How might scientists detect
and locate black holes?

Astronomers can detect them by watching for their effects on nearby stars and gas. ... The star clusters then sink to the center of the galaxy, where the intermediate-mass black holes merge to form a supermassive black hole.

the body's situation won't change the forces are equal opposit and on the same body

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.