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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  Apr. 16, 17, 19, 24, 25, 28 & May 1  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

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 in the universe

it’s the law!

can travel faster than the speed of light

SPEED LIMIT 300 000 km/s

Special Theory of Relativity (Special Relativity, SR) 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

V

Launch V

Launch

V Launch =0

Launch Speed

V Launch

V

Launch V Launch

V Launch

V esc

2

GM V esc

 2

GM D

Escape Speed

V

esc

 2

GM r

Earth V esc = ~ 10 km/s

SUN

Escape Speed

V

esc

 2

GM r

V esc = ~ 600 km/s

r ~ Moon size

Escape Speed

V

esc

 2

GM r

V esc = ~ 15 000 km/s

3 M



Escape Speed

V

esc

 2 – 3 MILES 2

GM r

3 M  V esc

= 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 0 size?

Infinite density?

Limit!!!!!!!

Inside here 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 ~ 9

M

 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

Sombrero Galaxy

~100 billion stars

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. Ultra Luminous 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