Children, gather round. I hope you’re sitting comfortably because it’s time for another of Harvey’s storytime posts. Lean back on a deckchair and take your eyes to the skies. This week, we’re exploring the hidden wonders of the universe.
A few weeks ago, myself and Yanhao partook on a school trip to a little place called Jodrell Bank. There rests one of the world’s largest radio telescopes – the Lovell Telescope, a whopping 76.2m in diameter. Now, you may be wondering, “Why do they need a 76.2m diameter telescope to listen to Classic FM? Is the sound quality really that much better?”. The answer is yes, the sound quality is a lot better, but fortunately that’s not what scientists are using the telescope for. No, at Jodrell Bank, they’re listening out for the music of the cosmos…
Just as we use regular optical telescopes to observe ‘visible’ objects in space, we require radio telescopes to study the radio frequency portion of the electromagnetic spectrum emitted by astronomical objects. The reason you’ve never seen a portable radio telescope before is because they need to be much larger than optical telescopes in order to retain the same amount of resolution. The following equation describes the relationship between the resolving power, θ, of the telescope, its diameter, D, and the wavelength of light it is observing, λ:
θ = λ / D
The smaller the value of θ, the greater the ability of the telescope to determine between two faraway objects. Radio wavelengths are much longer than that of visible light, so we need to massively increase the diameter in order to compensate. Another way of achieving the same effect is to combine multiple smaller telescopes into an array. An example of this is the Very Large Array (I know, scientists are really creative) in New Mexico, which culminates data from a cluster of small telescopes arranged in a Y shape spanning 36km into a single recognisable interference pattern.
In almost every other aspect, radio telescopes are just the same as the ones we looked at last week. The other main difference is that radio telescopes can be used at anytime of day and at any location, since radio waves are not affected by atmospheric conditions or lighting. However, since they are highly sensitive to sources of radio waves, electronic devices like mobile phones must be kept switched off on site. At Jodrell Bank, the telescope is so sensitive that even the microwave in the staff tea room is shielded inside a metal box to prevent interference.
So what exactly does the Lovell Telescope look at?
A better question would in fact be, what does the Lovell Telescope not look at? Actually, maybe it wouldn’t. Nevermind, my point is that radio telescopes get to look at a bunch of really cool stuff. One example of a radio-emitting object in space is a pulsar, which we learnt about on our day trip. These are pulsating-stars that emit a strong beam of electromagnetic radiation along an axis which spins at a regular interval. When this beam coincides with us on the Earth, we can detect the radio waves given off. If you imagine the beam sweeping around and around, illuminating the Earth once a rotation, they’re kind of like the lighthouses of the universe. The first pulsar to be discovered was the Crab Pulsar, located at the centre of the Crab Nebula, which is the remnant of a supernova.
It honestly looks nothing like a crab, but you can’t deny that it looks spectacularly pretty. The fastest spinning pulsar to have been discovered spins 716 times a second, and has the really catchy name of PSR J1748-2446ad.
So next time you find yourself lost in space, be rest assured by the fact that the pulsars will always guide you slightly further away from home.