The more compact and massive an object, the stronger the gravitational influence it exerts on its direct neighbourhood – and the stronger the deviations between general relativity’s predictions and those of Newtonian gravity.
This chapter of Elementary Einstein is devoted to the most compact objects there are. First we’ll examine neutron stars, super-dense remnants of stars, and their visible avatars, pulsars. Secondly, we’ll discuss a class of compact objects whose existence was predicted using general relativity: black holes. Black holes started out as a rather exotic theoretical idea, but nowadays, they’re an important building block of astrophysical models (for stellar evolution and for the active nuclei of certain galaxies).
Stars that are between five and forty times as massive as our sun end their lives in a spectacular way – not with a whimper, but a bang! Once their nuclear fuel is exhausted, there is an gigantic explosion called a supernova, in which the outer layers of the star are ejected into space, leading […]
When even more massive stars explode in a supernova, the collapsing central region will generically have so much mass that even neutron matter cannot halt the collapse. The collapse continues, and when this happens, a black hole is born (more precisely: a stellar black hole with one to ten times the mass of our sun). […]
Soon after the beginning of radio astronomy came the discoveries of ever more variants of active galactic nuclei. An example is shown below: The image illustrates radio observations, showing a “radio galaxy” (the tiny dot in the center) which shoots beams of highly energetic particles to the left and to the right. When they collide […]
In the physics of neutron stars and black holes, we clearly see the central role of general relativity in modern astrophysics. Relativistic physics is necessary to fully understand the most energetic phenomena in the universe – from supernova explosions of stars to the driving force that makes some active galactic nuclei the brightest objects in […]