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lensman57

A Question about the SN in M82

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Hi,

I don't know if this is the right forum for posting this question so please bear with me. Does anyone know if a super nova is almost instantaneous or the build up and release of the energy and light takes place over a short period, by which I mean days or weeks?

Many thanks for your help.

Regards,

A.G

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Hi AG. The SN in M82 is a type Ia supernova. I think the typical light curve on these is an increase over 1-2 weeks from discovery to max brightness and then a gradual decline over several more weeks / months. 

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In a way both.

Betelgeuese will go supernova we know (hopefully) that from the mass of it.

If you count it going to a red giant first then eventually the fuel being used then the process takes a few million years.

When all the fuel is used up and the core collapses then explodes this bit is fast, very fast.

Take your pick.

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Thank you both for your informative replies. If this SN follows a specific light curve then will it be possible to work it backwards to determine when it actually went super nova or do we generally accept the time of the discovery as the reference point in another word could it have gone super nova long before it was discovered?

Regards,

A.G

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 If this SN follows a specific light curve then will it be possible to work it backwards to determine when it actually went super nova ...?

Regards,

A.G

Yes. It would be possible to compare SN2014J's partial light curve with historical SN light curve data to enable any gaps to be filled in.

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I think what the OP was asking was how long does it take for an object to go from a star to a supernova and the answer is... only 100 seconds :shocked::eek:

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Supernova's happen very quickly, in the order of seconds. However the light curve takes a while to build up to full intensity. This is from various factors, from things like newly formed elements being radioactive and decaying, to secondary effects hitting the shell of expanding material and making it brighter. So it goes bang very quickly, but brightens as the shell expand, and getting reheated by various processes. Eventually these decay, leading to the drop in light levels.

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One of the nicest things about supernova light curves is that they vary with distance in good agreement with Relativity. They are bright enough to be seen at huge distances, therefore at huge recession velocities, and their clocks (what's left of them  :grin: ) tick at a different rate to ours.

This is a splendid read; http://www.amazon.com/The-Supernova-Story-Laurence-Marschall/dp/0691036330

Olly

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Worth adding that most of the light we see from a supernova isn't from the 'explosion' itself, but rather from the radioactive decay of unstable elements created during the initial event - so the 'supernova' we see is already the aftermath of what's gone before. 

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Agreeing with the details above:

SN 2014J in M82 was a Type 1a SN, characterized by the distinctive light curve that it has (and still is) produced.

The great thing about Type 1a SN is that they are all Identical. They occur within binary star systems where a white dwarf is accreting mass from another star (can range from a supergiant to another white dwarf), when the mass of the accreting white dwarf reaches 1.44 solar masses (Chandrasekhar Limit) they stat is no longer able to prevent a catastrophic collapse causing the SN to occur. As a result of all Type 1a's being produced by the same process they all produce a same maximum absolute magnitude of -19.3 and are ideal for use as a standard candle when calculating distances.

Type 1a's usually brighten over a couple of weeks but then the brightness fades gradually of the coming months. SN 2014J is slightly strange though because its brightness increased more rapidly than normal, this has thrown up questions as to what is a typical Type 1a SN?, research is still on going.

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Agreeing with the details above:

SN 2014J in M82 was a Type 1a SN, characterized by the distinctive light curve that it has (and still is) produced.

The great thing about Type 1a SN is that they are all Identical. They occur within binary star systems where a white dwarf is accreting mass from another star (can range from a supergiant to another white dwarf), when the mass of the accreting white dwarf reaches 1.44 solar masses (Chandrasekhar Limit) they stat is no longer able to prevent a catastrophic collapse causing the SN to occur. As a result of all Type 1a's being produced by the same process they all produce a same maximum absolute magnitude of -19.3 and are ideal for use as a standard candle when calculating distances.

Agreeing with the details above - mostly  :grin:

Not all type 1a are quite the same, they need to be normalised, which means taking the width of the light curve to reduce them down to the same thing - see below. They are nearly the same though.

sup1acurve.gif

Also there is some suggestion that some type 1a may be two white dwarfs merging, which means more than 1.4 solar masses and a slightly different curve. Nothing is ever straight forward :smiley:  

I also think to be strict they don't quite reach the Chandrasekhar limit, but go off just before, allowing the degenerate matter to burn, which it does in such a way as to not expand much, so goes off almost all at once.

Nit picking I know... sorry!

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Hi JulianO,

Don't be sorry, that's great thanks, I don't know everything :smiley:. I have heard that many Type 1a's go off just below 1.4Msolar.

Thanks for ironing a few things out :)

Simon

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One of the nicest things about supernova light curves is that they vary with distance in good agreement with Relativity. They are bright enough to be seen at huge distances, therefore at huge recession velocities, and their clocks (what's left of them  :grin: ) tick at a different rate to ours.

This is a splendid read; http://www.amazon.com/The-Supernova-Story-Laurence-Marschall/dp/0691036330

Olly

Clocks???????

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Clocks??????

Unfortunately, the statement "Clocks run at different rates." has one operational definition in special relativity and another, quite different, operational definition in general relativity.

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