Flamsteed Astronomy Society

Black Holes and White Rabbits

Star Lecture — March 14, 2005

Professor John Campbell Brown, Astronomer Royal for Scotland


“You will notice that during this performance my hands never leave my arms”.    When he was 10 years old John Brown was given a magic set, Sputnik was launched, and Patrick Moore started his programmes on TV.  Ever since, John seems to have developed a parallel ‘stealth career’ combining these loves of his life into Magi-science or ‘Astracadabra’, as a memorable way of illustrating science:  

To John there’s nothing odd about this marriage of interests—Astronomy is unreachable by definition, and likewise, you can’t poke about behind the magician’s table looking for the wires.  John uses fascinating magic to demonstrate a whole range of astronomical mind benders.   For “Black Holes & White Rabbits” he concedes the title came before the content, but the medium is entirely appropriate..  throw a ball into the air and it falls to Earth ... unless you throw it fast enough to escape Earth’s gravity—the “escape velocity”, in which case it don’t come back!  A Black Hole is an object either big enough (has enough mass) or small enough that its escape velocity exceeds the speed of light.   Nothing, not even light, can travel fast enough to escape its gravity.


National Science Week 2005


March 14

Einstein’s Birthday

Any object (or collection of objects) can be a black hole provided its mass is large enough and/or its size small enough.  If the mass of the Sun was compressed into a 2 km ball, it would be a black hole.  It was gravity wot done it.  Gravity is action at a distance, whatever that is.

The life story of stars.  John shows  how gravity drives the stellar life-cycle from birth in nurseries like the Eagle Nebula and Pleiades, to old age like the Crab Nebula, and ‘death’ like the super-massive black hole at the centre of the Andromeda galaxy.  Powered by gravity.  Enter Einstein on his birthday.  Space-time: matter tells space how to bend; space tells matter how to move

Space-time is like a plastic sheet;  Space-time is ‘bent’ by a mass; Black holes warp space-time; Velocity close to the speed of light plays tricks. Black holes cause ‘frame dragging’ - they drag space-time around with them; Black holes evaporate via ‘Hawking Radiation’;  Black holes bend light (an effect first claimed measured by the Eddington expeditions to Brazil and west Africa for the total eclipse of 1919).  We can now examine pictures of the ‘Einstein Cross’ — gravitational lensing. 

John demonstrates all.   Nothing up my sleeve.  “Advanced technology is indistinguishable from magic” (Arthur C Clarke)