New Milky Way map reveals a wave of stars in our galaxy’s outer reaches

A new map reveals the outskirts of the Milky Way galaxy, including a wave of stars disturbed by a small galaxy on a collision course with our own.

Data collected from the European Space Agency’s Gaia mission and NASA’s Near Earth Object Wide Field Infrared Survey Explorer has been used by astronomers to map the galactic halo and this group of stars. Their findings appear in a study published Wednesday in the journal Nature.

Our Milky Way is a galaxy with multiple spiral arms emanating from a central disk. The empty-looking halo lies outside of these swirling arms. But there may be more to the halo than meets the eye.

https://www.spitzer.caltech.edu/images/1923-ssc2008-10a-A-Roadmap-to-the-Milky-Way Like early explorers mapping the continents of our globe, astronomers are busy charting the spiral structure of our galaxy, the Milky Way. Using infrared images from NASA's Spitzer Space Telescope, scientists have discovered that the Milky Way's elegant spiral structure is dominated by just two arms wrapping off the ends of a central bar of stars. Previously, our galaxy was thought to possess four major arms. This artist's concept illustrates the new view of the Milky Way, along with other findings presented at the 212th American Astronomical Society meeting in St. Louis, Mo. The galaxy's two major arms (Scutum-Centaurus and Perseus) can be seen attached to the ends of a thick central bar, while the two now-demoted minor arms (Norma and Sagittarius) are less distinct and located between the major arms. The major arms consist of the highest densities of both young and old stars; the minor arms are primarily filled with gas and pockets of star-forming activity. The artist's concept also includes a new spiral arm, called the "Far-3 kiloparsec arm," discovered via a radio-telescope survey of gas in the Milky Way. This arm is shorter than the two major arms and lies along the bar of the galaxy. Our sun lies near a small, partial arm called the Orion Arm, or Orion Spur, located between the Sagittarius and Perseus arms.

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The halo, which hosts a small population of stars, is also thought to contain a lot of dark matter. This mysterious substance, which is invisible and has eluded scientists for decades, is thought to comprise most of the mass in the universe.

A small neighboring galaxy, known as the Large Magellanic Cloud, orbits the Milky Way. The data used to create the map revealed that, like a ship, the Large Magellanic Cloud has cut through the Milky Way’s outer halo. This disturbance has left a rippling wave of stars behind the Large Magellanic Cloud, which is in the halo.

A collision of galaxies

Currently, the Large Magellanic Cloud is 160,000 light-years from Earth, and it only has about a quarter of the mass of our giant galaxy.

This vibrant image from NASA's Spitzer Space Telescope shows the Large Magellanic Cloud, a satellite galaxy to our own Milky Way galaxy.

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Research from 2019 suggests it will catastrophically collide with our own galaxy in 2 billion years.

The impact has a chance of sending our solar system hurtling through space.

The wake created by the Large Magellanic Cloud is about 200,000 light-years to 325,000 light-years from the galactic center.

While previous research suggested its existence, this new data provides confirmation, as well as the most detailed and accurate map of the galaxy’s outskirts.

Astronomers have released a new map highlighting the outermost region of the Milky Way.

In the image, the strip in the middle represents a 360-degree view of our galaxy overlaying a map of the galactic halo. A bright wave in the bottom left of the image is the wake of stars, and to the right is the Large Magellanic Cloud and the path it is taking.

A large, light blue feature in the top right shows a high concentration of stars in our galaxy’s northern hemisphere.

Understanding dark matter

The ripple left by the dwarf galaxy’s movement is also an opportunity to study dark matter. Even though dark matter is invisible, it provides structure throughout the universe – including the foundation for galaxies.

So if the Large Magellanic Cloud can cut through the Milky Way’s halo and leave a wave of stars, the same ripple should essentially act as an outline of the dark matter.

Dark matter is essentially pulling on the Large Magellanic Cloud to slow it down, shrinking the dwarf galaxy’s orbit around the Milky Way and causing the eventual collision.

While it sounds violent, galactic collisions are what have created the massive galaxies populating our universe – and our own galaxy has previously experienced mergers before.

“This robbing of a smaller galaxy’s energy is not only why the (Large Magellanic Cloud) is merging with the Milky Way, but also why all galaxy mergers happen,” said Rohan Naidu, study co-author and a doctoral student in astronomy at Harvard University, in a statement. “The wake in our map is a really neat confirmation that our basic picture for how galaxies merge is on point!”