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Does my star look big in this? Milky Way 50 per cent fatter than expected

Slap that and ride the ripples

Vid The Milky Way galaxy could be up to 50 per cent wider than the previously estimated – a whopping 150,000 light years across, potentially – according to boffins.

"In essence, what we found is that the disk of the Milky Way isn't just a disk of stars in a flat plane: it's corrugated," said Heidi Newberg, professor of physics, applied physics, and astronomy in the Rensselaer School of Science in New York.

"As it radiates outward, we see at least four ripples in the disk of the Milky Way. While we can only look at part of the galaxy with this data, we assume that this pattern is going to be found throughout the disk."

Prof Newberg's team has been going through the data from the Sloan Digital Sky Survey (SDSS) which was carried out by the Apache Point Observatory in New Mexico.

The observatory spent eight years studying a significant section of our home galaxy after Prof Newberg spotted a dense clump of stars on the outer edge of the galaxy in 2002. That thicket of suns was raised up over the galactic plane, which she dubbed the Monoceros Ring.

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The ring is a long strand of matter that encircles the Milky Way three times, and is about 200,000 light years long. It contains 100 million solar masses of material, or 1.9 x 1038 kilograms.

It was thought the ring was the smeared remains of a dwarf galaxy that had been pulled apart by our more massive Milky Way. But the data suggests that the matter is from our own galaxy, and exists in ripples around the galactic core because it has been teased out by an impact with another galaxy.

"It's very similar to what would happen if you throw a pebble into still water; the waves will radiate out from the point of impact," said Prof Newberg.

"If a dwarf galaxy goes through the disk, it would gravitationally pull the disk up as it comes in, and pull the disk down as it goes through, and this will set up a wave pattern that propagates outward. If you view this in the context of other research that's emerged in the past two to three years, you start to see a picture is forming."

Yan Xu, of the National Astronomical Observatories of China who is a visiting scientist at Rensselaer, coauthored a paper on the research with Prof Newberg – a paper published in the latest issue of the Astrophysical Journal. The pair postulate that the new information shows the galaxy is at least 150,000 light years across.

"Going into the research, astronomers had observed that the number of Milky Way stars diminishes rapidly about 50,000 light-years from the center of the galaxy, and then a ring of stars appears at about 60,000 light-years from the center," said Xu.

"What we see now is that this apparent ring is actually a ripple in the disk. And it may well be that there are more ripples further out which we have not yet seen." ®

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