A neutron star contains about the same mass as the Sun squeezed into a sphere about 10 miles in diameter. Such a dense object exerts a tremendous gravitational force that, when part of a binary star system, is capable of pulling in gas from the neighboring star. This gas spirals onto the neutron star via an orbiting swirl called an accretion disk, which is visible in many wavelengths, particularly in X rays. Previous measurements have been made only where gravitational fields are weak, such as in our solar system. The Rossi Explorer is the first instrument that has allowed us to actually see how matter moves in the strong gravitational field near a neutron star.
X rays carry that message.
The newly discovered signals may be the key that unlocks the door, so we can see what the right explanation is. This refers to the dragging of inertial frames, a qualitatively new prediction of Einstein's theory of gravity. Lamb compares orbiting gas and the dragging of inertial frames around a neutron star to a marble rolling down a large funnel covered with fabric. As the object turns, it will twist the fabric, stretching it. The marble will start to roll toward the center of the funnel, but it soon deviates to the side because the fabric is moving and carries the marble with it.