Science 4 min read

Collision with Dwarf Galaxy was Responsible for Milky Way's Ripples

Alex Mit /

Alex Mit /

Our home galaxy the Milky Way is so massive and large that it takes a photon of light around 100,000 years — or maybe even 50 percent more — to cross its stellar disk. It belongs to a type of spiral galaxies, shaped like a flat disc with a bulging center and spiraling arms of stars, gas, and dust.

But our galaxy isn’t floating around the universe alone. It has some cosmic neighbors in the Local Group, like the two dwarf galaxies known as the Small and Large Magellanic Clouds.

Last year, scientists reported the discovery of an odd dwarf galaxy on the far outskirts of the Milky Way, about 130,000 light-years away from Earth. They named it Antlia 2.

About the size of the Large Magellanic Cloud, Antlia 2 is however 10,000 times less brighter. This faintness doesn’t fit into models of galaxy formation and this got the attention of astrophysicists who wanted to know more about this oddball galaxy.

New data lead scientists to believe that the Milky Way is still reeling from a collision with Antlia 2 hundreds of million years ago.

Dark Dwarf Galaxy Crashed Into the Milky Way

The discovery of Antlia was made possible thanks to data from the ESA’s Gaia mission, a space telescope launched in 2013 to conduct a full-sky survey, mapping over 1 billion stars in and around our galaxy.

In 2009, Sukanya Chakrabarti, an astrophysicist from the School of Physics and Astronomy at Rochester Institute of Technology (RIT) has predicted the location of a dark-matter dominated dwarf galaxy through a dynamical analysis. This location closely matches the current location of Antlia 2.

Now, Chakrabarti has used data from the Gaia mission to calculate the past trajectory of Antlia 2 and found that this dwarf galaxy would have swept through the Milky Way and caused the ripples still visible in its outer gas disc.

Simulation of how the Milky Way and the dwarf galaxy Antilia 2 collided 3 billion years ago | Image courtesy of Sukanya Chakrabarti/Rochester Institute of Technology
Simulation of how the Milky Way and the dwarf galaxy Antilia 2 collided 3 billion years ago | Image courtesy of Sukanya Chakrabarti/Rochester Institute of Technology

Chakrabarti, the lead author of the new study, thinks this discovery would help astrophysics develop methods to monitor dark galaxies, and ultimately solve the mystery of dark matter.

“If Antlia 2 is the dwarf galaxy we predicted, you know what its orbit had to be. You know it had to come close to the galactic disk. That sets stringent constraints, therefore, on not just on the mass, but also its density profile. That means that ultimately you could use Antlia 2 as a unique laboratory to learn about the nature of dark matter,” she said.

Read More: The ESA’s Gaia Mission is Revolutionizing Astronomy

A few years ago, a group of astrophysicists used observational data from the Sloan Digital Sky Survey (SDSS) to find that the Milky Way’s galactic disc is corrugated. They identified four separate structures, like ripples, evenly spaced lying roughly 6,000 light-years one from the other.

Image representation of Milky Way's ripple effect that's allegedly caused by its collision with a dwarf galaxy billions of years ago. | Image courtesy of Dana Berry
Image representation of Milky Way’s ripple effect that’s allegedly caused by its collision with a dwarf galaxy 3 billion years ago. | Image courtesy of Dana Berry

They suggested that this could have been caused by the aftershocks of a past encounter with a dwarf galaxy. Computer simulations render ripples that look like the waves a dwarf galaxy would create if it passed through the Milky Way’s disk”.

Now, the new findings of Chakrabarti and colleagues at RIT give more weight to this hypothesis. And they won’t stop here. The RIT team is waiting for future batches of data from the Gaia mission to see the impact the collision had, not on the Milky Way, but on the dark dwarf galaxy Antlia 2.

Read More: Scientists Discover The Weight Of The Milky Way

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Zayan Guedim

Trilingual poet, investigative journalist, and novelist. Zed loves tackling the big existential questions and all-things quantum.

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