Black Holes Have students take notes during the presentation.

What do you think of when you hear the term “black hole?” Actually an infinitesimally tiny spot, the remains of the supernova of a high mass star. So much gravity that even light can’t escape Show rolling can trick: line up seam so will roll down hill, then up hill the next time. Show inside of can – centre of gravity is changed by row of rocks. Gravity is still a mystery to us too. Hopefully this presentation you’ll have a better understanding of black holes and their huge gravitational forces.

Galactic Centre in Infrared Wavelengths DO STRETCHY FABRIC BLACK HOLE with this slide up: “Demo” (with a couple students to help you) a ping pong ball rolling around a heavy mass (rock). Rock is object in space that warps the fabric of space time (black fabric). Ping pong ball is an object in orbit. Video clip is evidence for the supermassive black hole at the centre of the milky way goes from 1992 to 2006. The central region of our Milky Way is an extremely interesting and fascinating field of research. Within few light years we find here ten thousands of stars forming a dense cluster, and the geometric centre of our Galaxy harbours a supermassive black hole with around 3.6 million solar masses. Due to its relative proximity of around 8 kiloparsecs (26,000 ly), the Galactic Centre is a perfect laboratory to examine the physical processes in a galactic nucleus. Stars moving at about 3 million miles per hour (10 times as fast as a normal star) because pulled by the powerful gravity of the bh. Data from IR telescope at Keck in Hawaii www.mpe.mpg.de/ir/GC/

How do Black Holes form? Stellar Mass Black Holes Probably in a supernova, an exploding star (the star is likely 25 times the mass of our sun) Or possibly when two neutron stars collide

How do Black Holes form? Supermassive Black Holes Found at the centre of most (all?) galaxies, millions to billions the mass of our sun Maybe formed by a stellar black hole accumulating material over time? Or black holes colliding?

What if the Sun became a black hole? It couldn’t but if it did, we’d feel exactly the same amount of gravity as we do now. We’d continue to orbit as per usual. Stellar mass black holes aren’t a problem unless you are within a few km of it. Supermassive black holes do gobble up stars though. But they are at the centre of galaxies only, far from us!

What if you fall into a black hole? You are doomed Gravity 1000 times stronger on feet than head “Spaghettification” Dead in a few milliseconds Inside event horizon, can’t ever escape (escape velocity = c) Matter collapses down to a point, a singularity C = speed of light 300,000km/s

Schwarzschild Radius Escape velocity is the speed needed to escape the gravity of an object. vesc = (2GM/R)1/2 where G=6.67x10-11m3/kgs2 The Schwarzschild Radius is where the escape velocity = the speed of light. So the radius can be calculated: R = 2GM/c2 where c=3x108m/s or 300,000km/s G is the universal gravitational constant M is the mass of the object R is the radius from the centre of the object C is the speed of light We will NOT be doing these calculations. Students don’t really need to copy these out.

Inevitaable Mathematics Scientists believe that if an object reaches the Schwarzschild radius, the object will inevitably be pulled into the black hole. Some mathematical expressions and operations result in a numerical black hole no matter where you start…

Inevitable Mathematics Start with a Number (positive integer) 5 7 Multiply it by 6 Add 12 to the result Divide by 3 Subtract twice the original number For 5: x6=30, +12=42, /3=14, -2(5)=4 For 7: x6=42, +12=54, /3=18, -2(7)=4

Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) GLAST Burst Monitor (GBM) An example of a multiwavelength mission to be launched next year… “GLAST will consist of 2 instruments…” LAT – Has a wide field of view. 20MeV to 300 GeV detection range by “pair production” (gamma-ray interacts with layer of tungsten producing electron positron pair which are tracked to determine gamma-ray originating position and energy) GBM – observes bursts down to 10 keV, will trigger telescope to re-point toward the burst (which are the most energetic objects in the universe, next to the big bang, but only last a minute or less then are gone forever) Launch was June 11, 2008 – Click here to view launch

For More Information: GLAST http://www-glast.sonoma.edu Black Holes http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html