If you ever see a radio astronomer wearing headphones, he or she is probably listening to music while overseeing the computer controlling the observations, not what the radio telescope is receiving.
The reason is that almost all cosmic radio sources emit a steady signal that may vary in intensity over months, years, centuries or millennia. What you would hear in the headphones is a steady hiss. The radio astronomer is measuring the properties of the signal responsible for the hiss, and in many cases imaging its source.
For much of the history of radio astronomy, there were only two cosmic radio sources worth listening to: the Sun and the planet Jupiter.
Solar flares produce bursts of radio emission that sound like storms on the seashore. These bursts, called “noise storms,” can be picked up by backyard radio telescopes and enjoyed by amateurs. Jupiter’s radio bursts can be picked up by means of short wave radios. The distant radio sources of interest to professional radio astronomers would just produce a steady hiss in the headphones; not worth listening to apart from when making sure the
system is working, or identifying
interference.
At least, this was the situation until 1967. That was when Jocelyn Bell, a student at Cambridge University, was making observations for a rather unusual project. Just as turbulence in our inhomogeneous atmosphere makes stars twinkle, turbulence and inhomogeneities in the solar wind can make some cosmic radio sources twinkle.
This required the radio telescope she was using to be designed to observe radio emissions that are fluctuating over seconds or less. Around Cambridge, a lot of manmade interference was inevitable, but there was one signal that struck her as odd: sharp pulses of signal recurring every 1.3 seconds, precisely.
Her first thought was this signal was just a bit more manmade interference.
However, over a few days it became clear the signal was coming from space. Not entirely humorously, the source was referred to as LGM-1– that is Little Green Men 1.
Some suggested, maybe light-heartedly, it could be a lighthouse for interstellar travellers. Many more of these sources have been discovered since , and have revealed themselves to be rotating neutron stars emitting beams of radio waves. We see a pulse every time a beam points in our direction. They are not evidence of Little Green Men, however this discovery awoke us to the possibility of rapidly changing radio emissions from deep space.
Pulsars continue sending their pulses for long lengths of time, so they are comparatively easy to search for.
However, in 2007 a radio telescope was pointing in just the right direction to catch a much more elusive event, a Fast Radio Burst (FRB). These last just milliseconds, and if the radio telescope is not pointing in that direction at the time, they are missed. Things changed with the advent of radio telescopes that can observe huge chunks of sky at a time, such as the CHIME radio telescope at our observatory, and the ASKAP radio telescope in Australia. Now thousands of FRB’s have been observed, with a few of them repeating. At this point we have no idea what they are. To be detectable over huge distances the energies involved must be enormous. Neutron stars are a possibility. Little Green Men are not seen as a serious possibility ... yet.
Now, the ASKAP radio telescope has come up with something even weirder. Long, slow pulses that repeat over an hour or so, with some of the pulses being strong, others, weak, and sometimes missing altogether.
It could be some sort of data transmission by those Little Green Men, but the most widely supported idea is that we are looking at a rather odd sort of neutron star.
—————
Jupiter lies low in the dawn glow, Mars a bit higher and to the west, and Saturn a bit higher and further west. The Summer Solstice is on the 20th. The Moon will be Full on the 21st.
Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astrophysical Observatory, Penticton.
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2024-06-18 01:46:00Z
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