Galaxy Mergers Archives

February 13, 2023February 13, 2023 by Evan Gough

Astronomers Uncover Mass Migration of Stars into Andromeda

Astronomers at NSF’s NOIRLab found new evidence for a mass immigration of stars into the Andromeda Galaxy. This image shows individual stars from blue (moving toward us) to red (moving away from us). Image Credit: KPNO/NOIRLab/AURA/NSF/E. Slawik/D. de Martin/M. Zamani

Astronomers know that galaxies grow over time through mergers with other galaxies. We can see it happening in our galaxy. The Milky Way is slowly absorbing the Large and Small Magellanic Clouds and the Sagittarius Dwarf Spheroidal Galaxy.

For the first time, astronomers have found evidence of an ancient mass migration of stars into another galaxy. They spotted over 7,000 stars in Andromeda (M31), our nearest neighbour, that merged into the galaxy about two billion years ago.

November 7, 2022November 7, 2022 by Evan Gough

The Perfect Tidal Tail Connects These two Galaxies Seen by Hubble

This image from the NASA/ESA Hubble Space Telescope shows two of the galaxies in the galactic triplet Arp 248. Image Credit: ESA/Hubble & NASA, Dark Energy Survey/Department of Energy/Fermilab Cosmic Physics Center/Dark Energy Camera/Cerro Tololo Inter-American Observatory/NOIRLab/National Science Foundation/AURA Astronomy; J. Dalcanton

Sometimes it’s tempting to imagine a supernatural hand behind the arrangement of celestial bodies. But the Universe is big, huge even, and nature’s flow presents many fascinations.

So it is with the galactic triplet Arp 248, an arrangement of interacting galaxies that’s both visually and scientifically fascinating.

March 29, 2022March 29, 2022 by Evan Gough

Part of the Milky Way Is Much Older Than Previously Believed

Basic structure of our home galaxy, edge-on view. The new results from ESA's Gaia mission provide for a reconstruction of the history of the Milky Way, in particular of the evolution of the so-called thick disc. Image Credit: Stefan Payne-Wardenaar / MPIA

The Milky Way is older than astronomers thought, or part of it is. A newly-published study shows that part of the disk is two billion years older than we thought. The region, called the thick disk, started forming only 0.8 billion years after the Big Bang.

February 27, 2022February 27, 2022 by Andy Tomaswick

Astronomers see an Enormous Shockwave, 60 Times Bigger Than the Milky Way

Astronomers have a thing for big explosions and collisions, and it always seems like they are trying to one-up themselves in finding a bigger, brighter one. There’s a new entrant to that category – an event so big it created a burst of particles over 1 billion years ago that is still visible today and is 60 times bigger than the entire Milky Way.

October 20, 2021October 20, 2021 by Evan Gough

The Large Magellanic Cloud Stole one of its Globular Clusters

The Milky Way with the Small and Large Magellanic Clouds on the left. Image Credit: ESO/Y. Beletsky. CC 4.0

Astronomers have known for years that galaxies are cannibalistic. Massive galaxies like our own Milky Way have gained mass by absorbing smaller neighbours.

Now it looks like smaller galaxies like the Large Magellanic Cloud have also feasted on smaller neighbours.

June 15, 2021June 15, 2021 by Andy Tomaswick

Rare Triple Galaxy Merger With at Least Two Supermassive Black Holes

One of the best things about that universe is that there is so much to it. If you look hard enough, you can most likely find any combination of astronomical events happening. Not long ago we reported on research that found 7 separate instances of three galaxies colliding with one another. Now, a team led by Jonathan Williams of the University of Maryland has found another triple galaxy merging cluster, but this one might potentially have two active supermassive black holes, allowing astronomers to peer into the system dynamics of two of the universe’s most extreme objects running into one another.

May 12, 2021May 10, 2021 by Paul M. Sutter

Astronomers see a Rare “Double Quasar” in a Pair of Merging Galaxies

Artist's conception of a double quasar. Image credit: ASA, ESA, Joseph Olmsted (STScI)

What’s better than a quasar? That’s right, two quasars. Astronomers have spotted for the first time two rare double-quasars, and the results show us the dynamic, messy consequences of galaxy formation.

February 2, 2021February 2, 2021 by Evan Gough

When Galaxies Collide, Black Holes Don’t Always Get the Feast They Were Hoping for

What happens when galaxies collide? Well, if any humans are around in about a billion years, they might find out. That’s when our Milky Way galaxy is scheduled to collide with our neighbour the Andromeda galaxy. That event will be an epic, titanic, collision. The supermassive black holes at the center of both galaxies will feast on new material and flare brightly as the collision brings more gas and dust within reach of their overwhelming gravitational pull. Where massive giant stars collide with each other, lighting up the skies and spraying deadly radiation everywhere. Right?

Maybe not. In fact, there might be no feasting at all, and hardly anything titanic about it.

February 1, 2021February 1, 2021 by Paul M. Sutter

Galaxy Mergers can Boost Star Formation, and it can Also Shut it Down

It is known today that merging galaxies play a large role in the evolution of galaxies and the formation of elliptical galaxies in particular. However there are only a few merging systems close enough to be observed in depth. The pair of interacting galaxies picture seen here — known as NGC 3921 — is one of these systems. NGC 3921 — found in the constellation of Ursa Major (The Great Bear) — is an interacting pair of disc galaxies in the late stages of its merger. Observations show that both of the galaxies involved were about the same mass and collided about 700 million years ago. You can see clearly in this image the disturbed morphology, tails and loops characteristic of a post-merger. The clash of galaxies caused a rush of star formation and previous Hubble observations showed over 1000 bright, young star clusters bursting to life at the heart of the galaxy pair.

Galaxy mergers are beautiful sights, but ultimately deadly. In the midst of the collision, the combined galaxy will shine brighter than it ever has before. But that glory comes with a price: all those new stars use up all the available fuel, and star formation grinds to a halt.

October 23, 2020October 23, 2020 by Evan Gough

Astronomers Find the Hollowed-Out Shell of a Dwarf Galaxy that Collided With the Milky Way Billions of Years Ago

The Karl Jansky Very Large Array at night, with the Milky Way visible in the sky. Credit: NRAO/AUI/NSF; J. Hellerman

In 2005 astronomers found a dense grouping of stars in the Virgo constellation. It looked like a star cluster, except further surveys showed that some of the stars are moving towards us, and some are moving away. That finding was unexpected and suggested the Stream was no simple star cluster.

A 2019 study showed that the grouping of stars is no star cluster at all; instead, it’s the hollowed-out shell of a dwarf spheroidal galaxy that merged with the Milky Way. It’s called the Virgo Overdensity (VOD) or the Virgo Stellar Stream.

A new study involving some of the same researchers shows how and when the merger occurred and identifies other shells from the same merger.