It seems like a cliche, but "X" actually does mark the spot in the center of our galaxy. Researchers working with data from the Wide-field Infrared Survey Explorer (WISE) mission have confirmed the existence of a strange X-shaped structure at the heart of the Milky Way, reports NASA.
The enormous X is made from a bulge of stars that are moving around the galactic center, perpendicular to the plane of the galaxy, and in and out radially. Such bulges are common within disk galaxies like the Milky Way, where "stellar bars" may form. These are essentially stars moving in a box-shaped orbit around the center. The way the planes of these orbits form from our view happens to take the shape of an X.
It's a profound discovery, one which helps to enlighten scientists about how the galaxy has formed.
"We see the boxy shape, and the X within it, clearly in the WISE image, which demonstrates that internal formation processes have driven the bulge formation," said Melissa Ness, lead author on the research. "This also reinforces the idea that our galaxy has led a fairly quiet life, without major merging events since the bulge was formed, as this shape would have been disrupted if we had any major interactions with other galaxies."
In other words, the X shape is a sign of cosmic purity, in the sense that such perfect shapes like this wouldn't have formed if the galaxy had collided or merged with another galaxy. If the Milky Way had crossed paths with another galaxy, the idyllic X shape would have been destroyed.
This is lucky, and not just for aesthetic reasons. By studying this inner galactic bulge in such unadulterated form, researchers can more easily piece together the story of how our galaxy took shape.
"The bulge is a key signature of formation of the Milky Way," explained Ness. "If we understand the bulge we will understand the key processes that have formed and shaped our galaxy."