May 6, 2004. Australian astronomers have discovered a huge arm of the Milky Way which means maps of our galaxy will have to be redrawn.
The new gassy limb is 77,000 light years long and several thousand thick.
The mass of hydrogen runs along the galaxy's outermost edge around the four main arms that swirl around the core.
As it is not in the visible part of the light spectrum, it cannot be seen by telescope and was discovered by staff at the Australia National Telescope Facility in New South Wales who were mapping the distribution of hydrogen.
Most of the Milky Way is obscured by interstellar dust, but hydrogen emits radio waves which pass through the dust clouds and which thus make it detectable by radio telescope.
Lead astronomer Naomi McClure-Griffiths told the New Scientist journal: "We see it [the arm] over a huge area of sky."
Astronomers are amazed that the feature had been overlooked, said New Scientist.
"It was quite clearly seen in some of the previous surveys
but it was never pointed out or given a name," said US astrophysicist