Which of the following systems is most likely to contain a black hole?

• A. A single isolated neutron star emitting radio pulses
• B. An X-ray binary system where one object is invisible and has a mass greater than $3M_{☉}$
• C. A binary system with two visible stars, each with a mass less than $1.5M_{☉}$
• D. A system containing a white dwarf and a main-sequence star

Answer: (B)

Verified step by step guidance

1. Understand the characteristics of black holes: Black holes form when massive stars collapse, and they typically have masses greater than about 3 times the mass of the Sun (\$3\,M_{\odot}$).
2. Analyze the options given: A single isolated neutron star emits radio pulses and has a mass less than the black hole threshold, so it is unlikely to be a black hole.
3. Consider the binary system with two visible stars each less than \$1.5\,M_{\odot}$: Since both stars are visible and have relatively low masses, neither is likely to be a black hole.
4. Look at the system containing a white dwarf and a main-sequence star: White dwarfs have masses below the Chandrasekhar limit (~1.4 \(M_{\odot}\)), so this system is unlikely to contain a black hole.
5. Focus on the X-ray binary system where one object is invisible and has a mass greater than \$3\,M_{\odot}\(: The invisibility suggests a compact object, and the mass exceeding \)3\,M_{\odot}$ strongly indicates it is a black hole, as neutron stars cannot be this massive.