Calculating Relative Brightness of Type Ia Supernovae

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Discussion Overview

The discussion revolves around the calculation of the "relative brightness" of Type Ia supernovae, particularly in the context of a plot presented by S. Perlmutter. Participants explore how this brightness is determined and its implications for distance measurements in astrophysics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions the meaning of "relative brightness" and how it is calculated, specifically whether it is compared to a special supernova.
  • Another participant explains that Type Ia supernovae are considered "standard candles," implying they are expected to have the same intrinsic brightness, which serves as a reference for comparison.
  • A participant suggests that the brightness of each supernova is compared to a presumed value, leading to a reduction from the observed brightness.
  • There is a mention of a potential logarithmic relationship in the brightness data as indicated by the plot.
  • One participant describes a method of comparing distances estimated from supernovae with those obtained through other methods to calculate brightness.
  • Another participant elaborates on the concept of relative brightness using an analogy involving a light bulb and the inverse square law, emphasizing the unique characteristics of Type Ia supernovae that allow for precise brightness calculations.

Areas of Agreement / Disagreement

Participants express various viewpoints on how relative brightness is determined, with no consensus reached on the specifics of the calculation or the implications of the data presented.

Contextual Notes

Some assumptions regarding the intrinsic brightness of Type Ia supernovae and the methods used for distance estimation remain unaddressed, leading to potential gaps in understanding the calculations involved.

Who May Find This Useful

This discussion may be of interest to those studying astrophysics, particularly in the areas of supernovae, distance measurement techniques, and the use of standard candles in cosmology.

shadishacker
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Dear all,

I am trying to understand the plot below:
http://supernova.lbl.gov/PDFs/expansionhistoryphystoday.pdf
by S.Perlmutter.
However, I don't get the meaning of the "relative brightness" of SN.
How is it calculated?
Is the brightness of each SN compared to a special one?
 
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The type of supernovae studied are thought to be good so-called "standard candles", i.e., they are all expected to have the same brightness. This is what you can compare to.
 
Orodruin said:
The type of supernovae studied are thought to be good so-called "standard candles", i.e., they are all expected to have the same brightness. This is what you can compare to.
So they suppose what value each SN 's brightness should have and then reduce the value from the observed one?!
 
As I can see in the plot, it should be some logarithmic relation. right?
 
The way it's done is to compare distances as estimated by supernovae to distances estimated using other methods. So if we know how far away some supernovae are, we can calculate how bright they are. Then we can use the brightness of other supernovae to estimate how far away they are.
 
The relative brightness is how bright it appears to you. Imagine you are in a dark room, with a single light bulb at some distance away from you. You know that the bulb is putting out 1000 lumens, but your light meter reads 10 lumens, you can use the inverse square law to determine exactly how far away the bulb is.

We can do the same with that very particular type of supernova because of how it works, it slowly accretes mass until it reaches a very specific critical mass and detonates. Astrophysicists have already calculated the critical number and expanding on that using the same laws of physics, you can calculate precisely how bright it much be.
 

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