Hubble Sees Infant Galaxies at the Edge of the Universe

By Phil Plait

Here are two things I love when it comes to astronomy: A truly cool Hubble image and a mystery. When you combine them, well, you’re on to something very cool indeed. And that’s just what I have here for you.

First, the image: A staggeringly deep Hubble photograph showing thousands of galaxies like grains of sand on the beach:

To Hubble's eye, the Universe is filled with galaxies. Click to embigbangenate.

Photo by NASA,ESA, G. Illingworth (University of California–Santa Cruz), P. Oesch (University of California–Santa Cruz; Yale University), R. Bouwens and I. Labbé (Leiden University), and the Science Team

I had to shrink this image a lot to get it to fit here. I strongly urge you get a higher-res version (especially the 3000 x 2400 pixel version). Because see all those dots? Those aren’t stars. Those are galaxies. Thousands of them. Hubble stared at the same spot in the constellation of Ursa Major for hours, and it came up with this phenomenal image.

And what it also found, actually, was a mystery. In the image are four circled blobs, each very red and highlighted on the right; again, you might want to grab the big image to see this better. Here is one of them, called GNDJ-625464314 (I’ll call it GNDJ-625 for short) in detail:

It's galaxies all the way down.

Again, I remind you, nearly everything you see here is a galaxy, a vast collection of billions of stars. GNDJ-625 is circled, and I inset a zoomed-in shot of it in the lower left. It’s a galaxy, as are the three others in the big image. You can tell right away they’re hugely distant; the red color is due to their redshift, caused by their photons losing energy as they fight their way to us against the expansion of the Universe itself (I have a more detailed explanation of this in another article about distant galaxies).

And it turns out all four really are ridiculously far from Earth; GNDJ-625 is something like 13.2 billion light years away. In other words, we’re seeing it when the Universe itself was only about 600 million years old.

Our galaxy is well over 10 billion years old, for comparison. The galaxy in that picture is a wee baby.

Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death from the Skies!

But it’s a loud one. The Spitzer Space Telescope was used to determine how much energy is being emitted by these galaxies, and it turns out they’re bright. Very, very bright, so bright they must be churning out new stars at a prodigious rate, maybe 50 times faster than our own Milky Way galaxy makes stars now. That’s incredibly prolific. GNDJ-625 itself is only about 1/20^th the size of the Milky Way, so those stars, over a billion of them, are crammed pretty tightly together. All those young, hot stars are blasting out radiation, which is why we can see this galaxy at all at such a soul-crushing distance.

This in turn means the galaxies must be growing rapidly, possibly by gravitationally accreting gas, or by merging with other small galaxies. But given their young age, they must have done so at a fantastic rate to get as big and bright as we see them.

And it’s not at all clear how that could happen. It’s also odd that four would be found so close together in the sky; it seems unlikely this would happen. Perhaps it’s a statistical fluke, or perhaps there’s more going on here than we understand at first glance.

But that’s the beauty of probing as far as we can see; we get to test the literal limits of our knowledge, to push the mathematics and physics to see if we can figure out what’s going on. The really interesting stuff tends to loiter at the outer edges of what we can do, and it’s those things that provide so much leverage when we test our hypothesis with them. We have a decent understanding of how galaxies grow to huge size (like our Milky Way) today, but when did they start this journey? How fast did they grow in the past, what material was available to them, how densely packed were the galaxies and the stars within? Was it something inside them to led to this growth, or something in their environment around them? Or both?

These objects will help us figure all that out. The observations here are part of a survey called GOODS, for Great Observatories Origins Deep Survey, specifically designed to look for the faintest galaxies at the most forbidding distances, to find what it could find.

I expect much, much more knowledge will be unearthed in this treasure chest of galaxies. It’s funny to think that in a survey that goes so terribly deep, we’ve only just scratched its surface.