Final answer:
A compact object with a mass of about 10 solar masses in a binary system is likely to be a black hole, as it exceeds the mass limits for both white dwarfs and neutron stars.
Step-by-step explanation:
If the mass of the compact object in a binary system is about 10 solar masses, it is likely to be a black hole. White dwarfs have a mass limit of 1.4 solar masses, known as the Chandrasekhar limit, beyond which they cannot remain stable. Neutron stars, although incredibly dense, have a typical upper mass limit of around 2 to 3 solar masses before collapsing into a black hole. Any compact object exceeding these mass limits is too massive to be a white dwarf or neutron star, and therefore, the best candidate would be a black hole. Observations of systems like Cygnus X-1, where the unseen companion's mass is about 15 times that of the Sun, provide strong evidence that black holes can exist in binary systems as massive, compact object that is difficult to visually detect.