6 Chapter 6 – What’s a black hole?
OpenStax Astronomy Chapter 24: Black Holes and Curved Spacetime
Stellar Mass Black Holes
I. Black Holes
A. If the of a star exceeds Msun, it will to a
B. Can two ways:
1. : if star was enough, will keep down into a black hole
2. : neutron star in a system exceeds mass limit
C. Black Hole: very (no size) and very
1. Not even travels fast enough to its
Black holes are formed by…
A. A lack of light in a region of space
B. Supernovae from the most massive stars
C. Supernovae from binary stars
D. Collapsed dark nebulae
Understanding Black Holes – Special Relativity
II.
A. theory published in 1905
B. and are the thing:
C. can travel than the , it is the Universe’s ultimate speed
D. : -dimensions, both space and time on our
III. and Reference frames
A. Usually, depend on the between objects, or (where are from)
1. Example: Throw ball out window of car going 50 mph in same direction car is moving. of ball looks from in car (25 mph), side of road (75 mph), or in car going other way (125 mph)
B. , will see that moves at the (c) regardless of their or reference frame
1. Example: Spaceship going by the Earth at half the speed of light (0.5c) and emits light, we’ll still see the light pass by the Earth at speed of , not c + 0.5c
C. passes more in a reference frame
1. : Moving clock runs
2. : twin on fast moving spaceship ages than twin on Earth
D. An object is in than it is at rest
1. Length : shorter in of motion
2. Example: Meter stick moving at 90% of speed of light is only m long
General Relativity
Sec 24.1, Sec 24.2, Sec 24.4, Sec 24.7
IV.
A. Einstein’s theory of (1915), predicts black holes
B. the geometry of
C. results from the of objects move through
D. of depends on shape of spacetime, can be by gravity
1. Gravitational : Light travels on the of spacetime, so can the path of
E. Gravity
1. Gravitational : Because appears to down, light appears to have frequency, meaning longer , meaning
2. Example: satellites must account for this
F. Gravity causes in spacetime
1. Gravitational waves: in the fabric of that move at the speed of
2. Detected with (Laser Interferometer Gravitational Wave Observatory) in Livingston, LA and Washington state in 2015
Photons have no mass, and Einstein’s theory of general relativity says:
A. Their paths through spacetime are curved in the presence of a massive body
B. Their apparent speeds depend on the observer’s frame of reference
C. They should not be attracted to a massive object
D. Their wavelengths must remain the same as they travel through spacetime
Black Holes with Relativity
V. in spacetime
A. : extreme or small and deep in spacetime
1. No size or
2. Can’t explain the there
B. : of black hole, Schwarzschild radius
1. Where from inside because the from the black hole’s gravity is the , nothing can go fast enough to escape
2. Time here, time dilation at most extreme
3. Very : Event horizon of 1 Msun black hole about miles across
4. forces and gravitational
a. Example: Force between your head and foot about a times more than Earth’s gravity
Finding Black Holes
VI. Black Holes
A. Can be found by of their on
B. See from systems that include a
C. See Gravitational from binary or black holes
Black holes that are stellar remnants can be found by searching for:
A. dark regions at the centers of galaxies
B. extremely luminous infrared object
C. variable X-ray sources
D. objects that emit very faint radio emission
Tutorial Activity – Black Holes
“Elementary Astronomy Worksheet Handout 20: Stellar Remnants” (modified by Kaisa E. Young) by Catherine Whiting via OER Commons, licensed under CC BY 4.0, https://oercommons.org/courses/elementary-astronomy-worksheets
1. What is a black hole?
2. How do stellar-mass black holes form?
3. What would happen to the orbit of the Earth if the Sun were to suddenly become a black hole?
4. Partner A will take a journey into a black hole. Partner B will stay safely away from the black hole and watch. Partner A will carry a clock and emit a blue light signal towards Partner B. Describe what Partner B will observe as Partner A falls in:
(a) How will the time on Partner A’s clock compare with the time on Partner B’s clock?
(b) How will the blue light look to Partner B?
(c) What else might Partner B observe as Partner A gets near and crosses the Event Horizon?
