Loading...

PPT – Black Holes PowerPoint presentation | free to download - id: 586e50-ZjgzN

The Adobe Flash plugin is needed to view this content

Black Holes

- The End of Space and Time

Topics

- Introduction
- Black Holes
- Static
- Rotating
- Detection
- Summary

Introduction Gravity (1600s)

All objects fall at the same rate

But how can this be?

Introduction

- 1783
- John Michel, a Cambridge professor, noted that a

sufficiently massive and compact star could have

an escape speed vesc that exceeds that of light,

in which case light would be unable to escape

from it.

Introduction II

- 1907
- Einstein had a crucial insight
- A person falling off a building experiences no

gravity! - The happiest thought of my life

Introduction III

- This insight led Einstein to propose the
- Principle of Equivalence
- A local frame of reference (for example, the

inside of a small elevator) in free fall is

indistinguishable from a local frame of reference

in free space.

Introduction IV

Principle of Equivalence

Introduction V

- Einstein's great leap of imagination
- He suggested that objects in a gravitational

field move as they do, not because of a

mysterious force called the force of gravity,

but, because the space and time in which they

move is warped by the presence of matter and

energy. - Consequently, objects of differing mass fall

towards the ground with the same acceleration

because they follow the same space-time

contours.

Gravity as Curved Spacetime

- Spacetime
- Is warped by matter and energy
- All objects
- Experience the same hills and valleys of

spacetime.

Introduction General Relativity (1915)

Bending of star-light by the Sun

Sir Arthur Eddington Eclipse Expeditions 1919

The Schwarzschild Solution (1916)

- Karl Schwarzschild
- Karl Schwarzschild found the first exact solution

of Einstein's equations. - It describes the space-time geometry around any

spherical object.

http//scienceworld.wolfram.com/biography/photo-cr

edits.htmlSchwarzschild

Static Black Holes

Photon sphere

Event horizon

Escape speed light speed

3RS/2

RS

RS is called the Schwarzschild Radius RS 3 km

for the Sun

Singularity A boundary in space and time

Time-Warps Near the Event Horizon

- Time-Warps
- The event horizon is a one-way boundary You can

enter, but in the words of a famous song, You

can check out anytime you like but you can never

leave - Moreover, from the viewpoint of a traveler who

crosses the event horizon the crossing occurs in

a finite amount of time. - But from the viewpoint of someone far from the

black hole, the traveler takes an infinite amount

of time to cross!

Space-Warps Near the Event Horizon

- Rotating Black Holes
- Black holes have two
- special boundaries
- Event Horizon
- Stationary Limit
- For static holes these boundaries coincide, but
- differ for holes that rotate.

Fig. 14-7, p.284

Detecting Black Holes Or how to find the grin

of the Cheshire cat

Fig. 14-8, p.285

The Grin of Cygnus X-1

Fig. 14-10a, p.286

Fig. 14-11, p.288

Super-Massive Black Holes

Galaxy M87 Distance 50 million ly Length of

jet 4000 ly MassBH 2 billion M? RadiusBH 3km

x 2 billion 6 billion km 40 AU

Summary

- The finite speed of light allows, in principle,

the existence of objects from which light cannot

escape. - In Einsteins theory of gravity the latter is

explained as a warping of space and time of which

black holes are the extreme examples. - Evidence is mounting suggesting, amazingly, that

such objects actually exist.