Use of Standard Candles in Measuring Distances in Astronomy

[MatinSAR]

TL;DR Summary: I need to understand their definition.

In a refrence I've read :
One of the basic missions of Astronomy is to measure distances in the cosmos. This is usually done using the method of standard candles, which requires identifying astronomical objects or phenomena with a repeatable luminosity, and to measure that luminosity.

Could I describe a standard candle as a celestial object with known luminosity? Even if its luminosity varies over time, we understand how it changes. Am I right?

 

[Ibix]

I would keep in mind that it's a chain of observations standing one atop another, so I'd tend to go with things where we believe we know the luminosity. But basically, yes you are correct. Since we can measure the amount of light we receive from each one and we believe we know how much light they emit, we can use the ratio to calculate the luminosity distance.

 

[MatinSAR]

@Ibix Thank you.

 

[MatinSAR]

Hi everyone,
I'm currently preparing a presentation on the use of standard candles for measuring distances in astronomy. I'm looking for some references that can help deepen my understanding of this topic. Could you please recommend any books, papers, or articles that you found useful?
I'm looking for undergraduate-level references, so I prefer not to have highly specialized sources.
Thank you for your assistance!

 

[DaveC426913]

Even if its luminosity varies over time,

You mean like Cepheid Variables?

 

[MatinSAR]

You mean like Cepheid Variables?

Yes.

 

[MatinSAR]

One more question.

which requires identifying astronomical objects or phenomena with a repeatable luminosity, and to measure that luminosity.

By "repeatable luminosity," we mean that an object's luminosity can be inferred by comparing it to other similar objects with known luminosities, for example, those with similar spectral characteristics. Am I right?
e.g. when we use stars as a standard candle ...

 

[DaveC426913]

One more question.

By "repeatable luminosity," we mean that an object's luminosity can be inferred by comparing it to other similar objects with known luminosities, for example, those with similar spectral characteristics. Am I right?
e.g. when we use stars as a standard candle ...

But how do you know they are "similar objects"?

Is having "similar spectral characteristics" sufficient to infer that they have similar luminosities? And to what degree of confidence?

The reason Cepheid Variables are useful is because we have an independent way (independent of their apparent mag) of judging their absolute magnitude.

 

[MatinSAR]

But how do you know they are "similar objects"?

Is having "similar spectral characteristics" sufficient to infer that they have similar luminosities? And to what degree of confidence?

That's what I'm trying to find out. I was questioning what they meant by "repeatable luminosity," and that similar spectral characteristics was my guess. So I don't know the answer to your question.

 

[DaveC426913]

That's what I'm trying to find out. I was questioning what they meant by "repeatable luminosity," and that similar spectral characteristics was my guess. So I don't know the answer to your question.

Oh right. This is from a reference. Can you quote from the reference?

 

[MatinSAR]

Oh right. This is from a reference. Can you quote from the reference?

Sure.

Picture from Astronomy at the Frontiers of Science.

 

[berkeman]

The reason Cepheid Variables are useful is because we have an independent way (independent of their apparent mag) of judging their absolute magnitude.

More recent work has used supernovae for standard candles at further distances, which helped lead to discoveries about Dark Energy and the accelerated expansion of the Universe.

I attended a lecture by a prominent physicist a couple years ago (I wish I could remember his name) where he talked about all of the work that had happened in recent years by groups working on studying the expansion of the Universe and how Dark Energy is causing an acceleration of that on large scales. They had come up with some new standard candles to let them more accurately measure the redshift of deep space objects and galaxies, and from that were able to prove that the expansion is speeding up.

Here is one page with information about that work: https://science.nasa.gov/universe/t...energy-is-responsible-so-what-is-dark-energy/

Expansion is Speeding Up, Supernovae Show

Scientists previously thought that the universe's expansion would likely be slowed down by gravity over time, an expectation backed by Einstein's theory of general relativity. But in 1998, everything changed when two different teams of astronomers observing far-off supernovae noticed that (at a certain redshift) the stellar explosions were dimmer than expected. These groups were led by astronomers Adam Riess, Saul Perlmutter, and Brian Schmidt. This trio won the 2011 Nobel Prize in Physics for this work.

While dim supernovae might not seem like a major find, these astronomers were looking at Type 1a supernovae, which are known to have a certain level of luminosity. So they knew that there must be another factor making these objects appear dimmer. Scientists can determine distance (and speed) using an objects' brightness, and dimmer objects are typically farther away (though surrounding dust and other factors can cause an object to dim).

This led the scientists to conclude that these supernovae were just much farther away than they expected by looking at their redshifts.

Using the objects’ brightness, the researchers determined the distance of these supernovae. And using the spectrum, they were able to figure out the objects’ redshift and, therefore, how fast they were moving away from us. They found that the supernovae were not as close as expected, meaning they had traveled farther away from us faster than ancitipated. These observations led scientists to ultimately conclude that the universe itself must be expanding faster over time.

 

[phyzguy]

It's not just the spectral type that allows us to recognize Cepheid variables. They have very distinctive light curves. See the light curve of Delta Cephei here.