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Black Holes

Black Holes. CORE REMNANTS. Sun-like star  WHITE DWARF Huge Star NEUTRON STAR Massive Star BLACK HOLE. BLACK HOLES. 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.

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Black Holes

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  1. Black Holes

  2. CORE REMNANTS • Sun-like starWHITEDWARF • Huge StarNEUTRONSTAR • Massive StarBLACK HOLE

  3. BLACK HOLES • 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.

  4. Gravity and Black Holes • 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?

  5. Ultra-strong gravity • 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.

  6. EVENT HORIZON • 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 horizonbecause 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

  7. Schwarzchild 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.

  8. PHOTO SPHERE Photon Sphere is the radius of the orbit of light around the black hole

  9. Detecting Black Holes • 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: • X-ray radiation • Companion Mass

  10. Cygnus X-1 • 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.

  11. Other Black Hole Candidates • Several stellar mass black hole candidates have been found: • LMC X-3 in the constellation Dorado • V616 Mon in the Monocerotisconstellation • J1655-40 in Scorpius • V4641 Sgr in Sagittarius, is the closest one, is (~ 1600 light years away)

  12. Black Hole Jets • 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

  13. Chandra Image • 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.

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