3/19/20 ASTR 1040: Stars & Galaxies More Joys of Black Holes + Our Galaxy • Black holes, their general properties – and Mr. Einsteins work S.2 (special relativity), S.3 (general relativity) • Requires some careful reading • How to detect black holes (indirectly) in close binary systems (read 18.3) • Our Milky Way Galaxy in overview, aspects of any spiral galaxy M51 • Overview read Chap 19 “Our Galaxy” Whirlpool • Homework #9 due today, new HW #10 out, all Prof. Juri Toomre TAs: Daniel Sega, Max Weiner on canvas site (new labels Lecture 20 Thur 19 Mar 2020 zeus.colorado.edu/astr1040-toomre How we will be zoom-interactive REVISIT Light and • “Raise Hand” (Max monitors “Participants”) escape cones • “Send Chat” Message (Max will act) • In both cases, Juri will get to your question or comment within at most a few minutes • Or if pressing, Unmute your mike and ask cone narrows question as gravity forces get more intense • We can adjust “how to interact”, with your advice and experience REVISIT Event Black holes horizon light cones have no hair Schwarzschild Only three radius: where numbers escape velocity describe BH ! is speed of light 2 Ergosphere: Rs = 2G mass / c spinning BH most simply: drags nearby ( Rs in km, spacetime along Rs = 3 M M in Msun) 1 3/19/20 Warping of Space by Gravity 3 aspects of falling into a black hole: 1) Spaghettified • As matter approaches the singularity… – tidal forces (difference • Gravity imposes curvature on space between gravitational force at – lights path through space will be two points) are tremendous bent by gravity – Your feet would feel a much – within the event horizon, it cannot stronger pull of gravity than climb out of the hole your head • As matter approaches event horizon… – object would be – tidal forces are tremendous �spaghettified� – object would be spaghettified Three aspects of falling into a black hole: Three aspects of falling into a black hole: 2) Gravitational Redshift 3) Time Dilation From mothership's view From mothership's view – As the probe gets closer and closer to the event horizon, – As the probe gets closer and closer to the event horizon, the light becomes more and more redshifted its clock appears to slow down • Photons lose energy climbing out of the black hole gravity well – The probe (and clock) never get to the event horizon • At the EH (from our view), photons are redshifted out of existence • It moves slower and slower, eventually freezing at the EH (zero energy) From probe's view: • From probe's view: – it heads straight – Outside world gets into the black hole blueshifted • Nothing special at • Photons gain the event horizon energy falling into the black hole – Outside world gravity well clock appears to be sped up 9 10 Black Holes Don't SUCK! • Black holes have gravity, just like Questions or Comments “normal” stars, planets etc. Then we use Break-out Rooms for ~5 minutes • The only problem is that you can get SO to exchange impressions of “how are things” close to the concentrated gravity near a black hole that you can't get out again and “spring-break plans” 2 3/19/20 Survey poll Has the Pandemic affected your spring-break plans? How to A. Yes, greatly �detect� B. Yes, somewhat black hole C. No, not yet D. Trying to figure things out 13 Cygnus Loop SNR – Home of Cyg X-1 Observing a black hole: Cygnus X-1 Cygnus X-1: Blue supergiant (strong winds) pours H + He onto accretion disk of black hole Stellar-size Views of black hole �Veil Nebula� Accretion disk Such SNR may have a BH lurking! .. but not this one Blue supergiant 3 3/19/20 SS 433 top candidate SS 443 for wild object! BH + jets another stellar-size black hole Gamma-Ray Bursts HYPERNOVA ? Collapse of very massive star > BH Questions or Comments Luminosity ~ 106 to 103 times output from galaxy Visible from across the HST universe ! REVISIT Review Poll – Size of Black Hole OVERVIEW Our Milky Way Galaxy • What does the Schwarzschild radius of a black hole (BH) depend on? C. • 100-400 billion stars • A. Both mass and chemical composition • 100,000 light years of the BH in diameter, or ~ 30,000 pc = 30 kpc • B. Radius of BH, as measured by careful o observations of its size (kilo-parsecs) • C. Only the mass of BH • Sun is located about • D. Whether BH formed in massive star supernova or in some other way 8.5 kpc from center, in the `Orion Arm Artists sketch! 4 3/19/20 Our Milky Way Galaxy Stars and gas are all moving! THIS INSPIRES A SONG! Sing our way to the Milky Way THE GALAXY -- LIGHTEN UP If we might see Milky Way from outside One-pager: o Edge-on ALL about us! Sketch of Milky Way o Spiral Sb galaxy o NGC 4414 Top 5 3/19/20 Milky Way Anatomy: Spiral Galaxy The Milky Way (fuzzy ribbon of light across the sky) • Disk: includes spiral arms -- young, new star formation • Bulge & Halo: older stars, globular clusters We might prefer to look like this! Prettier? Composite of M101 – much goes on! M101 with more distinctive spiral arms Disk is very thin! (relatively speaking) REAL Artist's sketch Galaxy NGC 4565 à nearly edge-on IMAGE! 6.