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From my understanding of pulsars, pulsars do not produce sound, but radio telescopes can record the radio waves they emit, which can be interpreted as sound. The radio waves are electromagnetic waves, similar to light, not sound. The waves are beamed out along the pulsar's magnetic poles, and the Earth receives pulses of radiation as the beam crosses.

However, this means that this is not the sound of pulsars and it's just the interpretation from our side and how our machinery detects it and interprets it for our understanding. The first recording of pulsars recorded a "thumping" or "knocking" sound by our machinery.

My question is does pulsar stars have their own sound coming out of them? Is it the same "thumping" sound that we captured? Please clarify this.

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Ganit
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Sound is the vibration of matter. Sound can only travel in a medium like air or water. So no sound can come across space. Pulsars do have a very shallow atmosphere, but it is only a few microns deep (according to some models)

The cause of the pulsing is the rotation of the star. It is constantly putting out energy in two beams, but these rotate with the star and we detect the pulses as the beam regularly passes us.

But it is totally reasonable to convert the radio waves that do travel across space to sound. Humans are not naturally able to sense radio waves (ems individuals notwithstanding) so the radio waves would have to be converted into something that might be a graph (like the one used on the Joy Division album) or it might be an image, but to allow humans to get a sense of what the radio signal is like, sound is a very natural choice.

It sounds like a "knocking" because each pulse is quite sharply defined along the time axis, but contains a mix of radio frequencies. So this sound is meaningful, not arbitrary. Like a terrestrial radio station, no sound actually travels from the station to your radio. But unlike a radio station, the source of the radio waves is not a sound that has been changed to an electrical signal by a microphone, nor any natural analogue of that.

isaacg
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James K
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  • So if anyone says that pulsars have a knocking sound, it's not true right? It's just the conversion of radio waves into something that we can understand right? – Ganit Mar 25 '24 at 09:02
  • Welll ... see my last paragraph. The sound is not arbitrary. But obviously, no sound actually travels across space. Pulsars emit constantly but in rotating beams of em energy. – James K Mar 25 '24 at 09:04
  • I understand that this sound is meaningful for our understanding and study of pulsars. But this sound came out of our machinery while detecting the radio waves and could not have come from the origin source of pulsars. – Ganit Mar 25 '24 at 09:06
  • Also, one spinoff question, let's say if we intercept those radio waves in outer space i.e. outside the earth's atmosphere, then would there be any difference in the "sound" produced by the same machinery? I am asking this because I think the earth's atmosphere may attenuate the radio waves coming and hence the results could vary. – Ganit Mar 25 '24 at 09:09
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    You seem to be trying to prove some point. Of course, no sound travels through space. But the conversion to sound is not arbitrary. This is a meaningful conversion. see my last (edited) paragraph The atmosphere is transparent to radio waves, so there is not much attenuation. – James K Mar 25 '24 at 09:09
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    @Ganit Almost all astronomy data outside of an actual optical telescope is "just" a conversion of something we can't sense into something we can. We convert infrared light into visible light, we convert radio into images or sounds or columns of numbers. Our senses are made to function in the very limited realm of the Earth's surface, and beyond that realm we have to convert the data. A pulsar doesn't make a sound as such, but it emits energy, and playing back that emission as a sound wave is no more false than charting it on a graph. It's all just interpretations of the received signal. – Darth Pseudonym Mar 25 '24 at 20:28
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    "it is totally reasonable to convert the radio waves that do travel across space to sound" – And, of course, AM radios do just that, all the time. – Jörg W Mittag Mar 25 '24 at 23:36
  • @DarthPseudonym Even optical telescopes use color filters to produce a sort of conversion, unless you are looking through the eyepiece directly. That conversion can be meant to simulate the 'natural' colors as closely as possible, but they do that by combining red, green, and blue intensities to stimulate the sensors in our eyes instead of the continuous spectrum that exists in reality. – Jason Goemaat Mar 26 '24 at 15:49
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    Minor point: sound can transmit in interstellar space, but only wavelengths much longer than the mean free path of particles in the interstellar medium, which is of order AU, unfortunately larger than pulsars and people. – Sten Mar 26 '24 at 17:08
  • @sten, I suppose you are thinking of things like supernova shock waves. I can find lots of reference to shocks in the ISM, not so much about linear compression waves, though I suppose even supernova shocks must become more linear over time. I might ask a question about that. --- Turns out https://astronomy.stackexchange.com/questions/17838/are-there-any-sounds-in-space – James K Mar 27 '24 at 08:32
  • Yeah that link is closer to what I'm referring to. I'm just considering the known density of the warm interstellar medium (of order 1 hydrogen atom per cm^3) and the $H$-$H$ and $H$-$H^+$ scattering cross sections. – Sten Mar 27 '24 at 19:47
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My question is does pulsar stars have their own sound coming out of them? Is it the same "thumping" sound that we captured?

Those audio recordings result from transforming the signals received via electromagnetic devices (telescopes) into sound. Sonification has become a widely used scientific approach for communicating and understanding data of all kinds. The linked article describes why. Quoting from the authors (emphasis mine),

Compared to vision, the ear is better at perceiving time-based information, patterns and transient changes and does not require us to be oriented in the direction of the sound. Furthermore, hearing is always active, which makes it useful for monitoring alarms and continuous data streams, whereas an event may be missed with visual inspection due to blinking or looking away momentarily. An effective example of audible inspection of data used in the scientific context is the Geiger Counter, which clicks in response to invisible radiation levels. Therefore, sound has the potential to be a more effective alternative to visualisation for exploring time-series data and for live data monitoring of transient events whilst occupied with different tasks.

So the "sounds" of pulsars that are presented on many websites are not pulsar sounds per se. They are data recorded by telescopes (which receive data using electromagnetism) that have been transformed to sound. Geiger counters were developed about 100 years ago. The radioactive decays they detect are not sound. The clicks emitted by a Geiger counter are a form of sonification, as are the "sounds" of a pulsar.

David Hammen
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    Sonification can even be used for sound. The ultrasonic chirps of bats and the subsonic songs of whales have been transformed in frequency so that we humans can hear those sounds. – David Hammen Mar 26 '24 at 15:55
  • Thanks for the explanation. – Ganit Mar 26 '24 at 17:35
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    Surely there are mechanical vibrations over a huge range of frequencies in a pulsar. However, it's rather tricky getting close to a pulsar with a stethoscope. ;) As you approach it, you tend to get spaghettified, assuming you don't get vaporised by the heat and radiation. And when you land on it, the gravity tends to squish you into an atom-thick paste. – PM 2Ring Mar 26 '24 at 17:47
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Space has no sound since it has no air as James K said, and sonification does exist, as David Hammen said. Theoretically, if you somehow took a pulsar and put it into an atmosphere of air, then there would be sound. You (and everyone else) would also probably die due to it's gravity and radiation, sadly.

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