<p>This is really about the nature of physical theories - we have observational evidence and a (falsifiable) theory has been posited to explain what is happening. The evidence since that theory was posited has served to reinforce its claims to correctness.</p>

<p>(But all magnets we have observed are dipoles - in theory monopoles exist but have never been observed. But no theory has been posited that neutron stars are monopoles - the energy required to create such a monopole would, I am sure, but even greater than that released in a supernova.)</p>

CC BY-SA 4.0
2020-05-06T23:36:27.943Z
I think that by itself this argument isn't enough; the question asks about *two beams* not two poles. Also a magnetic field can have a more complex shape than a pure dipole.. Just for example; [The hot spots are presumed to be the termination of the active magnetic field lines, so there is really no magnetic "axis". The field is more complicated.](https://astronomy.stackexchange.com/a/36080/7982)
uhoh
CC BY-SA 4.0
2020-05-06T10:08:34.617Z
2020-05-06T10:08:34.617Z
adrianmcmenamin
<p>The magnetic and rotational axes don't have to be <em>exactly</em> at 90 degrees to each other to see both beams. They only need be approximately at 90 degrees (depending on the 'opening angle' of the emission cone).</p>

<p>So there are plenty of pulsars that satisfy this and have two peaks in their profiles (when we observe their emission) that are approximately half a spin period apart. Each peak looks different to the other, so the best guess currently is that we are seeing the beam from one pole and then the other.  </p>

CC BY-SA 4.0
2020-05-08T19:48:23.547Z
2020-05-08T20:10:29.967Z
2020-05-08T20:10:29.967Z
user1551817
<p>Pulsars are neutron stars the emit a beam of electromagnetic radiation that is not aligned with their rotation axis. So we can only see a neutron star as a pulsar if the beam crosses Earth's path. </p>

<p><a href="https://i.sstatic.net/IdWiA.png" rel="noreferrer"><img src="https://i.sstatic.net/IdWiA.png" alt="enter image description here"></a></p>

<p>The common representation is that there are two beams, one on each side, but unless the magnetic axis and the rotation axis are at 90°, we can only ever see one of the two beams. How do we know that there are two beams and not one, or four, or any other number?</p>

<pulsar>
How do we know pulsars have two beams?
usernumber
# How do we know pulsars have two beams?

(Asked by: username_0 on 2020-05-06)

Pulsars are neutron stars the emit a beam of electromagnetic radiation that is not aligned with their rotation axis. So we can only see a neutron star as a pulsar if the beam crosses Earth's path.

[![enter image description here](https://i.sstatic.net/IdWiA.png)](https://i.sstatic.net/IdWiA.png)

The common representation is that there are two beams, one on each side, but unless the magnetic axis and the rotation axis are at 90°, we can only ever see one of the two beams. How do we know that there are two beams and not one, or four, or any other number?

**Tags:** pulsar


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## 2 answers

### Answer by username_3 on 2020-05-08. Score: 4 | Accepted answer

The magnetic and rotational axes don't have to be *exactly* at 90 degrees to each other to see both beams. They only need be approximately at 90 degrees (depending on the 'opening angle' of the emission cone).

So there are plenty of pulsars that satisfy this and have two peaks in their profiles (when we observe their emission) that are approximately half a spin period apart. Each peak looks different to the other, so the best guess currently is that we are seeing the beam from one pole and then the other.


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### Answer by username_1 on 2020-05-06. Score: 2

This is really about the nature of physical theories - we have observational evidence and a (falsifiable) theory has been posited to explain what is happening. The evidence since that theory was posited has served to reinforce its claims to correctness.

(But all magnets we have observed are dipoles - in theory monopoles exist but have never been observed. But no theory has been posited that neutron stars are monopoles - the energy required to create such a monopole would, I am sure, but even greater than that released in a supernova.)

> **Comments:**
> **username_2**: I think that by itself this argument isn't enough; the question asks about *two beams* not two poles. Also a magnetic field can have a more complex shape than a pure dipole.. Just for example; [The hot spots are presumed to be the termination of the active magnetic field lines, so there is really no magnetic "axis". The field is more complicated.](https://astronomy.stackexchange.com/a/36080/7982)  

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