Galaxy’s “smoking gun” is spectacular plume of gas

By Gemma Chilton 25 February 2016
Reading Time: 2 Minutes Print this page
A nearby galaxy is moving so fast it has left a 300,000-light-year plume of star-making gas in its wake.

THERE’S A GALAXY about 55 million light years away that scientists discovered some time ago contains much less gas than expected. However, until now, they had no idea where all that gas had gone.

“We didn’t have the smoking gun, the clear evidence of direct removal of gas from the galaxy,” said Dr Luca Cortese, an astrophysicist at the International Centre for Radio Astronomy Research in Western Australia – part of an international team of scientists that recently found the galaxy’s missing gas.

The galaxy is called NGC 4569 and it sits in the Virgo cluster, a group of galaxies 55 million light years away from our own Milky Way. 

As it turns out, the galaxy is moving through the cluster so fast – at about 1200km per second – that gas is being stripped from it, leaving a spectacular plume in its wake. That tail of hydrogen gas (the material new stars are made of) is about 300,000 light years across – about five times bigger than the galaxy itself, and about three times bigger than our Milky Way. 

“Like wind on your face”

“What’s very nice is that if you measure the mass of the stream, it’s the same amount of gas that is missing from the galaxy’s disc,” said Luca.

Luca explained that big clusters of galaxies trap a lot of hot gas, “so when a galaxy enters the cluster it feels the pressure of all the gas, like when you feel the wind on your face, and that pressure is able to strip matter away from the galaxy,” he said.

Commenting on the research, Dr Alan Duffy, an astronomer from Swinburne University in Melbourne, who wasn’t involved in this study, said “this is a beautiful piece of work resolving a mystery of missing gas in a distant galaxy.”

“If you’ve ever felt the wind push back against your hand when driving, you can imagine how much this ‘ram pressure’ can push back when you’re travelling thousands of times faster,” he said. “This has pushed the gas right out of the galaxy, starving it of the basic ingredients to form any new stars, with the remains forming a comet-like tail stretching behind it.”

The discovery was made when the research team used a super-sensitive camera on the Canada France Hawaii Telescope to observe NGC 4569 for longer than ever before.

The findings are published in the journal Astronomy & Astrophysics.

Luca said this could be the first of many galaxies found to have long tails of gas extending from them. “It’s pretty exciting because this was just a pilot and we only targeted the brightest spiral galaxy in the Virgo cluster,” he said.