 Sun-like star  WHITE DWARF  Huge Star  NEUTRON STAR  Massive Star  BLACK HOLE

 If the core remnant has a mass greater than 3 solar masses, then not even the super- compressed degenerate neutrons can hold the core up against its own gravity.  Gravity finally wins and compresses everything to a mathematical point at the center. The point mass is a black hole.  Only the most massive, very rare stars will form a black hole when they die.  As the core implodes it briefly makes a neutron star for just long enough to produce the supernova explosion.

 Escape velocity –velocity necessary to escape gravitation pull of an object  Earth –11 km/s  Anything moving at less than escape velocity will eventually be pulled back to object  What happens when escape velocity is greater than the speed of light?

 The gravity of the point mass is strong enough close to the center that nothing can escape, not even light!  Within a certain distance of the point mass, the escape velocity is greater than the speed of light.

 Astronomers use the distance at which the escape velocity equals the speed of light for the size of the black hole.  This distance is called the event horizon because no messages of events happening within that distance of the point mass make it to the outside.  If you use the speed of light (c) for the escape velocity you find the event horizon is at a distance of  This radius is also called the Schwartzchild radius

 Any mass can become a black hole if it collapses down to the Schwarzschild radius –  If a mass is over 3 solar masses and has no fusion process to keep it from collapsing, then gravitational forces alone make the collapse to a black hole inevitable.  Down past electron degeneracy, on past neutron degeneracy and then on past the Schwarzchild radius to collapse toward zero spatial extent - the singularity.  The Schwarzschild radius (event horizon) just marks the radius of a sphere past which we can get no particles, no light, no information.

 Photon Sphere is the radius of the orbit of light around the black hole

 You cannot see a black hole directly, instead, you detect their effect on surrounding material and stars.  If the black hole is in a binary system and its visible companion is close enough to the black hole, then the effects will be noticeable.  There are two signatures of a black hole in a binary system: 1. X-ray radiation 2. Companion Mass

 Doppler studies of this blue supergiant in Cygnus indicate a period of 5.6 days in orbit around an unseen companion.  The B-type blue supergiant (HDE226868) is projected to have a mass of about 25 solar masses.  The mass of the companion is calculated to be 8-10 solar masses, much too large to be a neutron star.

 Several stellar mass black hole candidates have been found:  LMC X-3 in the constellation Dorado  V616 Mon in the Monocerotis constellation  J in Scorpius  V4641 Sgr in Sagittarius, is the closest one, is (~ 1600 light years away)

 Black hole jets are one of the great paradoxes in astronomy  How is it that black holes, so efficient at pulling matter in, can also accelerate matter away at near light speed?  Scientists still don't know how these jets form, but now have a solid idea about what they're made of  Scientists generally agree that the jets must be made either of electrons and their antimatter partners, called positrons, or an even mix of electrons and protons

 January 10, 2008—A new ultradeep image of the nearby galaxy Centaurus A offers the best view yet of the effects of an active supermassive black hole.  The image, taken by the space-based Chandra X-Ray Observatory, reveals a powerful jet of high-energy particles that extends for 13,000 light-years. A weaker counterjet points in the opposite direction.  Astronomers think the jet is created by energy escaping as matter falls into a supermassive black hole at the center of the galaxy, a system known as an active galactic nucleus.  Such jets likely deliver energy to the rest of the galaxy, fueling star formation.