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The Puzzling Galaxy at the Edge of Time and Space

Early galaxies were supposed to be primitive, but A1689-zD1 is having none of that.

by Becky Ferreira
Mar 2 2015, 4:00pm

One of the basic wonders of astronomy is the ability to explore deep time alongside deep space. When telescopes capture light from very remote objects, they are also producing a snapshot of a distant, bygone past, which often contradicts what astronomers expect to see in the universe's infancy.

Case in point: A study published today in Nature describes a galaxy called A1689-zD1, one of the youngest and most remote galaxies ever imaged. The study's authors, led by astrophysicist Darach Watson of the University of Copenhagen, captured the galaxy as it was when the universe was only about 700 million years old—about 12.8 billion years ago.

This galaxy is so distant that it would have been invisible without the gravitational lensing effects of a large galaxy cluster called Abell 1689, located nearly 2.2 billion light years away in the constellation Virgo. The cluster's enormous mass acts as a natural telescope by bending and amplifying light from objects behind it, like A1689-zD1.

The young galaxy appears over nine times larger than it would without this handy magnification, allowing Watson's team to perform spectral analysis on it with the VLT (Very Large Telescope) and ALMA (Atacama Large Millimeter/submillimeter Array). It is still barely visible in the below image, but the light that did make it through was full of surprises.

A1689-zD1 in multiple wavelength treatments. Credit: NASA; ESA; L. Bradley (Johns Hopkins University); R. Bouwens (University of California, Santa Cruz); H. Ford (Johns Hopkins University); and G. Illingworth (University of California, Santa Cruz)

The team's expectation was that A1689-zD1 would be a more primitive, metal-poor galaxy given its early stage of development. In much the same way that life on Earth began with limited ingredients and evolved into more complex forms, each stellar generation forges elements heavier than hydrogen and helium, which form the building blocks of the following generation. Accordingly, the universe's very first batch of galaxies is supposed to be pretty basic.

But interestingly, A1689-zD1 appears to be (or to have been) a very mature galaxy, enriched with heavy metals and sporting a dust-to-gas ratio similar to the Milky Way.

That's important because interstellar dust is the cosmic dough from which planets and stars are formed. The fact that this incredibly young galaxy was already awash with dust and metals suggests that the early universe may have contained chemically lush worlds similar to those in our own solar system. It also raises questions about the development of galaxies in the universe's hazy early days.

"This amazingly dusty galaxy seems to have been in a rush to make its first generations of stars," said co-author Kirsten Knudsen in a statement. "In the future, ALMA will be able to help us to find more galaxies like this, and learn just what makes them so keen to grow up."

Galaxies aren't the only objects that appear to have grown up fast at cosmic dawn. Just last week, Motherboard reported on the discovery of the most luminous quasar and most massive black hole ever discovered in the early universe, which baffled cosmologists for precisely the same reasons that make A1689-zD1 such an anomaly.

"There are natural limits of how rapid a black hole can grow and how early they can grow," cosmologist Xiaohui Fan, a co-author on the quasar paper, told Motherboard last Wednesday. "The fact that this object is so massive and so early means we might have to adjust our models of how these natural limits work."

The same could be said for A1689-zD1's surprising maturity despite its fledgling age. It seems that the further we reach into these murky early years, the more these early objects defy expectation with their puzzling complexity. Perhaps the Milky Way's most ancient galactic ancestors were not the throwbacks they were once made out to be.