When astronomer Dustin Lang tweeted out some galaxy maps he made using publicly available data from NASA’s Wide-field Infrared Survey Explorer (WISE) in 2015, he wasn’t expecting for them to lead to a new way of looking at our galaxy, the Milky Way.
He’d been working with the WISE data as part of his work on the Sloan Digital Sky Survey, which performs detailed observations of selected galaxies to map the large-scale structure of the universe.
“I released the results in the hope that they would be useful for other scientific studies,” said Lang, a research associate for the Dunlap Institute for Astronomy & Astrophysics at the University of Toronto, who also built an interactive site to help people explore the maps.
He also admits that part of it was “just showing off.
“Scientists on Twitter often share sneak peeks of interesting results or pretty pictures,” said Lang, whose work combines computer science and astronomy.
Melissa Ness, a researcher at the Max Planck Institute for Astronomy in Germany, saw the “zoomed-out, whole-sky view” on Twitter and recognized an X-shaped bulge, or tightly packed group of stars found in spiral galaxies, in the center of the Milky Way.
“It was simply the most fantastic image of the Milky Way bulge that I had seen,” Ness said. “I studied the bulge for my Ph.D. and so was well aware that there are numerous works and data that demonstrate that there is an underlying X-shape in the bulge, and in fact it had been modeled in detail from these prior works, but with that image that Dustin had made, we were clearly seeing this X-shape directly in a real image of the inner region of the galaxy, for the first time.”
Ness emailed Lang immediately to let him know the significance of this shape within his map. They realized they would be at the same conference in Michigan in a couple of weeks and once they met, decided to collaborate on and author a study analyzing the X.
Using email correspondence to combine their different skill sets, Lang supplied the images using WISE data and Ness provided scientific interpretation, Lang said.
WISE took two infrared surveys of the entire sky in 2010, which allowed for better visibility of galaxies and their structures because the infrared light overcomes the usual visible light issue of dust.
The Milky Way is a rotating barred spiral galaxy full of stars, gas and dust that is 100,000 light-years wide. The bulge is at the center, surrounded by a flat, pancake-shaped disk with spiral arm extensions. It also has a “bar” of stars moving in a box-shaped orbit around the center, according to NASA. If that bar buckles, then the stars would be moving in a perpendicular motion, creating an X-shape of stars orbiting in what looks like either a peanut or box depending on how it forms.
Previous studies already suggested the X-shape of the bulge because they could see a dip in the number of stars in the center of the galaxy comprising the intersection of the two arms of the X, Ness said. Other images from NASA’s Cosmic Background Explorer satellite (COBE) had indicated a box structure for the bulge. Both of these pointed to the collapsed bar, but there was controversy over how it might have formed — as a natural outgrowth of the massive bar that formed from the disk, or from merging with other galaxies.
But the Milky Way hasn’t merged with another large galaxy in billions of years. That would have disrupted the shape, Ness said.
Using the infrared data, Ness and Lang were able to actually see the clearest view of the X-shape yet. What they discovered is that within the bar, the big X-shaped structure is full of crossing stars. It looked like a 3-D football in comparison to the flat disk of the Milky Way.
“This shape implies that the bulge has therefore formed in large part via dynamical instabilities from the disk,” Ness said. “This basically tells us about how the galaxy has formed.”
Ness is continuing to work on studying the Milky Way and the chemical composition and movement of the stars within the bulge to increase our understanding of the galaxy we live in.
This study, and the details of how it came to be, can also inspire future researchers to use social media as a way to connect with their colleagues as well as encourage more publicly available data from surveys, Lang said.
Ness is a proponent of open science because she believes “we are a community all building on each others efforts and that is made possible via distribution of the data products, results and sharing of the scientific exploration.”
“I really like the fact that this study happened at all — to me, it’s an example of the interesting, serendipitous science that can happen when people publicly release their data and try to communicate their results to the public and other scientists,” Lang said. “I don’t normally study Milky Way structure, so it was fun to learn how the WISE data could be used to answer a question I didn’t even know existed! This study wouldn’t have happened if the WISE team had not gone to great effort to create a very high-quality public data release.”