Read: S2, S3, Chap 18 10/30/14 – slide 1

A100–Exploring the Universe: Black holes

Martin D. Weinberg

UMass Astronomy

weinberg@astro.umass.edu

October 30, 2014

Announcements

⊲ Announcements Forming BHs

Energy

Escape velocity

Schwarzschild

Sizes of black holes

Thought question

Laws of physics

Special Relativity

Consequences

Photon clock

More consequences

General Relativity

Back to Black holes

Event horizon

Gravity around a black hole

Gravitational redshift

Not really Black!

Evaporating Holes

Other Predictions

Read: S2, S3, Chap 18 10/30/14 – slide 2

The solar neighborhood visualized!

http://stars.chromeexperiments.com

Thanks to Raymond Phoung

http://stars.chromeexperiments.com http://stars.chromeexperiments.com

Announcements

⊲ Announcements Forming BHs

Energy

Escape velocity

Schwarzschild

Sizes of black holes

Thought question

Laws of physics

Special Relativity

Consequences

Photon clock

More consequences

General Relativity

Back to Black holes

Event horizon

Gravity around a black hole

Gravitational redshift

Not really Black!

Evaporating Holes

Other Predictions

Read: S2, S3, Chap 18 10/30/14 – slide 2

The solar neighborhood visualized!

http://stars.chromeexperiments.com

Thanks to Raymond Phoung

Exam #2: November 04

⊲ Covers Chaps: S4, 14, 15, (16), 17, 18

http://stars.chromeexperiments.com http://stars.chromeexperiments.com

Announcements

⊲ Announcements Forming BHs

Energy

Escape velocity

Schwarzschild

Sizes of black holes

Thought question

Laws of physics

Special Relativity

Consequences

Photon clock

More consequences

General Relativity

Back to Black holes

Event horizon

Gravity around a black hole

Gravitational redshift

Not really Black!

Evaporating Holes

Other Predictions

Read: S2, S3, Chap 18 10/30/14 – slide 2

The solar neighborhood visualized!

http://stars.chromeexperiments.com

Thanks to Raymond Phoung

Exam #2: November 04

⊲ Covers Chaps: S4, 14, 15, (16), 17, 18

Today

1. Black holes

⊲ What they are

⊲ What they are NOT

⊲ Theories of relativity

http://stars.chromeexperiments.com http://stars.chromeexperiments.com

Announcements

⊲ Announcements Forming BHs

Energy

Escape velocity

Schwarzschild

Sizes of black holes

Thought question

Laws of physics

Special Relativity

Consequences

Photon clock

More consequences

General Relativity

Back to Black holes

Event horizon

Gravity around a black hole

Gravitational redshift

Not really Black!

Evaporating Holes

Other Predictions

Read: S2, S3, Chap 18 10/30/14 – slide 2

The solar neighborhood visualized!

http://stars.chromeexperiments.com

Thanks to Raymond Phoung

Exam #2: November 04

⊲ Covers Chaps: S4, 14, 15, (16), 17, 18

Today

1. Black holes

⊲ What they are

⊲ What they are NOT

⊲ Theories of relativity

Questions?

http://stars.chromeexperiments.com http://stars.chromeexperiments.com

Stellar evolution ⇒ Black Holes

Announcements

⊲ Forming BHs Energy

Escape velocity

Schwarzschild

Sizes of black holes

Thought question

Laws of physics

Special Relativity

Consequences

Photon clock

More consequences

General Relativity

Back to Black holes

Event horizon

Gravity around a black hole

Gravitational redshift

Not really Black!

Evaporating Holes

Other Predictions

Read: S2, S3, Chap 18 10/30/14 – slide 3

A star with M > 18MSun would leave behind an iron core more massive than 2-3 MSun

Neutron degeneracy pressure would fail with nothing to

stop its gravitational collapse

Core would collapse into a singularity!

Gravity becomes so strong that nothing, not even light,

can escape

Infalling matter is shredded by powerful tides

Black hole!

