A disk of gas surrounding a star . The star may be a white dwarf , a neutron star , or a stellar black hole in a close stellar binary system. In these cases, the material of the accretion disk comes from the nearby companion star of the binary system. Accretion disks may also surround newborn stars or the massive black holes found in the centers of many galaxies. The smallest part of a chemical element, such as hydrogen, helium, or carbon.
Atoms possess a compact nucleus surrounded by one or more electrons .
To escape would require a speed greater than that of light , which is not allowed. Chemical burning A chemical reaction among atoms or molecules that releases energy, such as heat or light. There are also chemical reactions that require the input of energy. An example is photosynthesis, in which carbon dioxide and water are combined to form plant material and molecules of oxygen. The energy for this chemical reaction is provided by sunlight.