Weird Ancient Spiral Galaxy Discovered
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- Newly found spiral galaxy predates previously known spirals by about 2 billion years.
- The ancient galaxy is swallowing an intruder galaxy, which may be causing the spiral structure.
- The spiral's rotating disk and arms may last just 100 million years.
Astronomers have discovered a three-armed spiral galaxy dating back nearly 11 billion years -- much older than similarly structured objects that are common in the modern universe.
The discovery was so jarring, scientists at first didn't believe their data.
"Our first thought was that we must have the wrong distance for the galaxy," lead researcher David Law, with the University of Toronto, told Discovery News.
"Then we thought perhaps it was the human brain playing tricks on us. If you look at enough blobby, weird-looking galaxies sooner or later, like a Rorschach blob test, you start to pick out patterns whether or not they're there," Law said.
Follow-up observation, however, showed that the galaxy, known as Q2343-BX442 and located in the direction of the Pegasus constellation, was not a mass of clumpy galaxies, but indeed a regular, rotating, spiral disk galaxy, albeit a thicker and puffier rendition of modern day spiral galaxies, such as the Milky Way.
The Hubble Space Telescope was used to image the galaxy's spiral structure, but to prove the spirals were indeed rotating, the researchers used the Keck II telescope in Hawaii to study the object's internal motions.
"It was shocking," said astronomer Alice Shapley, with the University of California, Los Angeles. "At redshift 2, where we found this galaxy, there hadn't been any other spirals or any other rotating disk galaxies found. We don't know of any other samples like this."
Most galaxies dating back to redshift 2, a cosmic yardstick that equates to about 10.7 billion years old, look lumpy and irregular, without symmetry.
"They're kind of like train wrecks," Shapley told Discovery News.
Out of sample of 306 Hubble Space Telescope images of ancient galaxies, just one -- BX442 -- had this beautiful spiral pattern, she added.
Scientists believe the galaxy's shape is due to gravitational effects of a small intruder galaxy. If that is true, BX442's days as a spiral are numbered.
Computer simulations show BX442, a relatively large galaxy with about the same mass as the Milky Way, would last about 100 million years as a spiral structure, a relative blink in cosmic time.
"We think that we just happened to catch it at a very special time," Shapley said. "I'd say by today, it probably doesn't look like a spiral galaxy."
Other spiral galaxies, like our own Milky Way, are longer-lived.
"One of the leading mechanisms that we believe explains modern day spirals, such as the Milky Way, is what is called 'density wave theory,' which doesn't need any kind of nearby galaxy. It happens from the disk alone in isolation," Law said.
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But several of the most eye-popping spirals, such as Whirlpool Galaxy, have small companions nearby that may be playing in role in shaping the spiral structure.
"The universe is an incredible and beautiful place," Law said. "It keeps offering up surprises when we least expect them."
The research appears in this week's Nature.