X-shaped Cluster of Stars Spotted in the Centre of Our Galaxy

July 27, 2016 | Johannes Van Zijl

X-shaped cluster of stars in the Milky Way
Photo credit: NASA/JPL-Caltech; D.Lang/Dunlap Institute

X marks the spot!

Astronomers have spotted a large X-shaped structure consisting of clusters of stars in the center bulge of our Milky Way Galaxy.

Scientists analyzing computer-simulated models of the universe and earlier observations by astronomers of various galaxies including our own suggested the X-shape cluster of stars might exist, but no one had directly observed it before. Now Melissa Ness, lead author and Dustin Lang, co-author of the paper that described the latest findings, provide some of the best evidence yet.

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“There was controversy about whether the X-shaped structure existed,” says Dustin Lang in a media release,  “But our paper gives a good view of the core of our own galaxy. I think it has provided pretty good evidence for the existence of the X-shaped structure.”

Lang work through previously released data from the Wide-field infrared Survey Explorer (WISE). WISE was a space telescope launched by NASA in 2009 and was operating until 2011 taking infrared images of entire night sky.  Lang was initially doing research to help map galaxies beyond our Milky Way using data from WISE. To make it easier to explore some of the maps he made, he created a map-browsing website, where a collection of the WISE galaxy maps were hosted. Lang then posted a tweet on May 7th, 2015, which showed an image of the Milky Way Galaxy as captured by WISE.

“Ness saw the tweet and immediately recognized the importance of the X-shaped structure,” says Lang. “We arranged to meet at an upcoming conference we were both attending. The paper was born from that meeting. That’s the power of large surveys and open science!”

Our Milky Way is a spiral galaxy consisting of billions of stars. It has a mass of 700 billion times that of our suns and stretches 100,000 light-years in diameter. It consists of two spiral arms containing a large bulge of stars at its center. When viewed from within the plane of the galaxy, a peanut shape feature is visible through its center. The X-shape structure Lang and Ness have now discovered forms an important part of our galaxy’s bulge and it could reveal answers to how our galaxy formed.

“The bulge is a key signature of formation of the Milky Way Galaxy,” says Ness. “If we understand the bulge we will understand the key processes that have formed and shaped our galaxy.”

“The shape of the bulge tells us about how it has formed. We see the X-shape and boxy morphology so clearly in the WISE image and this demonstrates that internal formation processes have been the ones driving the bulge formation.”

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According to the media release by the Dunlap Institute for Astronomy & Astrophysics, astronomers think there are two potential ways the bulge could have formed: “it may have formed when the Milky Way Galaxy merged with other galaxies; or it may have formed without the help of external influences as an outgrowth of the bar, which itself forms from the evolving galactic disk. Lang and Ness’s finding supports the latter model which predicts the box- or peanut-shaped bulge and the galactic X.”

You can marvel at the image below with the X-shape clearly visible.

Close-up of the Milky Way's bulge with X-shape

An enhanced close up view of the Milky Way’s central bulge with an X-shape visible. Credit: D.Lang/Dunlap Institute

The findings were published in the July issue of the Astronomical Journal.

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