You live in the right galaxy: Milky Way to eat Small Magellanic Cloud even sooner

You've only got a few billion years, little buddy


Astronomers have long known the nearby galaxy, the Small Magellanic Cloud, was being monstered by the Milky Way and the Large Magellanic Cloud. But new imaging captured by the Australian Square Kilometre Array Pathfinder (ASKAP) has made it clear that the little star-factory has only a handful of billion years left.

As the Small Magellanic Cloud's (SMC's) stars blow up, the ASKAP observations found, they accelerate gas fast enough that it departs their home galaxy entirely, to be captured by the Large Magellanic Cloud (LMC) and the Milky Way.

ASKAP is the precursor to Australia's part of the full square kilometre array and made its first observations in early 2017.

The Pathfinder was recently used to capture a deep and detailed image of the Small Magellanic Cloud, and returned an image capturing five degrees across the sky.

Co-lead researcher Professor Naomi McClure-Griffiths of the Australian National University told The Register astronomers knew the SMC has “an immense gaseous stream that tails behind the Small Magellanic Cloud and wraps all around the Milky Way”.

With the ASKAP observations in hand, McClure-Griffiths's team shed light on the process that's dragging the gas away from the SMC.

“The SMC has a lot of star formation, so as they reach the end of their life they explode and push gas away,” she said.

The problem for the SMC is gravity – there isn't enough of it. “It's very hard to hold on to that gas if it gets a kick from a supernova – the gas disappears out of the galaxy.”

That's where the Milky Way and the Large Magellanic Cloud come in: the two larger galaxies have greater gravity, so they're consuming the ejected gas and using it for their own star-formation.

That hypothesis, McClure-Griffiths said, was made possible by ASKAP's extra sensitivity, as it let the researchers see more gas. And not just see it, but behold the kind of detail McClure-Griffiths said is “like you just got your new reading glasses”.

The Australian National University's announcement also noted that while instruments like Spitzer (NASA) and Herschel (ESA) have gathered many SMC images, they're more focussed on dust and stars within the galaxy.

“The new radio image finally reaches the same level of detail as those infrared images, but on a very different component of the galaxy's make-up: its hydrogen gas.

“Hydrogen is the fundamental building block of all galaxies and shows off the more extended structure of a galaxy than its stars and dust.”

♬ Tonight is the night... when eight become one ♬

McClure-Griffiths also explained that ASKAP has made this kind of observation far easier to conduct. Australia's current premier telescopes, the Australia Telescope Compact Array (ACTA) at the NSW country town of Narrabri, needed 300 individual images to capture a similar survey of the SMC.

Dave McConnell of Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO), who leads the effort to commission ASKAP and oversee its early science, explained that five degrees is a “substantial piece of sky for a radio telescope to be able to image in one go.

“To make an image like this, something that's a large part of the sky, is possible but very laborious,” he said.

Referring to the 20-year-old ACTA imaging run McClure-Griffiths named, McConnell said “it took 320 separate pointings over eight nights to gather all that data.”

The SMC image captured by ASKAP used 16 of the telescope's 36 beams, and each of those in-use beams comprised 36 hexagonal patches of sky.

McConnell added that there's still “a lot of cleverness” needed to combine the dozen hours of observations into a single image, but that ASKAP is “so much better mapped to this kind of software and data reduction. Getting everything to work properly for eight nights with no gaps … is a much bigger problem.” ®

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