Gravity overwhelms all other forces, and all matter falls deep into the star. The star becomes smaller and smaller, denser and denser. As it collapse, the escape velocity increases until it is equal to or grater then the escape velocity of light. Not even light is fast enough to escape from the pull of gravity. We cannot see black holes, because they emit no light energy.
Black holes have tremendous gravitational forces.
Also a black hole will sucks up any material near it. This companion is pulling gas and dust away from the giant star. The Universe for the Beginner, by Patrick Moore, p. 22 4. The density of the singular state is 10 to the 94 grams per cubic centimeter, or 10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 times the density of water. The science of the Universe by Edward R. Harrison, p. 186 5.