Any difference between type 1a supernovae and a novae

[srikar97]

Both of them have the same binary system with a white dwarf and a companion star which result in the same bang so what actually is the difference between type 1a supernovae and a novae?

 

[Drakkith]

A nova is the result of a buildup of hydrogen on the surface. Once it is compressed and heated enough a fusion chain reaction occures, forming a huge explosion from the surface of the star. The star still exists afterwards, as the surface explosion does not blow it apart.

A type 1a supernova is the result of an accumulation of matter, of any type, on the surface of the star. Once this matter adds enough mass to the star the electron degeneracy pressure can no longer hold up the star against gravity and it collapses on itself to a neutron star. This collapse is the cause of the supernova, which is many many many times more energetic than a nova.

Edit: Just found this on wikipedia's article on Type 1a supernovas:

The current view among astronomers who model Type Ia supernova explosions is that this limit is never actually attained, however, so that collapse is never initiated. Instead, the increase in pressure and density due to the increasing weight raises the temperature of the core,[3] and as the white dwarf approaches to within about 1% of the limit,[11] a period of convection ensues, lasting approximately 1,000 years.[12] At some point in this simmering phase, a deflagration flame front is born, powered by carbon fusion. The details of the ignition are still unknown, including the location and number of points where the flame begins.[13] Oxygen fusion is initiated shortly thereafter, but this fuel is not consumed as completely as carbon.[14]

Once fusion has begun, the temperature of the white dwarf starts to rise. A main sequence star supported by thermal pressure would expand and cool in order to counter-balance an increase in thermal energy. However, degeneracy pressure is independent of temperature; the white dwarf is unable to regulate the burning process in the manner of normal stars, and is vulnerable to a runaway fusion reaction. The flame accelerates dramatically, in part due to the Rayleigh–Taylor instability and interactions with turbulence. It is still a matter of considerable debate whether this flame transforms into a supersonic detonation from a subsonic deflagration.[12][15]

Regardless of the exact details of nuclear burning, it is generally accepted that a substantial fraction of the carbon and oxygen in the white dwarf is burned into heavier elements within a period of only a few seconds,[14] raising the internal temperature to billions of degrees. This energy release from thermonuclear burning (1–2×10^44 J[4]) is more than enough to unbind the star; that is, the individual particles making up the white dwarf gain enough kinetic energy that they are all able to fly apart from each other. The star explodes violently and releases a shock wave in which matter is typically ejected at speeds on the order of 5000–20,000 km/s, or roughly up to 6% of the speed of light. The energy released in the explosion also causes an extreme increase in luminosity. The typical visual absolute magnitude of Type Ia supernovae is Mv = −19.3 (about 5 billion times brighter than the Sun), with little variation.[12] Whether or not the supernova remnant remains bound to its companion depends on the amount of mass ejected

 

[Chronos]

Here is the short story:
http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980202c.html
Wiki is close enough for pedagogical purposes. A type Ia supernova is fairly unique because they detonate right at the Chandrasekhar mass limit, making them ideal standard candles. It requires special circumstances for such a detonation to occur, as wiki partially explains [albeit not to my satisfaction]. There is still a lot of debate over the mechanics behind a Ia event, but, little dissent over their intrinsic luminosity.

 

[twofish-quant]

A type Ia supernova is fairly unique because they detonate right at the Chandrasekhar mass limit, making them ideal standard candles.

Maybe. We still aren't sure what causes type Ia supernova, so we still aren't sure why they make such great standard candles. The other thing is that there is an observed correlation between the light curve shape and the absolute magnitude.

There is still a lot of debate over the mechanics behind a Ia event, but, little dissent over their intrinsic luminosity.

Also the original papers are very careful about this. If it turned out that high distance supernova Ia were very different than low-distance ones then we'd have a problem, but the paper argued that the spectra were the same, and there was no correlation between things like metalicity and the absolute magnitude.

 

[phinds]

A type Ia supernova is fairly unique because they detonate right at the Chandrasekhar mass limit, making them ideal standard candles.

I've read that there have been a couple of discoveries in recent years of "super Chandrasekhar" type Ia supernovae with masses estimated from 2.0 to 2.4 solar masses.

Were those reports likely correct? Do their discovery, if valid, bring into question the standard candle?

 

[srikar97]

well..they are used as a standard candle and moreover the reports are mostly correct but what if a cosmologist gets confused whether it is a supernova or just a nova before doing his research?

 

[Drakkith]

well..they are used as a standard candle and moreover the reports are mostly correct but what if a cosmologist gets confused whether it is a supernova or just a nova before doing his research?

That is why they go to school, so that they don't get confused. When observing a new nova or supernova many measurements are taken of its brightness and spectrum. Using these they are able to determine the distance and luminosity and whether it is a nova or supernova.

 

[srikar97]

How can one classify supernovae/novae via spectrum?

 

[Drakkith]

How can one classify supernovae/novae via spectrum?

Different nova and supernova have different spectra and will shine for varying amounts of time. I don't know the details really. I'd browse around wikipedia on the supernova and nova articles and see what you can find out.