There is another way light can be redshifted besides the doppler effect – gravitational redshifting.
In physics and general relativity, gravitational redshift (known as Einstein shift in older literature) is the phenomenon that electromagnetic waves or photons travelling out of a gravitational well (seem to) lose energy. This loss of energy corresponds to a decrease in the wave frequency and increase in the wavelength, known more generally as a redshift.
The second cause of redshift is gravity – and this gravitational redshift is the effect detected in the latest results from the international team led by Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics in Germany.
Due to gravitational redshift, its image reddens over time as the object moves away from the observer.
Equally common is the idea that matter can be observed falling into a black hole. This is not possible. Astronomers can detect only accretion disks around black holes, where material moves with such speed that friction creates high-energy radiation that can be detected (similarly, some matter from these accretion disks is forced out along the axis of spin of the black hole, creating visible jets when these streams interact with matter such as interstellar gas or when they happen to be aimed directly at Earth). Furthermore, a distant observer will never actually see something reach the horizon. Instead, while approaching the hole, the object will seem to go ever more slowly, while any light it emits will be further and further redshifted.
The amount of gravitational redshift depends on the density of the object. So the compact objects such as white dwarfs and neutron stars show more gravitational redshift than normal stars such as the Sun. Black holes have infinite gravitational redshift.
Gravitational redshift, an effect predicted by Albert Einstein that is crucial for maintaining the Global Positioning System (GPS) on Earth, has been observed in a star system in our galaxy.
Within Einstein’s general theory of relativity there is an effect known as “gravitational redshift,” in which light becomes redder because of the influence of gravity; the wavelength of a photon, or light particle, gets longer and appears redder as the wavelength climbs farther away from a gravitational well.