A Trick of Perspective
In 1999, two astronomers from the University of Alabama were scanning the sky for overlapping galaxies when they found this intriguing object, subsequently named NGC 3314. It looks as if the two spiral galaxies are smashing into each other in swirling gravitational frenzy, but in fact they’re actually separated by tens of thousands of light-years—they just happen to be stunningly aligned from our vantage point. The pinwheel galaxy in the foreground (NGC 3314A) is 117 million light-years away, and the galaxy in the background (NGC 3314B) is 140 million light-years away, both in the constellation of Hydra. Even if we didn’t know how far apart they are, we could still tell they’re physically independent—interacting galaxies are usually obvious because the enormous gravitational forces involved in such collisions warp and change the galaxies’ shapes. Though the pinwheel galaxy does look a bit deformed, especially in the streams of white-blue stars at the bottom right, that’s probably due to an encounter with a much closer galaxy. This chance alignment isn’t just an interesting bit of celestial trivia, though. It gives astronomers a unique chance to study the dark material in the foreground pinwheel galaxy. The glow of the background galaxy silhouettes these swirling lanes of interstellar dust, making them more prominent, while the glow of the foreground galaxy makes the background galaxy’s dust look faded. Astronomers can use this to study the properties of the interstellar dust, as well as study gravitational microlensing—the phenomenon where a foreground object bends the light of a background object, allowing the study of objects that faint or emit little light. Images like these are fascinating in a broader sense, too, reminding us of what a limited and yet utterly unique vantage point we occupy in the universe.
(Image Credit: APOD/NASA)