The Milky Way has a shattered arm which may reveal its galactic history.

Scientists have discovered a strange "break up" in the spiral arms of our Milky Way galaxy which could tell us more about its galactic history.

The grouping of young stars and gas regions is outlined by NASA's Jet Propulsion Laboratory (JPL) resembling "a splinter coming out of a board of wood" from the plane of the arms of the spiral Milky Way.

Finding this characteristic was an achievement in itself, as the Earth is in the Milky Way. In a press release, JPL officials stated that the difficulty of doing such a search is a bit like standing in Times Square while trying to draw a map of the island of Manhattan.

The researchers followed the trail using infrared eyes or looking for heat from NASA's Spitzer Space Telescope (before the observatory was shut down in January 2020) and the Gaia mission of the European Space Agency, which measures distances and stellar displacements. Gaia's last major data dissemination took place in July.

The new study focused on a nearby region of one of the Milky Way's arms called the Sagittarius Arm — home of the famous "Pillars of Creation" stacks of stars that form part of the Eagle Nebula (Messier 16.) Between Spitzer and Gaia, the combined data show that Sagittarius is full of young stars that travel through space, at about the same speed, and in the same direction.

“A key property of the spiral arms is how tightly they wind around a galaxy,” Michael Kuhn, an astrophysicist at the California Institute of Technology and lead author of the new paper, said in the JPL statement.

Kuhn added that earlier models of the Milky Way suggested the winding, measured by the "pitch angle" compared to a perfect circle of 0 degrees, previously suggested Sagittarius had a pitch angle of roughly 12 degrees. New observations indicate that the Sagittarius has a pitch angle of close to 60º. Why isn't that clear, though?

Astronomers are still trying to figure out how and why the arms of galaxies form, and JPL said the new study could yield some clues. Because the newly discovered stars were formed around the same time zone and zone, they were likely influenced by larger changes occurring in the Milky Way. These changes involve the severity and shear associated with the rotation of the galaxy.

"This structure is a small piece of the Milky Way, but it could tell us something significant about the galaxy as a whole," said co-author Robert Benjamin, an astrophysicist at the University of Wisconsin-Whitewater, in the same statement.

Benjamin is also the lead researcher in the Galactic Legacy Infrared Mid-Plane Extraordinary Survey (GLIMPSE), which the new study also used. GLIMPSE comprises about 100,000 new stars discovered by Spitzer over the course of his life.

A peer-reviewed research paper was published in the July 2021 edition of Astronomy and Astrophysics.