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Gravity!
In black holes and
our Solar System
Dr. Abbie Stevens
Event Horizon Telescope
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Gravity
● Gravity is a pulling force between two or more things with
mass
● The more mass something has, the stronger the
gravitational field it produces
● Two famous scientists who described gravity: Newton and
Einstein
● Mass curves space; the more mass, the more space is
curved, and thus the more gravitational pull it has
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What is a black hole?
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Myth or Fact?
Credit: Peter & Trent Ninos
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Black holes have enormous mass
● Mass: 3 Suns to billions of Suns
Credit: NASA
Credit: NASA Credit: Creative Commons
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Black holes have a huge escape velocity
● Earth’s escape velocity: ~25,000 mph
● The Moon’s escape velocity: ~5,300 mph
● A black hole’s escape velocity: 670 billion mph
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What is a black hole?
● Powerful gravity
● Even light cannot escape
Credit: NASA
8,000 miles 2,160 miles
239,000 miles
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Do you really know gravity?
● Space
● Mass
● Bending
● Newton
● Einstein
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Re-visiting: Myth or Fact?
Credit: Peter & Trent Ninos
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Hunting for a black hole
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Watching a black hole eat
Credit: NASA
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What if the black hole isn’t eating?
Black hole as ☆
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Watching a black hole bend light
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Gravitational forces in the
Solar System
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Credit: caltiva
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Relative distances in our Solar System
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Mercury:
1.5 yds
Sun:
0 yds
Neptune:
120 yds
Venus:
2.9 yds
Earth:
4 yds
Mars:
6.1 yds
Jupiter:
20.8 yds
Saturn:
38.1 yds
Uranus:
76.8 yds
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● Big swirling gas cloud
flattens under its own
gravity
● Dust clumps into rocks,
which clump into
planetesimals, which
attract more dust and
rocks by their gravity, and
become planets Real picture of a protoplanetary disk
Credit: ALMA; C. Brogan; B. Saxon
Protoplanetary nebula → protoplanetary disk
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Summary
●Mass bends space to form a gravitational field
●Black holes are ‘black’ because their escape velocity is
faster than the speed of light
●Gravity was important in the formation of our Solar System
within the protoplanetary disk
Event Horizon Telescope:
first-ever picture of a
black hole!
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Fitting the Solar System in this room: distance
● Sun – Mercury: 35 million mi
● Sun – Venus: 67 million mi
● Sun – Earth: 93 million mi
● Sun – Mars: 142 million mi
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Fitting the Solar System in this room: distance
● Sun – Mercury: 35 million mi
● Sun – Venus: 67 million mi
● Sun – Earth: 93 million mi
● Sun – Mars: 142 million mi
● Sun – Jupiter: 484 million mi
● Sun – Saturn: 889 million mi
● Sun – Uranus: 1.79 billion mi
● Sun – Neptune: 2.8 billion mi ← total size of Solar System
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Fitting the Solar System in this room: size
● Sun: 864,000 mi
● Mercury: 3000 mi
● Venus: 7500 mi
● Earth: 7900 mi
● Mars: 4200 mi
● Jupiter: 89,000 mi
● Saturn: 75,000 mi
● Uranus: 32,000 mi
● Neptune: 31,000 mi
← total size for comparison
Credit: Universe Today
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More resources
https://www.nasa.gov/topics/solarsystem/index.html
https://www.universetoday.com/
https://exploratorium.edu/ronh/weight/
CrashCourse Astronomy by PBS on YouTube (10-15 min
episodes on gravity, black holes, the Solar System, etc.)