The T. Coronae Borealis is a binary system. It is actually two stars, ... pushed into outer space. What's left behind is a leftover core of the star - that's called a white dwarf.
The nuclear fusion reaction no longer takes place, which makes white dwarfs very dim. They are still pretty hot, though, and they're super dense, with a mass comparable to our Sun squeezed into a volume resembling the Earth.
Its companion star is in the red giant phase, where it is puffed up. Its outer parts are getting sloughed off and pushed into space. The material that is coming off the red giant is now falling onto the white dwarf.
[
add
]
[
|
|
...
]