How great must the force of gravity be to bend light in space? For example, does light crossing near the centre of our galaxy get refracted? Or would it require a much stronger force?

Question

Harper Clark · Accepted Answer

Any gravity bends light.

With very sensitive instruments, we have measured the deflection of light caused by our own sun.

Although there had been earlier attempts and claims to measure the deflection of light due to our sun's gravity, the experimental error was relatively large compared to the tiny effect being measured. Reliability in this measurement was first achieved in the 1960s. The light deflection caused by white dwarf stars is visible to a somewhat greater extent. Being similar in mass to our sun, but about the diameter of Earth, a typical white dwarf has a surface gravity about #330,000# times that at the surface of the Earth (that is about #10,000# times that at the surface of our sun). White dwarf-induced microlensing in red giant-binary systems has been detected by the Kepler space telescope.

Henry Asbill · Answer

undefined Light near the center of our galaxy does experience gravitational lensing due to the combined mass, but it is less pronounced than near a massive object like a black hole. The force of gravity required to bend light is determined by mass. Strong gravitational forces, as near massive objects like black holes, can bend light significantly.

Audrey Arnold · Answer

undefined The force of gravity needed to bend light significantly is related to the mass of the object causing the gravitational field. According to Einstein's theory of general relativity, massive objects like stars, galaxies, and black holes can bend the path of light due to their gravitational pull. This phenomenon is known as gravitational lensing.

In the case of light passing near the center of our galaxy, the gravitational force exerted by the supermassive black hole at the center of the Milky Way, known as Sagittarius A*, is indeed strong enough to cause gravitational lensing. However, the degree of bending depends on the proximity of the light to the gravitational source and the mass of the object causing the gravitational field.

For light to be significantly bent, it typically requires extremely massive objects such as black holes or clusters of galaxies. These objects have gravitational fields so strong that they can bend light to a noticeable degree, creating distortions and multiple images of background objects observed from Earth.

In summary, while the force of gravity needed to bend light is substantial, objects like the supermassive black hole at the center of our galaxy can indeed cause gravitational lensing, leading to the bending of light paths in space.