No. It is the brightest star in Andromeda; a white dwarf won't even be visible with the naked eye, even if it fairly close to us, such as Sirius B.

A drying star that has collapsed to the size of the earth and is slowly cooling off; located are lower left of the H-R diagram.

A nova (as distinct from a supernova) is produced in a close binary system where one member is a white dwarf and the other a larger, less dense star. The white dwarf 'sucks' gas from the larger star which condenses into an accretion disc around the white star's equator. When this accretion disc reaches a critical mass it interacts with material on the white star and produces a huge thermonuclear explosion. This is what we see as a nova event.

Novae are variable stars.

All of them except hydrogen.

It depends on the initial mass of the star - i.e., how much actual material it contains. The more massive a star is, the shorter its 'life'. Most stars average out at roughly the mass of the Sun (certainly within a fairly narrow range either side of it at least) and the lifetime for such stars is therefore about the same as the Sun's - about 10 billion years. Really massive stars like eta Carinae will run through their nuclear reactions at a much faster rate and so will only last for a few million years. Eta Carinae could go supernova any day now!

Mass decides a stars ultimate fate.

I think that's a pulsar.

Well, it may not always be possible to do this in every case, but there are certain things to look for.

Often a supernova will leave some relic behind, such as a pulsar or black hole, so you can look and see if there is one of these phenomena present.

Also (as in the case of the Crab Nebula) we know that there was a supernova some time in the past and we can see the result with our eyes. In this case we have a pulsar at the centre as well!

After a long time, if there are any gases present from the explosion, these may dissipate owing to the object's galactic motion or gravitational effects from passing stars (really the same thing!) so the Crab Nebula may not look quite so crablike in a few million years' time.

There is no such thing as a "bunch of White dwarfs", let alone exploding white dwarfs.

The nearest explanation would be a nova. See related question.

Because they run out of the resources they use which consist of gases. It eventually 'dies' just like you would if you didnt eat food for a long period of time.

This results in the star dying/exploding causing a supernova explosion

It is estimated to take at least several hundred trillion years.

If the Sun was replaced by Orion's star Betelgeuse , its size would completely engulf the earth. Also it would extend past the orbit of Jupiter, and most of the planets would be inside the star including Jupiter. Betelgeuse would outshine the Sun like our Sun outshines the Moon. Unfortunately the Earth would have a "Front Row Seat" when the Red SuperGiant blows itself into oblivion. The explosion would be so bright that the star in Orion (constellation) which is 640 Light Years away. Days would still change from day into night, but for a few weeks or so it would appear like there are two Suns in the sky.

this is what would happen when Betelgeuse explodes :)

One of the stars in the constellation of O'Ryan

No.

It will become a white dwarf in about 7.5 billion years time.

The life of a high mass star goes like this:

A nebula gets hot and nuclear fusion binds it into a high-mass protostar

the protostar ages into high-mass, very hot star

that hot star explodes into a supergiant, which proceeds to explode into a supernova

the supernova then shrinks into a neutron star or a black hole

the life of a low- or medium-mass star goes like this:

a nebula gets hot and nuclear fusion binds it into a low-mass protostar

the protostar ages into a low- or medium- mass,cool star

the star explodes into a red giant, the red giant explodes into a planetary nebula

the nebula shrinks into a white dwarf, which then dims into a black dwarf

i hope i was able to answer your question.

Because luminosity is a measure of brightness over distance. Also white dwarfs are a hundred times smaller than the Sun.

Most white dwarfs are a long way away and thus are difficult to see.