Black hole | ||||
What is a star? | Automatic translation | Updated June 01, 2013 | ||
A star is a aster like the sun shining through nuclear reactions that occur in the middle. | The number of stars in the universe is estimated between 1022 and 1023. Apart from the Sun, the stars are too faint to be observed in daylight. Image: Birth of a star: image made from data of X-ray telescope Chandra (blue) and data from the Spitzer Infrared Telescope (red and orange). NB: The astronomers classify stars in dwarf or giant. | |||
What is a black hole? | ||||
Black holes are massive objects whose gravitational field is so intense that it prevents any form of matter or radiation to escape. Black holes are described by the theory of general relativity. When the heart of the dead star is too massive to become a neutron star, it shrinks inexorably to form the astronomical object that is the black hole. The stellar black holes have a mass of few solar masses. They arise as a result of the gravitational collapse of massive stars of the residue (about ten solar masses or more). | The light can not overcome the gravitational force and surface remains trapped. Image: V. Beckmann (NASA's GSFC) et al., ESA |