Class notes
ASTRO 101: Black Holes Module 9
- Course
- ASTRO 101
- Institution
- University Of Alberta (UofA)
Notes for ASTRO 101 based on the official Coursera videos for the class. Covers Module 9.
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Module 9Black Hole Observations
● History & Motivation:
○ Astronomers have studied black holes since 1963.
○ Despite decades of research, many mysteries remain unsolved.
○ Continued funding for advanced telescopes is needed to probe deeper into
black hole physics.
● Unanswered Questions:
○ What more can be learned about black holes?
○ Why haven't astronomers fully understood black holes after 50+ years?
● Black Hole Binaries:
○ Key systems for research: black holes paired with companion stars.
○ Companion stars send mass toward the black hole.
■ Mass travels through a disk and corona or is ejected via jets.
● Observation Techniques:
○ Visible light alone is insufficient for detailed study.
○ Multi-wavelength observations (radio, infrared, ultraviolet, X-ray) provide a
fuller picture.
○ Different wavelengths reveal the physics of binary components.
● Changing Properties of Black Holes:
○ Black hole properties evolve over time.
○ Brightness depends on feeding activity ("eating").
■ Feeding rates vary: slow (like tea) vs. rapid (like a pie-eating contest).
○ These feeding dynamics influence observations across wavelengths.
Black Hole Feeding and Observation
● Feeding Behavior:
○ Black holes alternate between feeding (active) and resting (inactive).
○ Brightness and emission wavelengths depend on feeding activity.
● How Black Holes Feed:
○ Material (e.g., stars, gas clouds, dust, even astronauts) drawn too close is
pulled into the accretion disk.
○ Feeding generates emissions across the electromagnetic spectrum (radio to
gamma rays).
, ● Scientific Insights from Feeding Black Holes:
○ Actively accreting black holes allow astronomers to study:
■ The type of material being consumed.
■ Physics of feeding processes and tests of general relativity in
extreme gravity.
○ Doppler shift from the rotating accretion disk provides information:
■ Blueshifted light (disk side moving toward us).
■ Redshifted light (disk side moving away).
● Models Explaining Black Hole Behavior:
○ Corona models:
■ "Lamp Post Model" vs. "Sandwich Model."
○ Jets have two types (flavors) that require further observation to understand.
● Challenges of Non-Feeding Black Holes:
○ Hungry black holes drifting through space are nearly invisible due to the
lack of emitted light.
○ Isolated black holes are detected via gravitational lensing:
■ Their strong gravitational field curves spacetime, warping light from
distant stars or galaxies.
● Wide vs. Close Binary Systems:
○ Wide Binary Systems:
■ Easier to study; black hole's mass and size can be determined from
the distinct light of the companion star and accretion disk.
○ Close Binary Systems:
■ Material from the companion gets so bright that it outshines the
star, making it harder to distinguish light sources.
■ Analogy: Like spotting a firefly above a campfire across a dark field.
Stellar-Mass Black Holes and X-Ray Binaries
Stellar-Mass Black Hole Identification
● Companion Stars:
○ Black holes are easier to locate when they have companion stars due to
gravitational effects.
○ X-ray binaries (low mass and high mass) are key systems for identifying
black holes.
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