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

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In summary: Hey brucemitchell,Welcome to PF! You've asked a great question. It's definitely a topic of interest, and one that astronomers are constantly studying. There is no one "magic" number for gamma-ray bursts, as the amount of energy released depends on a number of factors during the star's death.
  • #1
brucemitchell
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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! :)
 
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  • #2
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
 
  • #3
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.
 
  • #4
chroot said:
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... :)
 
  • #5
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.
 
  • #6
Chronos said:
*snip*.

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

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

1A Supernovas, also known as Type Ia Supernovas, occur when a white dwarf star in a binary system accretes enough mass from its companion star to reach a critical mass limit, causing a catastrophic explosion. Since the critical mass limit is the same for all white dwarf stars, the explosion occurs at the same exact point in the star's evolution, resulting in a consistent and predictable explosion point.

2. Is there a specific reason why 1A Supernovas only happen in binary systems?

Yes, 1A Supernovas only occur in binary systems because they require a white dwarf star to accrete mass from its companion star. This process is only possible in binary systems where the two stars are close enough to interact with each other.

3. Can 1A Supernovas occur in any type of galaxy?

Yes, 1A Supernovas can occur in any type of galaxy. They have been observed in both spiral and elliptical galaxies, as well as in dwarf galaxies.

4. Are all 1A Supernovas the same brightness and intensity?

No, not all 1A Supernovas are the same. While they do have a consistent explosion point, the brightness and intensity of the explosion can vary depending on the mass of the white dwarf star and the amount of mass it accretes from its companion star.

5. How do scientists use 1A Supernovas to measure the expansion rate of the universe?

Scientists use 1A Supernovas as a standard candle, meaning they have a known and consistent luminosity. By measuring the brightness of these supernovas, scientists can determine their distance from Earth and use that information to calculate the expansion rate of the universe.

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