Cosmic Finger Taps Our Galaxy's Shoulder
The leading arm of gas streaming from the Magellanic Clouds is piercing the disk of the Milky Way.
Credit: John Rowe Animations

As if reaching out with a come-hither motion, a giant gas finger emanating from two neighboring galaxies has hooked into the starry disk of the Milky Way.

This extremity of hydrogen gas is actually the pointy end of the so-called Leading Arm of gas that streams ahead of two irregular galaxies called the Large and Small Magellanic Clouds.

The fate of these nearby galaxies, which are impacted by the Milky Way's gravity, has been somewhat of a mystery. The new finger findings suggest that the Magellanic Clouds will eventually merge with the Milky Way rather than zooming past.

Located about 160,000 light-years from Earth, the Large Magellanic Cloud (LMC) is only one-twentieth the diameter of our galaxy and contains one-tenth as many stars. The Small Magellanic Cloud resides 200,000 light-years from Earth and is about 100 times smaller than the Milky Way.

?We?re thrilled because we can determine exactly where this gas is plowing into the Milky Way,? said research team leader Naomi McClure-Griffiths of CSIRO?s Australia Telescope National Facility.

Called HVC306-2+230, the gas finger is gouging into our galaxy's starry disk about 70,000 light-years away from Earth. In the night sky, the contact point would be nearest the Southern Cross.

Until last year, astronomers thought the Magellanic Clouds had orbited our galaxy many times. This scenario held a gloomy outlook for the clouds, which were said to be doomed to be ripped apart and swallowed by the gravitational goliath.

But then new Hubble Space Telescope measurements revealed the clouds are paying our galaxy a one-time visit rather than being its lunch.

McClure-Griffiths' results, however, are more in line with the previous tale pegging the Milky Way and the Magellanic Clouds as long-time companions. McClure-Griffiths remarks that this isn't the final word and that both theories are still on the table.

By pointing out the spot of contact between the Leading Arm and our galactic disk, the recent study will help astronomers to predict where the clouds themselves will travel in the future.

?We think the Leading Arm is a tidal feature, gas pulled out of the Magellanic Clouds by the Milky Way?s gravity,? McClure-Griffiths said. ?Where this gas goes, we?d expect the clouds to follow, at least approximately.?

In the distant future, the three galaxies could become one.

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