⊲ Black because they neither emit nor reflect light

⊲ Hole because nothing entering can ever escape

Energy is conserved: a quick review

Announcements

Forming BHs

⊲ Energy Escape velocity

Schwarzschild

Sizes of black holes

Thought question

Laws of physics

Special Relativity

Consequences

Photon clock

More consequences

General Relativity

Back to Black holes

Event horizon

Gravity around a black hole

Gravitational redshift

Not really Black!

Evaporating Holes

Other Predictions

Read: S2, S3, Chap 18 10/30/14 – slide 4

Definition:

Energy is the capacity of a physical system to do work

Definition:

Work is application of force over a distance

Kinetic energy

Announcements

Forming BHs

⊲ Energy Escape velocity

Schwarzschild

Sizes of black holes

Thought question

Laws of physics

Special Relativity

Consequences

Photon clock

More consequences

General Relativity

Back to Black holes

Event horizon

Gravity around a black hole

Gravitational redshift

Not really Black!

Evaporating Holes

Other Predictions

Read: S2, S3, Chap 18 10/30/14 – slide 5

Example: kinetic energy from accelerating an object

fv=v

v=0

d

d

m

m

⊲ Push object with constant force over distance d

⊲ Final velocity vf

⊲ Average velocity: v̄ = vf 2

= d

t

⊲ Force required: F = ma = m vf t

⊲ Work done (energy): E = Fd = mvfd

t =

1

2 mv2f

Kinetic energy

Announcements

Forming BHs

⊲ Energy Escape velocity

Schwarzschild

Sizes of black holes

Thought question

Laws of physics

Special Relativity

Consequences

Photon clock

More consequences

General Relativity

Back to Black holes

Event horizon

Gravity around a black hole

Gravitational redshift

Not really Black!

Evaporating Holes

Other Predictions

Read: S2, S3, Chap 18 10/30/14 – slide 5

Example: kinetic energy from accelerating an object

fv=v

v=0

d

d

m

m

⊲ Push object with constant force over distance d

⊲ Final velocity vf

⊲ Average velocity: v̄ = vf 2

= d

t

⊲ Force required: F = ma = m vf t

⊲ Work done (energy): E = Fd = mvfd

t =

1

2 mv2f

Kinetic energy

Announcements

Forming BHs

⊲ Energy Escape velocity

Schwarzschild

Sizes of black holes

Thought question

Laws of physics

Special Relativity

Consequences

Photon clock

More consequences

General Relativity

Back to Black holes

Event horizon

Gravity around a black hole

Gravitational redshift

Not really Black!

Evaporating Holes

Other Predictions

Read: S2, S3, Chap 18 10/30/14 – slide 5

Example: kinetic energy from accelerating an object

fv=v

v=0

d

d

m

m

⊲ Push object with constant force over distance d

⊲ Final velocity vf

⊲ Average velocity: v̄ = vf 2

= d

t

⊲ Force required: F = ma = m vf t

⊲ Work done (energy): E = Fd = mvfd

t =

1

2 mv2f

Kinetic energy

Announcements

Forming BHs

⊲ Energy Escape velocity

Schwarzschild

Sizes of black holes

Thought question

Laws of physics

Special Relativity

Consequences

Photon clock

More consequences

General Relativity

Back to Black holes

Event horizon

Gravity around a black hole

Gravitational redshift

Not really Black!

Evaporating Holes

Other Predictions

Read: S2, S3, Chap 18 10/30/14 – slide 5

Example: kinetic energy from accelerating an object

fv=v

v=0

d

d

m

m

⊲ Push object with constant force over distance d

⊲ Final velocity vf

⊲ Average velocity: v̄ = vf 2

= d

t

⊲ Force required: F = ma = m vf t

⊲ Work done (energy): E = Fd = mvfd

t =

1

2 mv2f

Potential energy

Read: S2, S3, Chap 18 10/30/14 – slide 6

Example: potential energy is energy that can be converted to kinetic

energy by moving in a force field

Ground level

v=0

v=vf

⊲ Potential energy is p