Why do 1A Supernovas always explode at the same exact point?

[brucemitchell]

Why do 1A Supernovas always explode at the same exact point?"

Hi. I've had a question lately that I can't seem to find out the answer to. Why do type 1A Supernovae always explode at exactly the same level of mass and energy? I thought that if the
star was more massive, it would be able to "hold off" the explosion for an amount of time because, simply, its more massive and can have more mass taken away, and smaller stars would go sooner...

Also, could anyone that answers this question answer it more in laymans terms? I am only thirteen, I don't exactly know the meaning of any equations or words like "equilibrium"...
Thanks! :)

 

[chroot]

Hey brucemitchell,

Welcome to PF! You've asked a great question. These Type Ia supernovae are used as "standard candles" by astronomers, precisely because they always produce a predictable amount of energy.

It turns out that more-massive stars actually evolve and die faster than less-massive stars. The reason is simple: more massive stars produce more pressure in their cores, and that greater pressure makes the nuclear reactions run faster.

Did you know that most of the stars in the universe are actually binary systems, with two stars orbiting each other, sometimes very closely? Late in these stars' lives, it is possible for one star to begin gradually pulling material from the other. Their orbits decay and the stars become ever closer, and stars get larger as they age. Eventually, one star begins "stealing" material away from its companion.

The "stealing" star becomes more and more massive as it steals from the other. At some point, the "stealing" star becomes too massive to support itself. The core of the star collapses, changing into another, denser form of matter, and that causes an explosion called a Type Ia supernova.

The maximum amount of mass the stealing star can have before it collapses is sort of a hard limit, around 1.44 times the mass of the Sun. It even has a name: the Chandrasekhar limit. Whenever a stealing star's mass crosses that threshold, the collapse and supernova occur quickly. Since every such supernova occurs when a star crosses a specific threshold, every such supernova releases a specific amount of energy.

- Warren

 

[phyzguy]

The idea that all Type1A supernovae have the same energy and brightness is a misconception that comes about from popular science articles calling them "standard candles". It would be more correct to call the "calibratable standard candles". In fact, the peak intrinsic brightness of Type 1A's varies by about 3 magnitudes, which is about a factor of 15 in brightness. In other words, the brightest Type 1A's are about 15 times brighter than the dimmest ones. However, there is a simple relation between the width of the light curve and the peak brightness, called the "Phillips curve", that allows one to determine the peak brightness from the width of the curve. This paper by Phillips first clarified this relation.

So, they don't all explode at the same level of mass and energy.

 

[brucemitchell]

Hey brucemitchell,

Welcome to PF! You've asked a great question. These Type Ia supernovae are used as "standard candles" by astronomers, precisely because they always produce a predictable amount of energy.

It turns out that more-massive stars actually evolve and die faster than less-massive stars. The reason is simple: more massive stars produce more pressure in their cores, and that greater pressure makes the nuclear reactions run faster.

Did you know that most of the stars in the universe are actually binary systems, with two stars orbiting each other, sometimes very closely? Late in these stars' lives, it is possible for one star to begin gradually pulling material from the other. Their orbits decay and the stars become ever closer, and stars get larger as they age. Eventually, one star begins "stealing" material away from its companion.

The "stealing" star becomes more and more massive as it steals from the other. At some point, the "stealing" star becomes too massive to support itself. The core of the star collapses, changing into another, denser form of matter, and that causes an explosion called a Type Ia supernova.

The maximum amount of mass the stealing star can have before it collapses is sort of a hard limit, around 1.44 times the mass of the Sun. It even has a name: the Chandrasekhar limit. Whenever a stealing star's mass crosses that threshold, the collapse and supernova occur quickly. Since every such supernova occurs when a star crosses a specific threshold, every such supernova releases a specific amount of energy.

- Warren

Ok, thanks for the answer! I appreciate it... also, its there a threshold for gamma-ray bursts in stars, or does it depend on other factors during the stars death? Its off topic from the OP, I know, but it does involve supernovae... :)

 

[Chronos]

Just to clarify, the progenitor star of an SN1a is believed to be a white dwarf that accretes mass from a companion star. Most white dwarfs are composed of degenerate [highly compressed] carbon and oxygen. Carbon and oxygen are fusible, but, white dwarfs are not massive enough to achieve the necessary temperature. Once the white dwarf reaches a mass of about 1.38 solar, it achieves the temperature required to initiate carbon fusion and that's where the fun begins. It can, however, take a thousand years or more for this process to go out of control and result in a supernova detonation. A white dwarf cannot regulate itself like a normal star because of the degenerate nature of its composition. Another possible route to a SN1a is called the double degenerate model. Under this scenario two white dwarfs merge, thereby reaching the mass necessary to trigger carbon fusion. The uncertainty of the masses involved is believed to account for why some SN1a are brighter than others. This model has been gaining favor over the past decade.

The processes involved in GRB's are essentially unknown. They tend to be at great distances and of brief duration - rarely more than a minute or so. They are divided into two classes, short and long. As the name implies, a short GRB only lasts for a couple of seconds while a long GRB lasts longer - typically 30 seconds to several minutes. The two classes are believed to result from different processes. One hypothesis for long GRB's is they involve massive stars that suffer an unusually catastrophic kind of core collapse event. It has been suggested the progenitor star may be a pop I, or extremely metal deficient. For short GRB's we mostly have little more than guesses. The typical distance and short duration of all GRB's makes them difficult to study.

 

[brucemitchell]

*snip*.

Ok, it took me a while and a dictionary, but I think I understand now. Thanks.