Dwarfs: Where Does Their Energy Come From?

[STAii]

Greetings.
According to my Geology textbook (it is about astronomy, i wonder why we have this in the Geology textbook) :
(sorry if translation is not really good)

... and the star continues its life until the inner nuclear reactions stop for a reason or another, in this case the star will enter into one of the death shapes ...
... death shapes are Dwarfs, Neutronic Stars (?) and Black holes ...
... we can notice from the H-R diagram that Dwarfs have a high temprature and low illumination ...

The text may seem a little bit confusing, but let me give you the summary.
The book says that a star may become a dwarf when the nuclear reactions in it stops, and later the book says that dwarf have high temprature.
My question is: Where does the temprature of the Dwarf comes if the nuclear reactions are over ?

Thanks in advance.

 

[drag]

Greetings !

Once most of the hydrogen burns out in nuclear fusion
the dominant reactions become nuclear fission. This
heats up the star and makes it expand to giant(relativly )dimensions. Eventualy the core cools somewhat and collapses.
The violence of the explosion, if any, and what the star
eventually ends up as - BH, neutron star, white or red
dwarf depends on its enitial mass.

Live long and prosper.

 

[drag]

Oh sorry... anout the dwarfs, well, nothing really
powers them - just some little random remaining nuclear
reactions and its enitial temprature as it cools.
It can not collapse into denser objects because
it's not sufficiently massive.

 

[LURCH]

AIUI, the energy in a dwarf star is from the collapse itself, plus left-over energy from previous fussion. Though fussion is no longer taking place in the core, the dwarf is a star that used to be a giant, and has fallen in on itself. The particles of heated gasses falling in toward a central point collide with one another, and this collision generates heat. This heat is trapped by the great density of the dwarf star, and takes a very long time (even in cosmological terms) to radiate away.

 

[Nereid]

Just to add to what LURCH said.

The dwarf, once the collapse has settled down, slowly cools by radiation. This takes a long time because the dwarf is so small.

If the dwarf has a close binary companion, or close planets, it may experience some heating at a future time, as material from its companion falls onto its surface or a planet is gobbled up.

Also, through orbital interactions or magnetic braking, some of the dwarf's rotational or magnetic energy may be converted into heat.