Today, spiral galaxies like our own Milky Way are common throughout the cosmos. But that wasn't the case long ago, when galaxy collisions were much more common, gas raining in from the intergalactic medium fed more dramatic star formation and black holes grew faster than they do now, researchers said.
"The vast majority of old galaxies look like train wrecks," said co-author Alice Shapley of UCLA. "Our first thought was, why is this one so different, and so beautiful?"
To learn more about BX442, the team employed a different telescope, the Keck Observatory atop Hawaii's dormant Mauna Kea volcano. They used a Keck spectrograph to study light emitted from 3,600 targets in and around the Milky Way.
This information confirmed that BX442 is indeed a rotating spiral, and not two disk-shaped galaxies that happened to line up in the image.
"We first thought this could just be an illusion, and that perhaps we were being led astray by the picture," Shapley said. "What we found when we took this spectral image of this galaxy is that the spiral arms do belong to this galaxy; it wasn’t an illusion. It’s rotating and has spiral arms. Not only does it look like a rotating disk galaxy — it really is. We were blown away."
The Hubble and Keck observations also revealed a companion dwarf galaxy residing near BX442. The scientists think the gravitational interaction between the two galaxies may be creating BX442's spiral shape, possibly explaining how it became so different than its galactic contemporaries. (The Milky Way has its own satellite dwarf galaxy, known as Sagittarius, that may help produce its spiral arms.)