Part IV: Astrophysics & Observations
Black holes are not just theoretical constructs—they're real astrophysical objects. From stellar-mass black holes in X-ray binaries to supermassive black holes powering quasars, observational evidence for black holes is now overwhelming.
Part Overview
Black holes form from stellar collapse and grow via accretion and mergers. Stellar-mass black holes (3-100 M☉) form when massive stars exhaust their fuel. Supermassive black holes (10⁶-10¹⁰ M☉) reside at galactic centers. Accreting matter forms luminous accretion disks emitting X-rays. The Event Horizon Telescope imaged M87*'s shadow in 2019. LIGO detected gravitational waves from merging black holes starting in 2015, opening a new observational window.
Key Topics
- • Stellar black hole formation via core collapse supernovae
- • Supermassive black holes and galaxy evolution
- • Accretion disks: Shakura-Sunyaev model, Eddington limit
- • X-ray binaries: Cygnus X-1 and the first black hole candidates
- • Event Horizon Telescope: imaging M87* and Sgr A*
- • LIGO/Virgo detections: gravitational waves from BH mergers
6 chapters | Real black holes | From formation to observation
Chapters
Chapter 1: Stellar Black Hole Formation
Stars with initial mass can form black holes. Nuclear fusion halts, core collapses, supernova explosion (Type II). If remnant mass (Tolman-Oppenheimer-Volkoff limit), neutron degeneracy pressure fails, collapse to a black hole. Observed stellar BH masses: 3-100 M☉. Pair-instability supernovae may leave no remnant for .
Chapter 2: Supermassive Black Holes
Nearly every galaxy hosts a supermassive black hole at its center. Masses: 10⁶-10¹⁰ M☉. Sgr A* at the Milky Way center: . M87*: . Formation mechanisms: direct collapse, runaway mergers, primordial black holes. M-sigma relation: ties BH mass to galaxy velocity dispersion. Co-evolution of galaxies and black holes. AGN feedback.
Chapter 3: Accretion Disks and Jets
Matter falling toward a black hole forms an accretion disk due to angular momentum conservation. Viscosity transports angular momentum outward, allowing matter to spiral inward. Shakura-Sunyaev α-disk model. Temperatures: K, emitting X-rays. Eddington luminosity: maximum luminosity from spherical accretion. Relativistic jets: launched perpendicular to disk, powered by Blandford-Znajek mechanism extracting BH rotation energy.
Chapter 4: X-Ray Binaries
A black hole in a binary system accretes from its companion star, emitting X-rays. Cygnus X-1 (1964): first BH candidate, confirmed via dynamical mass measurement . High-mass X-ray binaries (HMXB): massive companion. Low-mass X-ray binaries (LMXB): low-mass companion. Quasi-periodic oscillations (QPOs) probe spacetime near ISCO. Spectral states: thermal, hard, steep power-law.
Chapter 5: Event Horizon Telescope
Earth-sized radio interferometer array imaging black hole shadows. 2019: first image of M87* shadow—a dark region surrounded by a bright photon ring from the accretion disk. Diameter ~40 μas, consistent with GR predictions. 2022: image of Sgr A* (our galactic center BH). Direct visual evidence for event horizons. Testing strong-field GR. Measuring BH mass and spin from shadow size and shape.
Chapter 6: Gravitational Waves from BH Mergers
LIGO's first detection (GW150914, 2015): two black holes () merged, emitting gravitational waves. Over 90 BH merger detections to date. Inspiral-merger-ringdown waveforms. Testing GR in strong-field regime. Measuring BH masses and spins. Population studies reveal BH mass distribution. GW190521: intermediate-mass BH. Future: LISA space-based detector for SMBH mergers. Multi-messenger astronomy era.
Course Navigation
Prerequisites:
- • Part I: Black Hole Basics
- • Part II: Rotating & Charged BHs
- • Basic astrophysics and stellar evolution