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Astronomers detect Milky Way’s border

Australian scientists say the thick arm of interstellar gas wraps around the outskirts of our home galaxy.
/ Source: Reuters

Astronomers have discovered an extra cosmic arm in the Milky Way that they believe wraps around the outskirts of the vast galaxy like a thick gas border.

Astronomers at the Commonwealth Scientific and Industrial Research Organization, or CSIRO, hope the find will help paint a better picture of the Milky Way galaxy, which is home to Earth.

CSIRO scientist Naomi McClure-Griffiths said the gas border, which is 6,500 light-years thick, showed that the Milky Way had a structure similar to those of most other galaxies, which have gassy spiral arms extending beyond the more central stellar spiral arms.

Astronomers believe the Milky Way has about four arms made up of hydrogen gas, dust and stars spiraling out from its center. McClure-Griffiths said the newly discovered gas border is about 60,000 light-years from the centre of the Milky Way.

A light year is the distance that light travels in a year, which is about 6 trillion miles (10 trillion kilometers).

"We have known there was gas out there, but we haven't known that there was a structure out there. We thought there was just a smooth drop-off, that the galaxy just sort of slid away," McClure-Griffiths told Reuters. "It is at the furthest reaches of the galaxy and is the last thing you see before the galaxy disappears."

McClure-Griffiths and a small team of scientists were investigating the hydrogen gas in the disk of the Milky Way when they stumbled across the extra arm, which they believe could connect up with one of the galaxy's central stellar arms.

The finding has been submitted for publication to the Astrophysical Journal of the American Astronomical Society, she added.