black Hole
Accretion
Disk
http://antwrp.gsfc.nasa.gov/apod/ap080811.html
NGC 4261
X-rays!!!
Optical Image
http://chandra.harvard.edu/photo/2003/ngc4261/ngc4261_scale.jpg
http://www.nasa.gov/centers/goddard/news/topstory/2004/0720donutcloud.html
If a black hole is black,
how do you “see” one?
3. Jets
Perpendicular to accretion disk
http://apod.nasa.gov/apod/ap130312.html
http://www.nasa.gov/centers/goddard/images/content/96922main_ngc426
1_hubble_m.jpg
X-Rays from radio jets in NGC4696
Composite Image Credit: X-ray in red - NASA/ CXC/S.Allen (Kavli Inst., Stanford) et al.;
Radio in blue - NRAO/G.Taylor (VLA); Infrared in green - NASA/ESA/W.Harris (McMaster Univ.)
http://antwrp.gsfc.nasa.gov/apod/ap060427.html
M87
center
Centaurus A
http://heasarc.gsfc.nasa.gov/docs/cgro/images/epo/gallery/agns/index.html
Centaurus A
Colour composite image of Centaurus A, revealing the lobes and jets emanating from the active galaxy’s central black hole.
Image: ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray).
Hercules A. Image Credit: NASA, ESA, S. Baum & C. O'Dea (RIT), R. Perley and W. Cotton
(NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA)
If a black hole is black,
how do you “see” one?
4. Gas, dust swirling around black hole
(much further out than the accretion disk)
– Doppler Effect to measure speed
– Kepler’s Laws to calculate mass
~100 000 ly
~100 billion stars
Sombrero Galaxy
Inner 2000 LY
contains
1 billion M
Andromeda Galaxy
Inner 10 LY
contains
20 million M
Milky Way
Toward
Sagittarius
Swirling gasses imply
~3 million M at center
If a black hole is black,
how do you “see” one?
5. Star near center of Milky Way
– Doppler and Kepler
Video clip of S2 orbit around a black hole at Milky Way
center:
http://www.youtube.com/watch?v=u_gggKHvfGw
Article here:
http://www.eso.org/public/usa/news/eso0226/
Star S2 near central black hole in Milky Way
S2 orbit is 15 years at
5000 km/s
Implies central black hole
of 3.7 million M
If a black hole is black,
how do you “see” one?
6. Binary black
holes
merging
Animation here:
http://chandra.harvard.edu/ph
oto/2006/a400/animati
ons.html
25 000 ly separation
1200 km/s through gas
http://antwrp.gsfc.nasa.gov/apod/ap060412.html
If a black hole is black,
how do you “see” one?
7. Clumps of hot iron
gas orbit at 30 000
km/s ( 1/10 c)
Credits: NASA/Dana Berry, SkyWorks Digital
http://spaceflightnow.com/news/n0501/10speedracing/
If a black hole is black,
how do you “see” one?
8. Star ripped apart
by black hole
Source:
http://chandra.harvard.edu/
photo/2004/rxj1242/
If a black hole is black,
how do you “see” one?
9.
UltraLuminous
X-Ray
sources
If a black hole is black,
how do you “see” one?
10.
Space-time
Dragging
(twisting)
Ways to Detect Black Holes
1. Binary stars
2. Accretion disk
3. Jets
4. Gas, dust swirling well outside black hole
5. Star near center of Milky Way
6. Binary black holes merging
7. Clumps of hot iron gas in orbit
8. Star ripped apart by black hole
9. Ultra-luminous x-ray sources
10. Space-time dragging
Next Week
Tuesday: Star Groups, Galaxies and
Groups of Galaxies
 Thursday: Galaxy Motion & Hubble’s Law
