Universe: Stars And Galaxies
6th Edition
ISBN: 9781319115098
Author: Roger Freedman, Robert Geller, William J. Kaufmann
Publisher: W. H. Freeman
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Chapter 24, Problem 27Q
To determine
The mass of the central black hole using Newton’s form of Kepler’s third law.
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Observations indicate that each galaxy contains a supermassive black hole at its center. These black holes can be hundreds of
thousands to billions of times more massive than the Sun. Astronomers estimate the size of such black holes using
multiple methods.
One method, using the orbits of stars around the black hole, is an application of Kepler's third law. The mass of the black hole
can be found by using the given equation, where a is the semi-major axis in astronomical units, P is the period in years, and k is
a constant with a value of 1 Mo X year²/ AU³.
a³
M = k-
p²
What is the mass of a supermassive black hole if a star orbits it with a semimajor axis of 959 AU and a period of 13.3 years?
mass:
Another method measures the speed of gas moving past the black hole. In the given equation, v is the velocity of the gas (in
kilometers per second), r is the distance of the gas cloud from the black hole (in kilometers), and G is Newton's gravitational
constant. In this equation, G = 1.33 ×…
what is the mass of the black hole ? give your answer as a multiple of Ms where Ms is the solar mass, Ms = 2.0 * 10^(30)
express your answer as a multiple of the solar mass mass Ms.
An AGN hosts a central Black Hole of mass 2×1038×1038 kg. The AGN emits at 1/51/5 of the Eddington limit. Find the luminosity of the AGN. Give your answer in Watts to 3 significant figures.
Chapter 24 Solutions
Universe: Stars And Galaxies
Ch. 24 - Prob. 1QCh. 24 - Prob. 2QCh. 24 - Prob. 3QCh. 24 - Prob. 4QCh. 24 - Prob. 5QCh. 24 - Prob. 6QCh. 24 - Prob. 7QCh. 24 - Prob. 8QCh. 24 - Prob. 9QCh. 24 - Prob. 10Q
Ch. 24 - Prob. 11QCh. 24 - Prob. 12QCh. 24 - Prob. 13QCh. 24 - Prob. 14QCh. 24 - Prob. 15QCh. 24 - Prob. 16QCh. 24 - Prob. 17QCh. 24 - Prob. 18QCh. 24 - Prob. 19QCh. 24 - Prob. 20QCh. 24 - Prob. 21QCh. 24 - Prob. 22QCh. 24 - Prob. 23QCh. 24 - Prob. 24QCh. 24 - Prob. 25QCh. 24 - Prob. 26QCh. 24 - Prob. 27QCh. 24 - Prob. 28QCh. 24 - Prob. 29QCh. 24 - Prob. 30QCh. 24 - Prob. 31QCh. 24 - Prob. 32Q
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- The best evidence for a black hole at the center of the Galaxy also comes from the application of Kepler’s third law. Suppose a star at a distance of 20 light-hours from the center of the Galaxy has an orbital speed of 6200 km/s. How much mass must be located inside its orbit?arrow_forwardHow close, r, to the center of a neutron star would a manned satellite be orbiting if it were at the location where the gravitational force from the star equaled the gravitational force of the Earth's surface? RN = neutron star radius = 1 × 104 kmM N = neutron star mass = 3 × 1030 kgG = universal gravitational constant = 6.67 × 10-11 N m2 / kg2g⊕ = Earth gravitational acceleration = 9.807 m/s²arrow_forwardWhat is the Schwarzschild radius (in km) of a 20 solar mass black hole?arrow_forward
- The Tully-Fischer method relies on being able to relate the mass of a galaxy to its rotation velocity. Stars in the outer-most regions of the Milky Way galaxy, located at a distance of 50 kpc from the galactic centre, are observed to orbit at a speed vrot = 250 km s−1. Using Kepler’s 3rd Law, determine the mass in the Milky Way that lies interior to 50 kpc. Express your answer in units of the Solar mass.arrow_forwardFive astronauts (A - E) are watching a star collapse to form a black hole. Which of the flight plans require that the astronaut travel faster than light? A COLLAPSING STAR THAT FORMS BLACK HOLE r=0 Singularity Time Inside of Star At B D Rs Radius of a Star Earrow_forwardThe Schwarzschild radius is the distance from an object at which the escape velocity is equal to the speed of light. A black hole is an object that is smaller than its Schwarzschild radius, so not even light itself can escape a black hole. The Schwarzschild radius r depends on the mass m of the black hole according to the equation (See image.) where G = 6.673 × 10-11 (Nm2)/(kg2) is the gravitational constant and c = 2.998 × 108 m/s is the speed of light. 1. Consider a black hole with a mass of 3.70 × 107M.. Use the given equation to find the Schwarzschild radius for this black hole. Remember that 1 M = 1.989 × 1030 kg and 1 N = 1 kg * m/s2 2. What is this radius in units of the solar radius? Remember that 1 R = 6.955 × 108 m.arrow_forward
- In 1999, scientists discovered a new class of black holes with masses 100 to 10,000 times the mass of our sun that occupy less space than our moon. Suppose that one of these black holes has a mass of 1x10^3 suns and a radius equal to one-half the radius of our moon. What is the density of the black hole in g/cm^3? The radius of our sun is 7.0x10^5 km, and it has an average density of 1.4x10^3 kg/m^3. The diameter of the moon is 2.16x10^3 miles.arrow_forwardUse the Schwarzchild formulaRs =2GM / c2whereRs = Radius of the star, in meters, that would cause it to become a black holeM = Mass of the star, in kilogramsG = A constant, called the gravitational constant= 6.7 x 10-11 m3 / kg . s2c = Speed of light= 3x108 meters per secondto determine to what length the radius of the Sun must be reduced for it to become a black hole. The Sun’s mass is approximately 2 x 1030 kilograms.arrow_forwardThe orbit of the binary pulsar PSR 1936+16, studied by Taylor and Hulse, a. is so small that the orbital period is smaller than the pulsar period. b. is growing smaller, presumably by emitting gravitational waves. c. provides evidence that it is being orbited by at least 6 planets the size of Jupiter. d. shows large changes each time an X ray burst is emitted from the system. e. contains a white dwarf and a black hole.arrow_forward
- Which of the below rotation curves best represents the orbital speeds stars in the Milky Way Galaxy would have if there were no dark matter in the galaxy? A B Distance Distance C D Distance Distance А.А В. В С. С D.D Velocity Velocity Velocity Velocityarrow_forwardIf the radius of the Sun is 7 x 108 m, how does the black hole’s radius compare? (Divide the radius of the Sun by the Schwarzschild radius). Your answer should be in the form of “The Sun is _____ times smaller/bigger than the black hole.” Rsun=7x108 m Rs=29.64kmarrow_forwardA binary pulsar orbits with radial velocity 0.00004 times the speed of light. If the difference between the rest period and the minimum period over the course of the orbit is 0.001 ms, what is the rest period of the pulsar? 25 ms Trick question: this value cannot be calculated without more information 250 ms O 2.5 msarrow_forward
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