Radio waves surround us everywhere. All natural radio signals are created by moving charged particles.
Space objects produce radio signals – planets and stars emit radio waves which can be converted to sound recordings.
Processes by which astronomical bodies emit radio waves:
- thermal radiation from solid bodies
- thermal (bremsstrahlung) radiation from hot gas in the interstellar medium
- synchrotron radiation from relativistic electrons in weak magnetic fields
- spectral line radiation from atomic and molecular transitions occurring in the interstellar medium or in the gaseous envelopes around stars
- pulsed radiation from fast-spinning neutron stars with strong magnetic fields
Electromagnetic waves can travel through space without a medium. In a vacuum, electromagnetic radiation propagates at the speed of light.
Sound wave is a mechanical wave. Such wave is unable to travel through a vacuum. However, only few regions in space are perfect vacuum. There is a matter in space between the stars and galaxies. Atoms of gas give the universe some sort of atmosphere, albeit a very thin one – but still, it is a medium through which sound waves can be carried. Interestingly, not all notes can be transmitted. In the interstellar medium, where the particles are widely spaced, only very long wavelength / low-frequency sounds can be carried.
Our Sun is a big sphere of turbulent hot plasma. The continual turbulent convection motions inside the star set up vibrations. Although these vibrations of the Sun are genuine sounds, their frequencies are far too low for a human to hear, and they can be made audible only by speeding them up approx. 42,000 times.
The source of most VLF emissions on Earth is lightning. Lightning strokes emit a broadband pulse of radio waves, just as they unleash a visible flash of light.
The moving charged particles that create the northern lights also produce intense radio emission at very low frequencies.
Most of Jupiter’s radio emissions are caused by electron synchrotron emission in Jupiter’s magnetic field, which is much stronger than that of Earth. This magnetic field traps fast moving electrons, creating radio waves.
The interaction of Jupiter and his orbiting moon Io creates so called Jupiter bursts, which are of a low radio frequency.
Jovian chorus is generated in Jupiter’s radiation belts by electrons spiraling along planet’s magnetic field lines.
Jovian whistlers are generated by lightning discharges in the atmosphere of Jupiter.
Jovian electron cyclotron emissions are generated by energetic electrons spiraling along the magnetic field lines of Jupiter and its magnetized moons.
Jovian bow shock is similar to a sonic boom made by a supersonic jet flying through Earth’s atmosphere, except that the bow shock is caused by the supersonic solar wind being diverted around Jupiter’s magnetic field; the solar wind is heated, slowed and deflected.
Saturn, like other magnetised planets, is a source of intense radio waves, which are transmitted into space from the planet’s polar regions. These emissions are called Saturn kilometric radiation and they are closely related to Saturn’s auroras.
Pulsars are rapidly spinning neutron stars. Their powerful magnetic fields lead to radio pulses that can be detected on Earth each time they rotate – this is called the “lighthouse effect”. For every detected pulse, the pulsar has revolved around its axis once.
The Vela pulsar is located near the center of the Vela supernova remnant, resulting from the supernova that exploded 10,000 years ago. The pulsar is the collapsed core of this star. It rotates with a period of 89,3 milliseconds.
Black holes are even more gravitationally-collapsed masses than neutron stars.