Mapping Nearby Galaxies at Apache Point Observatory

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New tool reveals ‘missing’ merging galaxies
Deborah Byrd in SPACE | January 10, 2019

Astronomers see many breathtaking merging galaxies, with their giant tidal streams of stars and unusual shapes. But some normal-looking galaxies might be merging, too. Now astronomers have a new tool to find out.​

Galaxies may take billions of years to fully merge into a single galaxy. As astronomers look outward in space, they can see only “snapshots” of this long merger process. Located 300 million light-years away in the constellation Coma Berenices, these 2 colliding galaxies have been nicknamed The Mice because of the long tails of stars and gas emanating from each galaxy. Otherwise known as NGC 4676, the pair will eventually merge into a single giant galaxy. Image via Wikimedia Commons.

When you think about it – given the vastness of space in contrast to the minuteness of all matter – it’s surprising that galaxies collide and merge at all. Yet they do. Astronomers have known for some time, for example, that our Milky Way galaxy will ultimately merge with the large neighboring Andromeda galaxy, some 4 to 8 billion years from now. And just last week we learned that the Large Magellanic Cloud will is on a collision course with our Milky Way, too. This little galaxy will merge with ours in only 2 billion years, possibly knocking our own solar system out of the Milky Way entirely. In distant space, too, astronomers see and study merging galaxies. On January 9, 2019, at the 233rd AAS meeting in Seattle, Washington, astronomers from the Sloan Digital Sky Survey (SDSS) said they have a new tool to find galaxy mergers that would otherwise be “missing.”

They’re searching for these galaxy mergers in data from a survey called MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), which is part of SDSS. The astronomers said in a statement:

These results show that by going beyond simple searches for merging galaxies based just on how they look, astronomers will now be able find more galaxy mergers than ever before.​

Rebecca Nevin of the University of Colorado is lead author of the new galaxy study, which formed the basis of her Ph.D. thesis at Colorado with astronomer Julie Comerford acting as advisor. Nevin commented:

Merging galaxies are key to understanding galaxy evolution, but finding them can be tricky.​

The astronomers said the beautiful visible features of merging galaxies – the giant tidal streams of stars and unusual shapes – are visible in only a small fraction of those observed. They said some galaxies that don’t appear to be merging may actually be merging, after all.