APOD and General Astronomy Discussion Forum
https://asterisk.apod.com/
A radio telescope located in outback Western Australia has observed a cosmic phenomenon with a striking resemblance to a jellyfish. ...A composite image of the USS Jellyfish in Abell 2877 showing the optical Digitised Sky
Survey (background) with XMM X-ray data (magenta overlay) and MWA 118 MHz radio
data (red-yellow overlay). Credit: Torrance Hodgson, ICRAR/Curtin University.
“We looked at the data, and as we turned down the frequency, we saw a ghostly jellyfish-like structure begin to emerge,” he said. “This radio jellyfish holds a world record of sorts. Whilst it’s bright at regular FM radio frequencies, at 200 MHz the emission all but disappears. No other extragalactic emission like this has been observed to disappear anywhere near so rapidly.”
This uniquely steep spectrum has been challenging to explain. “We’ve had to undertake some cosmic archaeology to understand the ancient background story of the jellyfish,” said Hodgson. “Our working theory is that around 2 billion years ago, a handful of supermassive black holes from multiple galaxies spewed out powerful jets of plasma. This plasma faded, went quiet, and lay dormant. Then quite recently, two things happened—the plasma started mixing at the same time as very gentle shock waves passed through the system. This has briefly reignited the plasma, lighting up the jellyfish and its tentacles for us to see.”
The jellyfish is over a third of the Moon’s diameter when observed from Earth, but can only be seen with low-frequency radio telescopes. “Most radio telescopes can’t achieve observations this low due to their design or location,” said Hodgson. ...