abstract:The concept of mass in general relativity (GR) is more complex than the concept of mass in special relativity. In fact, general relativity does not offer a single definition for the term mass, but offers several different definitions which are applicable under different circumstances.
General relativitypredicts that the wavelengthofthislightwill beshifted by a small amountdue to thegalaxies'mass, in an effectcalledgravitationalredshift.