How Twitter led the way to finding the Milky Way's giant “X”

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Infrared image of the galactic center with the "X"-shaped star formation displayed prominently in the inset(Credit: NASA/JPL-Caltech)

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Prompted by a series of tweets, a pair of astronomers have used data from NASA's Wide-field Infrared Survey Explorer (WISE) orbital telescope to identify an image of a massive "X"-shaped star formation located in our galaxy's central bulge. The feature had been picked up in previous studies that observed the galactic center, but this is the first ever instance of an actual image of the unexplained phenomenon.

Our Milky Way is what is known as a spiral galaxy, and planet Earth is located in the Orion Spur of the Perseus spiral arm. While we know in general terms where we are, and what form our galaxy takes, we are constantly discovering clues that point to the evolutionary path taken by the Milky Way. Occasionally, we uncover a new large scale structural feature of our galaxy, which reveals itself as our methods of observing the heavens mature.

The latest large scale discovery regarding the structure of the Milky Way has its routes in an unlikely source ... a series of tweets. It all began in May 2015 when Dustin Lang, an astronomer from the University of Toronto, shared a series of images created from infrared data captured by the WISE telescope.

The infrared capabilities of WISE has allowed astronomers to peer through the interstellar clouds of dust and gas that characterise visible light images of our Milky Way, and observe bounty of cosmic objects that lurk behind the veil. Lang had posted the images to his Twitter feed following the culmination of a previous study he had undertaken attempting to map the disposition of nearby galaxies.

It didn't take long for astronomers to comb through the tweets and further infrared data from WISE that was made available via an interactive website, and to begin commenting on an apparent "X" shaped formation of stars in the central bulge.

The team used infrared data from WISE, and subtracted a model of predicted star distribution in a symmetrical bulge to reveal the formation(Credit: NASA/JPL-Caltech/D.Lang)

A central bulge is a feature shared by many spiral galaxies, which occurs when the central bar of a spinning galaxy buckles due to instabilities that creep in over time. This partial deformation leads to stars traversing an orbit that lays perpendicular to the disk of the galaxy. The Milky Way's central bulge appears somewhat like an American football when viewed from Earth, and it is within this feature that the "X" shaped star formation was discovered.

Postdoctoral researcher Melissa Ness, of the Max Planck Institute for Astronomy, Heidelberg, Germany, was among the astronomers who took note of the oddity. Ness contacted Lang, and soon after the two embarked on a collaboration aimed at analyzing the unusual "X"-like feature. Their work has effectively confirmed the presence of the "X" structure in the central bulge.

"To me, this study is an example of the interesting, serendipitous science that can come from large data sets that are publicly available," comments Lang. "I'm very pleased to see my WISE sky maps being used to answer questions that I didn't even know existed."

The discovery provides evidence for the argument that the Milky Way has experienced no large scale galactic mergers in the past 9 billion years, as any collision during this time frame would have significantly disturbed the "X" formation.

In more general terms, discoveries of features such as this allow astronomers to hone our understanding of the formation of our galaxy, and others like it, by developing new theories, or adapting existing ones to account for a new element, and discarding those that do not.

Astronomers are now engaged in further research aimed at discerning the composition of the many stars that make up the "X" feature.

Source: NASA

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