The mass of the black hole at the center of our galaxy can be ...

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The mass of the black hole at the center of our galaxy can be estimated using the ____ of a star orbiting it.
 
  a. semi-major axis
  b. orbital period
  c. semi-major axis and orbital period
  d. neither semi-major axis nor orbital period

Question 2

The H-R diagram main-sequence of stars has a limit at the lower-mass or energy-output end because
 
  a. low-mass stars form from the interstellar medium very rarely.
  b. low-mass objects are composed primarily of solids, not gases.
  c. pressure does not depend on temperature in degenerate matter.
  d. the lower limit represents when the radius of the star would be zero.
  e. there is a minimum temperature for hydrogen nuclear fusion (the definition of a star).

[Leostella20]

Answer to Question 1

c

Answer to Question 2

e

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Excellent

[Jossy]

TYSM