A black dwarf.
When an electron returns to its ground state it emits energy in the form of light.
The Sun.
In the Bohr model of the atom, an electron emits a photon when it moves from a higher energy level to a lower energy level.
Tritium decays by beta decay (emits high energy electron converting one neutron to a proton) resulting in Helium-3.
The Sun emits significantly more energy than Jupiter. Jupiter is a gas giant planet and does not generate its own energy like the Sun does. The Sun's energy output is the result of nuclear fusion reactions occurring in its core, while Jupiter primarily radiates the energy it receives from the Sun.
A black dwarf [See related question]
There are no "cycles". A black dwarf star is the final stage of a white dwarf - a white dwarf that has cooled down so much that it no longer emits significant amounts of radiation. The Universe is currently too young to have black dwarves; white dwarves are expected to become black dwarves in the far future.
When it no longer absorbs or emits energy from the surroundings.
it emits very high energy photons
Well, if the body emits its own light then it first has to make it. So when the light is made not all of the energy put in will become light therefore the energy created will become light, heat and sound (like a light bulb) and so the amount of energy that is wasted on heat and sound will affect the amount of light produced in the long run. Hope this helps
It's kinetic
The sun emits radiant energy
Our sun, Sol, emits large amounts of electromagnetic energy.
When an electron returns to its ground state it emits energy in the form of light.
The Sun.
Gamma
This is a radioactive isotope.