Exam 13: Bizarre Stellar Graveyard

When we see X-rays from an accretion disk in a binary system, we can't immediately tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following phenomena in this system. Which one would rule out the possibility of a black hole?

All massive-star supernovae leave behind black holes as remnants.

Consider again the civilization described in the previous question. (They live on a planet orbiting 10 AU from a close binary star system that consists of a 15 MSᵤn red giant star and a 10 MSᵤn black hole surrounded by an accretion disk.) Through a bizarre (and scientifically unexplainable) fluctuation in the space-time continuum, a copy of a book from that civilization arrives on your desk; it is entitled Iguoonos: How We Evolved. In the first chapter, you learn that these beings evolved from organisms that lived 5 billion years ago. Which of the following statements should you expect to find as you continue to read this book?

The surface of the neutron star RXJ2015 has a temperature of 10 million K. This neutron star glows most strongly in

Brown dwarfs, white dwarfs, and neutrons stars are all kept from collapsing by degeneracy pressure.

Which of statement below about black holes is not true?

If you had something the size of a sugar cube that was made of white dwarf matter, it would weigh ________.

Imagine an advanced civilization living on a planet orbiting at a distance of 10 AU (1.5 billion kilometers) from a close binary star system that consists of a 15 MSᵤn red giant star and a 10 MSᵤn black hole. The black hole is surrounded by an accretion disk. Sometime within the next million years or so, the civilization's planet is likely to be doomed because ________.

The maximum mass of a white dwarf is ________.

Degeneracy pressure stops the crush of gravity in all the following except:

Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass limit?

The more massive a white dwarf, the ________.

The Crab Pulsar is pulsing in visible light 30 times per second. Why?

What is the upper limit to the mass of a white dwarf?

According to our modern understanding, what is a nova?

How is an X-ray burst (in an X-ray binary system) similar to a nova?

Which of the following is closest in mass to a white dwarf?

Which of the following statements about degeneracy pressure is not true?

What is the ultimate fate of an isolated white dwarf?

"Negatively Defined" Objects: Summarize the best observational evidence that astronomers have for the existence of stellar mass black holes. Contrast this with the observational evidence that pulsars exist. Do you agree or disagree with the statement that the best evidence we have for stellar mass black holes is that we have detected objects for which an alternate explanation is lacking? How does your answer influence your confidence in the existence of black holes? Does the strong observational confirmation of Einstein's general theory of relativity (see Special Topic General Relativity and Spacetime in Section 13.3) increase your confidence in the existence of black holes? Should it?