I've watched a video on youtube about neutron stars as called (pulsar) and it claims that pulsars produce this sound. then i found that they produce radio waves which can be converted to sound. Radio waves are electro-magnetic waves and sound is a mechanical wave which of course can't be transmitted in vacuum.
My question is, do they "really" produce sound that is then converted somehow in space as radio waves or do they just just create radio waves which humans convert to sound?
Stars can produce "sound" when they pulsate. Stellar oscillations produce waves of density and or pressure that propagate within the star.
These sound waves cannot travel to us through space because the near vacuum does not allow them to propagate.
Sound waves due to stellar oscillations can be detected by looking for periodic signals in a star's brightness as it pulsates, or by detecting the motion of the stellar surface towards and away from us using the Doppler effect.
Because the characteristic frequencies tell us something about the stellar interior, this branch of science is termed asteroseismology.
The frequencies detected can be converted back into sounds we can hear in exactly the same way that any electrical signal can in a radio or HiFi.
The characteristic frequencies have an order of magnitude given by $\sqrt{G \rho}$, where $\rho$ is the average density of the star.
For the Sun, this corresponds to $3\times 10^{-4}$ Hz (or a period of 50 minutes). The dominant frequency turns out to be a bit faster, with a period of 5 minutes. So you would indeed need to bump this frequency up by factors of 42,000 to make an audible signal.
The equivalent calculation for pulsars (neutron stars), which have densities of order a few $10^{17}$ kg/m$^3$, suggest characteristic frequencies of 5 kHz. A few pulsars do have a signal frequency of this order (the millisecond pulsars), however most pulsars are much slower, with frequencies of about 1 Hz.
It was quickly realised that pulsations are not responsible for the pulsar phenomenon. Pulsars are rapidly rotating neutron stars and it is rotational modulation of their electromagnetic radiation that gives the signal its frequency. The range of pulsar rotation periods is responsible for the range of signal frequencies found.
The pulsar signal is often transformed directly into a voltage and then into an audible signal by feeding it to a loudspeaker.
