Photo by: NASA


The Milky Way Broke its Arm (But is Totally Okay)

The Milky Way is a giant, magnificent, truly transcendently beautiful spiral arm galaxy. It’s too bad we can’t get a decent picture of it. The problem is that we live inside it, and so astronomers have to work extra-hard to construct an accurate map.

October 14, 2021

Look, you try making a sketch of your house while staying inside it.

By making such a sketch of our galactic neighborhood using a map of newborn stars, a team of astronomers have found that one of our nearby arms broke itself in the recent past. But it’s okay, because spiral arms do this all the time.

To make the map of nearby spiral arms astronomers had to look for nebulae and clumps of newborn stars. They look for nebulae because spiral arms are major sites of star formation, and stars are born in nebulae. They look for newborn stars because after stars are formed, they have a tendency to leave home and just wander around.

To look for newborn stars, the astronomers went through old, archived data from the Spitzer space telescope. Spitzer is an infrared telescope, and infrared light is really, really good as passing through clouds of gas (just like infrared light is really good at passing through walls and giving you night vision). Using the Spitzer, the astronomers could spot all the newly forming stars, still cocooned in their parent nebulae.

Photo by: NASA


But identifying the young stars and the nebulae is only part one. Part two is figuring out how far away they are, which is one of the most difficult jobs in all of astronomy. Thankfully, the astronomers had at their disposal the results of the Gaia satellite, which produced a survey of over a billion nearby stars, giving anyone and everyone a complete census of our neighborhood.

That’s how they found the break – a map of nearby young stars revealed a structure that simply didn’t align with anything else.. It’s a splinter of a nearby major spiral arm, the Sagittarius Arm. When it comes to broken arms, it’s definitely a compound fracture: the splinter of stars is sitting about 50 degrees off of the main line of the Sagittarius. It begins about 4,000 lightyears away from us and extends for another 2,500 lightyears. That’s far smaller than the Sagittarius arm itself, but still truly massive.

The break (also known as a spur or a feather, if you want) features some popular stargazing targets: the Eagle Nebulae (home of the “Pillars of Creation” that adorns desktops background across the globe), the Omega Nebulae, the Trifid Nebula, and the Lagoon Nebula.

Astronomers have known that major spiral arms in a galaxy often splinter and break, and this new discovery gives us the best possible opportunity to see how these dynamics play out. Over time, the stars in this region will slowly disperse into the galactic background, dissolving the break…and healing the arm.

Dive Deeper into the Cosmos

Paul M. Sutter

Paul M. Sutter is an astrophysicist at Stony Brook University and the Flatiron Institute, host of Ask a Spaceman and Space Radio, and author of How to Die in Space.

Next Up

Anatomy Lesson: The Milky Way

The Milky Way is a giant, sprawling, beautiful spiral galaxy. It's also your home. Let's take a little tour.

See the First Image of the Milky Way’s Huge Black Hole

For the first time, a colorized image of the supermassive black hole located at the center of our own Milky Way Galaxy was shared by astronomers.

Romeo and Juliet: The Story of Galaxy Collisions

Our Milky Way galaxy is on a collision course. With destiny. With destruction. With fate. With our nearest neighbor, Andromeda. You can stream HOW THE UNIVERSE WORKS on discovery+.

Going for Gold: The Biggest Explosion in the Universe

Meet the humble Ophiuchus galaxy cluster. It’s just another dense clump of galaxies, one of approximately a bajillion, dotting the universe. It sits about 240 million lightyears away from Earth.And its heart is missing.

The Cost of Global Satellite Internet: Worse Astronomy

A few billionare-backed companies have ambitious goals: launching tens of thousands of communication satellites to provide global high-speed internet access. Elon Musk’s StarLink, Jeff Bezos’ Project Kuiper, One Web, GuoWang, and more are all competing for this lucrative market. In less than a decade, we can expect over 50,000 new satellites to encircle the Earth. That’s about ten times more than are currently active.

When Did the First Stars Shine?

Our universe is home to up to two trillion galaxies, with each galaxy hosting hundreds of billions of stars. That’s…a lot of stars. Each one a ball of fearsome energies, powered by the nuclear fusion of fundamental elements in their hearts. Each one pouring out light into the empty cosmos, illuminating our universe for our wonder and delight.

The Nobel Prize Fell Into a Black Hole (and That’s a Good Thing)

The 2020 Nobel Prize in Physics is being awarded to scientists to have dedicated their careers to the study of black holes.

All Hail Ganymede, King of the Moons

NASA’s Juno probe, the supremely awesome Jupiter orbiter, recently captured some stunning images of Ganymede, the largest moon of Jupiter, during the orbiter’s 34th trip around the giant.

The Head of NASA Believes in Aliens

“Are we alone? Personally, I don’t think we are,” Bill Nelson, former astronaut and Chief of NASA, said in a video interview.

Watch the Super Flower Blood Moon Total Lunar Eclipse

Those located in the Americas, Europe, or Africa can see this rare total lunar eclipse during the night of May 15, 2022.

Related To: