Introduction

“Tick, tock, tick, tock.” Clocks help keep us on schedule everyday, but how does our own galaxy keep in time? Pulsar’s are natures very own, “Father Time,” not only do they act as beacons in space, they are the perfect clock.

What makes pulsars’ tick?

Pulsars, or neutron stars, are a very unique type of star. The star is composed of very tightly packed neutrons, that make the density of the star unusually high. Going along with a very dense composition of iron, pulsars have a strong magnetic field. A pulsar’s magnetic field can be between one billion and one quadrillion times stronger than our planet Earth. The north and south poles of a pulsar are from where all their radiation and energy is emitted. Just like a lighthouse, a pulsar beams a very rapid, rotating beam of light in the form of radio waves. When these radio waves are amplified into audible signals via radio telescopes, we hear the constant ticking, just like a clock. The most precisely timed types of pulsars are a subclass called millisecond and recycled pulsars.

What Makes Pulsars Tick? Lauren Teter and Genavieve Trevino (Broadway High School, Broadway, VA)

Pulsar Search Collaboratory

Pulsars signals are periodic, or consistent. A way to help retrieve these signals is a mathematical operation called fourier transform. Fourier transform literally transforms the data from signal vs. time to the form of signal vs. frequency, or how many times something repeats in a given second. Using the fourier transform, we look for signals in the frequency domain (2 Pulses of best profile). In the frequency domain, ‘harmonics’ are naturally occurring at almost every periodic signal. The fundamental or first harmonic is the spin frequency, the second harmonic occurs at twice the frequency of the first harmonic and so on. So, why harmonics? Harmonics, whose growth can be seen in the reduced chi squared, help enhance a pulsar’s signal and help weaker signals become observable. Usually, higher harmonics are preferred for typical pulsar profiles.

Radio Frequency Interference

Opposing pulsars are manmade signals of Earthly origins. These signals can be a curse and a blessing. Most of them can be easily confused with pulsars and thus, they are a curse. Signals that are manmade and interfere with the findings of pulsars are called Radio Frequency Interference or RFI. On the radio spectrum, RFI is present at very similar frequencies as pulsars.

Figure Two: RFI

There several ways that light energy can be converted into sound energy. The demonstration on the table and in figure three is a phototransistor. This Homojunction transistor takes in light at the photo detector (or photocell) and generates pairs of electrons in the base collector junction (capacitor). These hole electron pairs are moved by the transistor’s electric field to the emitter, creating sound.

Homojunction Phototransistors typically have a bandwidth limitation of 250 kHz. This isn’t ideal for recording the sounds of pulsars, because pulsars would cause an emission of gigahertz, or a thousand megahertz.

Figure Three: Homojunction Transistor

Figure Four: GBT

Figure one: Pulsar J1854-1421

In order to listen to these wavelengths, the Green Bank Telescope works as a laser microphone (See Figure Four). It reflects radio waves off of a focal plane panel up to the photo detector in the receiver room of the telescope. The sound that hits the panels causes a bending in a laser beam that is translated into sound and data in the receiver room.

The sound received is where some radio astronomy terminology comes from. If there are radio waves to be refracted up to the receiver, there is data. Sometimes, the sound that results during post-processing and conversion is just background radio emission from space: Noise.

Transforming Light Into Sound

Conclusion

The neutron stars made up of dense iron cores and magnetic fields up to billions of times stronger than Earth’s are called pulars. These pulsars emit jets of light in the form of radio waves; which can be converted into audible signals using a laser microphone as the Green Bank Telescope does. Mathematically, the GBT retrieves signals with the help of an operation called fourier transform. Fourier transform gives information for the frequency domain plot (AKA 2 Pulses of Best Profile). Also in the frequency domain are harmonics, which help enhance a pulsar’s signal. Sometimes, the GBT finds man-made signals called RFI. RFI can be mistaken for a pulsar signal because it can be transmitted at the same frequencies of pulsars.