Space Jellyfish Spotted

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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.

“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.”

Credit: ICRAR

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.

The MWA—a precursor to the Square Kilometre Array (SKA)—is located at CSIRO’s Murchison Radio-astronomy Observatory in remote Western Australia.

The site has been chosen to host the low-frequency antennas for the SKA, with construction scheduled to begin in less than a year.

Tile 107, or “the Outlier” as it is known, is one of 256 tiles of the MWA located 1.5km from the core of the telescope. The MWA is a precursor instrument to the SKA.

 Photographed by Pete Wheeler, ICRAR.

Professor Johnston-Hollitt, Mr Hodgson’s supervisor and co-author, said the SKA will give us an unparalleled view of the low-frequency Universe.

“The SKA will be thousands of times more sensitive and have much better resolution than the MWA, so there may be many other mysterious radio jellyfish waiting to be discovered once it’s operational.
 

Composite image of the SKA-Low telescope in Western Australia. The image blends a real photo (on the left) of the SKA-Low prototype station AAVS2.0 which is already on site, with an artists impression of the future SKA-Low stations as they will look when constructed. These dipole antennas, which will number in their hundreds of thousands, will survey the radio sky in frequencies as low at 50Mhz.

 Credit ICRAR and SKAO.
 

 
Contacts and sources:
Pete Wheeler. The International Centre for Radio Astronomy Research (ICRAR)
Vanessa Beasley,  Curtin University
Professor Melanie Johnston-Hollitt (ICRAR / Curtin University)