<p>The spectrum of a star is almost certainly a unique fingerprint. Even though stars are born in clusters, formed from the reasonably chemically homogeneous environment of a giant molecular cloud, there are likely to be <em>small</em> differences in their local environment. Furthermore their formation environments, and the stars themselves at later times, can be polluted by external events (e.g. nearby supernovae). Even if their chemical abundances were identical, their spectra would not be because of differences in their mass, rotation and hence their temperatures.</p>

<p><strong>But</strong>, the differences between stars may be smaller than the measurement precision, rendering their spectra effectively indistinguishable.</p>

<p>To give any sort of definitive answer requires some definition of what types of stars are being observed, their temperature, gravity and chemical abundance dispersion, at what spectral resolution and with what signal to noise ratio in what waveband.</p>

<p>At the moment I would say this is <em>impossible</em> for any star in our Galaxy. The differences in the spectra between one star and its most similar "twin" (the word might be appropriate here, as they were likely born in the same stellar nursery) are <em>far</em> smaller than we can distinguish with current data and techniques.</p>

CC BY-SA 4.0
2017-12-23T23:29:18.593Z
2018-12-19T07:17:18.983Z
2018-12-19T07:17:18.983Z
ProfRob
<p>Even the optical spectrum alone has lots of goodies. </p>

<p>In addition to <a href="https://en.wikipedia.org/wiki/Astronomical_spectroscopy#Temperature_and_size" rel="nofollow noreferrer">chemical abundance, size, and other outer properties from emission and absorption lines</a> you can get the rotational rate from a narrow line's doppler profile, and very careful spectroscopy <a href="https://arxiv.org/abs/0811.2908" rel="nofollow noreferrer">information on vibrational modes</a> of the star through spectral <a href="https://en.wikipedia.org/wiki/asteroseismology" rel="nofollow noreferrer">asteroseismology</a>.</p>

<p>Also most stars are part of multiple-star systems, so spectroscopy from a distance will yield information on <em>each star</em> and so even if two different stars are barely differentiable, chances are that their companions won't be also! This also gives some potential additional differentiation from the relative velocities, but that depends on how long you observe and if you know the orientation.</p>

CC BY-SA 4.0
2018-12-20T08:52:43.107Z
2018-12-20T08:52:43.107Z
uhoh
<p>By using only the electromagnetic signature of a star, could a star be distinguished with reliable accuracy from any other star?<br>
To elaborate a little, say we have a collection of about 200,000 stars. By using EM spectrum alone (and any means of analysis, such as spectral analysis), and by tagging each star with its corresponding EM signature, could there be similarities too close to fail a distinction between any two or more stars?  </p>

<p>Now, of course, I know that such a thing is possible. I'm not asking whether it is possible. I just want to know the odds of such a lack of distinction, considering all the factors of stellar evolution. It's either in the ballpark or not.</p>

CC BY-SA 3.0
2017-12-23T22:48:03.453Z
I don't understand. You ask if two stars could be indistinguishable. Then you say that you know that any two stars are distinguishable. Then you ask what are the odds of two stars not being distinguishable. Then you ask for an estimation of something ("in the ballpark"). The question is confused and unclear.
James K
CC BY-SA 3.0
2017-12-23T23:21:18.433Z
@JamesK Given enough time, virtually anything should hypothetically possible. That is what I meant by "such a thing is possible." The ballpark I mention is the reliability factor. Is the distinction between two stellar spectra accurate and this reliable? Where reliability breaks down, so does distinction. By including the last paragraph, I was simply trying to remove any obvious answers such as the answer I made in the first sentence of this comment. Realistically, given real world circumstances, is such a similarity possible, or do factors involved in, say, stellar evolution, prevent it?
BenjaminF
CC BY-SA 3.0
2017-12-24T08:25:05.000Z
*Given enough time, virtually anything should [be] hypothetically possible*  This is not how science works.  Some things will remain impossible no matter how long you spend trying to do it.
StephenG - Help Ukraine
<spectroscopy><stellar-evolution><stellar-structure><spectral-type>
Stellar electromagnetic signatures
BenjaminF
# Stellar electromagnetic signatures

(Asked by: username_0 on 2017-12-23)

By using only the electromagnetic signature of a star, could a star be distinguished with reliable accuracy from any other star?  
To elaborate a little, say we have a collection of about 200,000 stars. By using EM spectrum alone (and any means of analysis, such as spectral analysis), and by tagging each star with its corresponding EM signature, could there be similarities too close to fail a distinction between any two or more stars?

Now, of course, I know that such a thing is possible. I'm not asking whether it is possible. I just want to know the odds of such a lack of distinction, considering all the factors of stellar evolution. It's either in the ballpark or not.

**Tags:** spectroscopy, stellar-evolution, stellar-structure, spectral-type

> **Comments:**
> **username_1**: I don't understand. You ask if two stars could be indistinguishable. Then you say that you know that any two stars are distinguishable. Then you ask what are the odds of two stars not being distinguishable. Then you ask for an estimation of something ("in the ballpark"). The question is confused and unclear.  
> **username_0**: @username_1 Given enough time, virtually anything should hypothetically possible. That is what I meant by "such a thing is possible." The ballpark I mention is the reliability factor. Is the distinction between two stellar spectra accurate and this reliable? Where reliability breaks down, so does distinction. By including the last paragraph, I was simply trying to remove any obvious answers such as the answer I made in the first sentence of this comment. Realistically, given real world circumstances, is such a similarity possible, or do factors involved in, say, stellar evolution, prevent it?  
> **username_2**: *Given enough time, virtually anything should [be] hypothetically possible*  This is not how science works.  Some things will remain impossible no matter how long you spend trying to do it.  

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## 2 answers

### Answer by username_3 on 2017-12-23. Score: 3 | Accepted answer

The spectrum of a star is almost certainly a unique fingerprint. Even though stars are born in clusters, formed from the reasonably chemically homogeneous environment of a giant molecular cloud, there are likely to be *small* differences in their local environment. Furthermore their formation environments, and the stars themselves at later times, can be polluted by external events (e.g. nearby supernovae). Even if their chemical abundances were identical, their spectra would not be because of differences in their mass, rotation and hence their temperatures.

**But**, the differences between stars may be smaller than the measurement precision, rendering their spectra effectively indistinguishable.

To give any sort of definitive answer requires some definition of what types of stars are being observed, their temperature, gravity and chemical abundance dispersion, at what spectral resolution and with what signal to noise ratio in what waveband.

At the moment I would say this is *impossible* for any star in our Galaxy. The differences in the spectra between one star and its most similar "twin" (the word might be appropriate here, as they were likely born in the same stellar nursery) are *far* smaller than we can distinguish with current data and techniques.


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### Answer by username_4 on 2018-12-20. Score: 2

Even the optical spectrum alone has lots of goodies.

In addition to [chemical abundance, size, and other outer properties from emission and absorption lines](https://en.wikipedia.org/wiki/Astronomical_spectroscopy#Temperature_and_size) you can get the rotational rate from a narrow line's doppler profile, and very careful spectroscopy [information on vibrational modes](https://arxiv.org/abs/0811.2908) of the star through spectral [asteroseismology](https://en.wikipedia.org/wiki/asteroseismology).

Also most stars are part of multiple-star systems, so spectroscopy from a distance will yield information on *each star* and so even if two different stars are barely differentiable, chances are that their companions won't be also! This also gives some potential additional differentiation from the relative velocities, but that depends on how long you observe and if you know the orientation.


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