Concept explainers
Surviving the Plunge. The tidal forces near a black hole with a mass similar to that of a star would tear a person apart before that person could fall through the event horizon. Black hole researchers have pointed out that a fanciful “black hole life preserver” could help counteract those tidal forces. The life preserver would need to have a mass similar to that of an asteroid and would need to be shaped like a flattened hoop placed around the person’s waist. In what direction would the gravitational force from the hoop pull on the person’s head? In what direction would it pull on the person’s feet? Based on your answers, explain in general terms how the gravitational forces from the “life preserver” would help to counteract the black hole’s tidal forces.
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The Cosmic Perspective (9th Edition)
- A stellar black hole may form when a massive star dies. The mass of the star collapses down to a single point. Imagine an astronaut orbiting a black hole having eight times the mass of the Sun. Assume the orbit is circular. a. Find the speed of the astronaut if his orbital radius is r = 1 AU. b. Find his speed if his orbital radius is r = 11.8 km. c. CHECK and THINK: Compare your answers to the speed of light in a vacuum. What would the astronauts orbital speed be if his orbital radius were smaller than 11.8 km?arrow_forwardA black hole is an object with mass, but no spatial extent. It truly is a particle. A black hole may form from a dead star. Such a black hole has a mass several times the mass of the Sun. Imagine a black hole whose mass is ten times the mass of the Sun. a. Would you expect the period of an object orbiting the black hole with a semimajor axis of 1 AU to have a period greater than, less than, or equal to 1 yr? Explain your reasoning. b. Use Equation 7.6 to calculate this period.arrow_forwardThe next step in deciding whether the object in Exercise 25.25 is a black hole is to estimate the density of this mass. Assume that all of the mass is spread uniformly throughout a sphere with a radius of 20 lighthours. What is the density in kg/km3? (Remember that the volume of a sphere is given by V=43R3 .) Explain why the density might be even higher than the value you have calculated. How does this density compare with that of the Sun or other objects we have talked about in this book?arrow_forward
- Since the force of gravity a significant distance away from the event horizon of a black hole is the same as that of an ordinary object of the same mass, Kepler’s third law is valid. Suppose that Earth collapsed to the size of a golf ball. What would be the period of revolution of the Moon, orbiting at its current distance of 400,000 km? Use Kepler’s third law to calculate the period of revolution of a spacecraft orbiting at a distance of 6000 km.arrow_forwardUse the result from Exercise 24.21 to calculate the radius of a black hole with a mass equal to: the Earth, a B0-type main-sequence star, a globular cluster, and the Milky Way Galaxy. Look elsewhere in this text and the appendixes for tables that provide data on the mass of these four objects.arrow_forwardIn 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_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 1×1021×102 suns and a radius equal to one-half the radius of our moon. A)What is the density of the black hole in g/cm3g/cm3? The radius of our sun is 7.0×105km7.0×105km, and it has an average density of 1.4×103kg/m31.4×103kg/m3. The diameter of the moon is 2.16×1032.16×103 miles. 1km=0.6214mile1km=0.6214mile.?arrow_forwardYou discover by dropping particles into it that the Event Horizon (Schwartzschild Radius) of a black hole is 171 km. How massive is it? (enter just the number in solar masses)arrow_forward1. Let’s say we have a black hole with a mass 10 times that of the Sun (the Sun’s mass is 2 x 1030kg so the mass of the black hole is then 2 x1031 kg) Using the definitions for G and c what Schwarzschild radius of this black hole be? g=6.67 x 10-11 m3 kg-1 s-2 c=3 x 108 m s-1arrow_forward
- Nothing can escape the event horizon of a black hole, not even light. You can think of the event horizon as being the distance from a black hole at which the escape speed is the speed of light, 3.00 × 108^8 m/sm/s, making all escape impossible. What is the radius of the event horizon for a black hole with a mass 7.5 times the mass of the sun? This distance is called the Schwarzschild radius.arrow_forwardIn 1999 scientists discovered a new class of black holes with masses 100 to 10,000 times the mass of our sun but occupying less space than our moon. Suppose that of these black holes has a mass of 1x10^3 sun's and radius equal to one-half the radius of our moon. What is the density in grams per cubic centimeter? The mass of the sun is 2.0x10^30 kg and the radius of the moon is 2.16x10^3 mi.arrow_forwardWhat is the Schwarzschild radius (in km) of a 20 solar mass black hole?arrow_forward
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