Why Galaxies Snuggling Together Are Bad News for Starbirth

The merging galaxies NGC 7752 (larger) and NGC 7753 (smaller), collectively called Arp 86. Blue and green represent wavelengths of light strongly emitted by stars, while red shows a wavelength mostly emitted by dust.
The merging galaxies NGC 7752 (larger) and NGC 7753 (smaller), collectively called Arp 86. Blue and green represent wavelengths of light strongly emitted by stars, while red shows a wavelength mostly emitted by dust.
(Image: © NASA/JPL-Caltech)

You could say that some relationships are doomed — especially in astronomy. A NASA telescope caught several galaxy pairs that will wither away as they grow too close together, robbing the neighborhood of gas that stars need to form.

NASA's Spitzer Space Telescope took the images to better understand how galaxies merge after getting trapped in each other's gravity, according to a statement from NASA. Merging is a rare process now — only a small percentage of galaxies are about to come together — but it was more common about 6 billion to 10 billion years ago, in the universe's youth. (The universe is estimated to be 13.7 billion years old.)

Studying mergers today helps scientists better understand how galaxies underwent this process earlier in the universe's history, providing insight into how the cosmos evolved. A program called Great Observatories All-sky LIRG Survey (GOALS) has already studied 200 nearby objects, including galaxies under merger.

The merging galaxies NGC 6786 (right) and UGC 11415 (left), collectively called VII Zw 96, from images taken by three infrared channels on the Spitzer space telescope.

(Image: © NASA/JPL-Caltech)

Related: The Infrared Universe Seen by Spitzer Telescope

"One of the primary processes thought to be responsible for a sudden halt in star formation inside a merged galaxy is an overfed black hole," NASA officials said in the statement "At the center of most galaxies lies a supermassive black hole — a powerful beast millions to billions of times more massive than the sun. During a galactic merger, gas and dust are driven into the center of the galaxy, where they help make young stars and also feed the central black hole."

But merging comes at a high cost. As the black hole grows, it produces shockwaves that can ripple through the galaxy and expel gas from of the neighborhood, throwing away needed fuel for stars to be born. At worst, galaxies can lose all the fuel they need to create new stars, dooming the galaxies to fade away as their current stars age and die.

These merging galaxies are together known as Arp 302, as well as VV 340. Blue and green represents wavelengths strongly emitted by stars, while red indicates wavelengths mostly emitted by dust.

(Image: © NASA/JPL-Caltech)

NASA officials said researchers are still trying to understand the relationship between mergers, star formation and black hole activity. GOALS scientists recently used the W.M. Keck Observatory in Hawaii to look for shockwaves emanating from an "active galactic nucleus," which refers to an active and bright object with a hungry supermassive black hole embedded inside, eating gas and other material nearby. This study found few shock signatures, which suggests "the role of active galactic nuclei in shaping galaxy growth during a merger may not be straightforward," NASA officials said.

While merging galaxies glow in infrared light easily spotted by Spitzer, GOALS scientists have also used other space observatories such as the Hubble and Chandra space telescopes and the European Space Agency's Herschel satellite. Several ground-based observatories have also been used for GOALS studies, including the Keck Observatory, the National Science Foundation's Very Large Array and the Atacama Large Millimeter Array.

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