OSB archive
OSB archive

LOFAR tunes in to pulsars

Pete Wilton

A field in Chilbolton, Hampshire, could help unlock the secrets of peculiar rotating neutron stars known as pulsars.

It's here that an international team, including Oxford University scientists, are building an array that, linked up with stations in the Netherlands, Germany, and France will form LOFAR, one of the world's most powerful radio telescopes.

I asked LOFAR scientist Aris Karastergiou of Oxford's Department of Physics about the new telescope, the search for pulsars, and how games console hardware could help decode their enigmatic signals...

OxSciBlog: What makes pulsars so challenging to study?
Aris Karastergiou: In a sense it is amazing that we can study pulsars at all, as they are compact objects around 10-20 km in diameter. However, they emit very bright beams of light (in the radio frequencies) from their two magnetic poles, which sweep through space as the pulsar rotates.

If Earth happens to be in the path of these sweeping beams of a pulsar, we can point a radio telescope towards it and collect this light. Even then, however, the fact that the most scientifically interesting pulsars rotate over 100 times a second means that observations require not only high sensitivity but also very fast recorders, capable of sampling the incoming light at extremely short intervals.

The fact that pulsar light travels through the Galaxy before reaching us adds further challenges to pulsar studies, as radio waves interact with electrons in the medium between the stars.

OSB: What is LOFAR and how can it help with these studies?
AK: LOFAR (the Low Frequency Array) is a brand new telescope, made up of a large number of receiving elements organised in so-called stations. The core of this telescope is located in the Netherlands, while outer stations are located in Germany, France, the UK and elsewhere. Unlike other radio telescopes, LOFAR is not made up of parabolic reflectors (like satellite dishes), but of little radio antennas.

To point the telescope at a star in the sky, we electronically combine the signals from these antennas with a certain set of time delays LOFAR is a very sensitive telescope and we expect to discover a large number of new pulsars by surveying the northern sky. Compared to the existing giant radio telescopes, pulsars are brighter at LOFAR radio frequencies.

Observing at low frequencies will give us better understanding of the radio emission mechanism, and also shed light on the physical processes associated with the propagation of pulsar light through our Galaxy.

OSB: What difference will the new Chilbolton facility make?
AK: Each of the international LOFAR stations, including Chilbolton, contributes to LOFAR by increasing the capability to tell apart objects in the sky that appear very near to each other. If we imagine that LOFAR can take photographs of the sky, the most distant stations are necessary to reduce the pixel size and make images of greater detail.

On the other hand, the international LOFAR stations are very sensitive telescopes in their own right and can be used independently from LOFAR. They can observe large fields in the sky with large sensitivity and very fast sampling of the incoming radiation, making them very useful instruments for searches of bursty signals like giant radio pulses from pulsars.

We are enhancing the LOFAR station at Chilbolton to take full advantage of these capabilities, and we aim to transform it into a fantastic instrument of discovery.

OSB: How does the sort of hardware found in games consoles help you analyse signals?
AK: Modern games consoles use very powerful graphics processors to deliver stunning images and animation. The secret behind this lies in the enormous computing power of these processors at performing certain simple calculations in parallel. When searching for bright, short duration radio pulses of astronomical origin, we need to counter the effects of propagation of light through the Galaxy. This process involves a simple, repetitive algorithm that can be easily run in parallel on graphics processors.

We are currently building a computer cluster based on graphics processing units, which will be capable of performing a real-time search for bright, short duration astrophysical radio pulses in the data from the Chilbolton station.

Dr Aris Karastergiou is based at Oxford University's Department of Physics where he is a Leverhulme Early Career Fellow.