Within certain astronomical circles, it was immediately clear Dustin Lang’s tweet was provocative. Not controversially so – lacking celebrity skin or celebrity abuse, his message would leave the Internet unbroken.

There was, however, a curious bulge.

Lang’s photo succeeded in cracking open a scientific mystery of a hypothesized – though until now unconfirmed – X-shaped lump at the center of the Milky Way galaxy.

“The bulge is a key signature of formation of the Milky Way Galaxy,” Melissa Ness, a postdoctoral researcher at the Max Planck Institute for Astronomy in Heidelberg, Germany, said in a statement. “If we understand the bulge we will understand the key processes that have formed and shaped our galaxy.”

Not that Lang set out to play paparazzo to the Milky Way’s hidden features. Lang, an astronomer at the University of Toronto’s Dunlap Institute, had been mapping out galaxies thanks to data from WISE, NASA’s Wide-field Infrared Survey Explorer. NASA launched the spacecraft in 2009, and by 2011, WISE had scanned the sky with infrared light twice over. All told, within WISE’s data sit some 750 million stars, asteroids, galaxies and other heavenly objects.

To canvass the intergalactic neighborhood, Lang combs through that information, translating it into pictures. Occasionally, he tosses interesting images up on social media.

WISE was designed to look outward, not inward. But the picture Lang tweeted in May 2015 concerned something a little closer to home – the Milky Way, that spiral disk of stars and dust that also contains you, your loved ones and everything else in the solar system.

Next to galactic whoppers like M87 and Hercules A, the Milky Way is a bit of a runt. By any other standard, though, it is incomprehensibly large, 100,000 light-years across and boasting about 400 billion stars.

It is possible to see an arm of the Milky Way with the naked eye, if the sky is clear of clouds and light pollution – a fluffy glowing band that arcs through the night. What is impossible to spot without some technological help is the massive bulge at the galactic center, obscured by interstellar dust and extreme distance. Using powerful telescopes that sense nonvisible light, such as X-rays, astronomers can pierce the veil of space. At the very heart, like the eye of a hurricane, scientists believe exists a supermassive black hole, named Sagittarius A*.

In 2010, NASA's Wide-field Infrared Survey Explorer (WISE) mission observed the entire sky twice. Astronomers used these data to point out the X-shaped structure in the bulge of the Milky Way, contained in the small circle at center, as well as the inset image. The circled central portion covers roughly the area of sky that would be blocked by a basketball when held out at arm’s length. NASA/JPL-Caltech/D.Lang

In 2010, NASA’s Wide-field Infrared Survey Explorer (WISE) mission observed the entire sky twice. Astronomers used these data to point out the X-shaped structure in the bulge of the Milky Way, contained in the small circle at center, as well as the inset image. The circled central portion covers roughly the area of sky that would be blocked by a basketball when held out at arm’s length. NASA/JPL-Caltech/D.Lang

It also turns out the Milky Way’s gut buckles outward in an unusual pattern. The bulge, made of a cluster of ancient stars, was visible in the center of Lang’s tweet. The shape caught the eye of several astronomically inclined Twitter users, but it was Ness who recognized its true significance.

Of this bulge, “there were hints of it in previous imaging, and some good indirect evidence,” Lang said, in an email he wrote to The Washington Post, from a telescopic observatory in Chile. “The beautiful images we get from WISE provide a much higher-resolution view, making the X more clear.” Computer models implied that the X-shape should exist, and other spiral galaxies like the Milky Way have similar bulges, too.

Ness and Lang recently published the discovery in the Astronomical Journal, noting that, in the parlance of astronomers, the thick middle of the Milky Way has a “boxy/peanut morphology.” In other words, if you squashed it into a flat image, the structure would look a bit like the letter X.

There had been some debate about whether this feature existed. In their paper, the scientists say the debate should be put to rest, saying for the first time that the X-shape was “irrefutably” documented. The bulge itself is made of a strip of orbiting stars. And as the galaxy grew, scientists believe the bar scrunched inward, giving the galaxy its X.

“So, yes, this really should put the argument about this to rest at this point,” Ness wrote to The Post in an email early Thursday. “It’s also the clearest view we have of the bulge and inner galaxy.”

To reveal the X shape in the Milky Way’s central bulge, researchers took WISE observations and subtracted a model of how stars would be distributed in a symmetrical bulge. NASA/JPL-Caltech/D.Lang

To reveal the X shape in the Milky Way’s central bulge, researchers took WISE observations and subtracted a model of how stars would be distributed in a symmetrical bulge.
NASA/JPL-Caltech/D.Lang

The astronomers say that examining the stars in the bulge – determining their age and elemental contents – could shine light on our early galactic history. And that the structure exists provides evidence that the Milky Way had not suffered any intergalactic trauma.

The X-shape, as Lang said he understands it, “would be disrupted if, for example, the Milky Way had collided with another galaxy in the past few billion years. Its existence tells us about our galaxy’s quiet life. In a collision, the stars in the X would probably have been thrown off those orbits into rounder, more mixed-up orbits.”

It is not completely unprecedented for social media to beget scientific discovery – in 2015, biologists caught wind of a strange new carnivorous plant species after a photo of it circulated through Facebook. For many researchers, Twitter is like peeking into another scientist’s notebook, said Lang, who is currently mapping the night sky in visible and near-infrared light. It is a place to post “work-in-progress and the frustrations and triumphs of their day-to-day work.”

He added: “I really enjoyed this study, because it’s an example where going to the effort of publicly releasing data and preparing ‘pretty picture’ images led to my WISE maps being used to answer a question totally different from what I was using them for.”