Not Turtles

There’s a story out there, written about by astronomer Stephen Hawking, but well-known to astronomers from several sources about one person’s rather interesting view of cosmology. It goes as follows.

A well-known scientist (some say it was Bertrand Russell) once gave a public lecture on astronomy. He described how the earth orbits around the sun and how the sun, in turn, orbits around the center of a vast collection of stars called our galaxy. At the end of the lecture, a little old lady at the back of the room got up and said: “What you have told us is rubbish. The world is really a flat plate supported on the back of a giant tortoise.” The scientist gave a superior smile before replying, “What is the tortoise standing on?” “You’re very clever, young man, very clever,” said the old lady. “But it’s turtles all the way down!” (taken from Wikipedia).

While space really isn’t turtles all the way down, it is more like galaxies all the way out, just about (but not quite) as far as we can see. This isn’t a surprise now that astronomers can see literally almost to the “edge” of creation (and there isn’t an edge in space, so I’m speaking poetically here). But, up until the advent of long, deep surveys of space (where astronomers spend gobs of time training specially instrumented telescopes at the sky to see farther and fainter), astronomers weren’t quite sure what they would find at great distances.

As it turns out, they find star formation beginning a few hundred galaxies and galaxy formation that seems to have started in earnest only a few hundred million years after the Big Bang. That’s pretty much in the infancy of the universe, which is about 13.7 billion years old.

So, what do these early galaxies look like? In some images, they look like little shreds of light, not yet fully formed into the distinctive spiral and elliptical shapes we are more familiar with in recent cosmic history. As time goes by, they coalesce into more detailed structures.

Astronomers in the United Kingdom have been using an infrared telescope on Mauna Kea, Hawai’i to look back into time and study galaxies as they appeared about 2.5 billion years ago. They looked at an area of the sky about the size of the full Moon and produced an image of more than 100,000 galaxies. The image below shows their cosmic zoom. The bluish galaxies in the foreground are relatively nearby; what you want to pay attention to are the little reddish dots in the background. THOSE are the very distant galaxies they are studying. So, this image is, as Dr. Sebastiaen Foucaud of University of Nottingham said today, giving astronomers a chance to do a little time travel. “I would compare these observations to the ice cores drilled deep into the Antarctic,” said Dr Foucaud. “Just as they allow us to peer back in time, our ultra-deep image allows us to look back and observe galaxies evolving at different stages in cosmic history, all the way back to just 1 billion years after the Big Bang”.

Sebastien and others are using images like this to understand when the rarest, most massive galaxies form during the early history of the universe. This is a question that they are only now even starting to be able to answer. “We see galaxies 10 times the mass of the Milky Way already in place at very early epochs. Now, for the first time, we are sampling a large enough volume of the distant universe to be able to see them in sufficient numbers and really pin down when they were formed.”

The thing to remember here is that this cosmic “ice core” samples only one spot in the cosmos. Since galaxies are pretty much spread out in all directions (“isotropically” as the scientists say), you could take similar cores in any direction of the sky and see a backdrop of galaxies. So, while it may not be turtles all the way out, it clearly is galaxies stretching out across the universe to its infancy. Before that? The Big Bang and the Dark Ages, two other epochs of cosmic history that astronomers and cosmologists are studying as well.

Here’s more to read about this new result.