The Deepest Portrait of Our Universe Yet
Hubble gives us a new image of the thousands of galaxies that exist in a tiny patch of the sky.
When you look up at the sky at night, all of the stars you see around you are very, very close by, as these things go. Maybe -- maybe -- if you have good eyesight and are in the Southern Hemisphere, you can see the blurry spots of the Large and Small Magellanic clouds, two nearby galaxies. From more northern climes, you might be able to catch a naked-eye glimpse of the Andromeda galaxy, some 2.5 million light years from Earth.
By the standards of the universe, these are the kids next door. In the spaces between them (and behind them) is the rest of the universe, at least 100 *billion* other galaxies (and perhaps many more), whose light is far too faint for us to see. If you could zoom in (way in) on a tiny patch of sky, you would see them -- thousands of them.
And that's what NASA has done, aiming its Hubble Space Telescope at the same spot again and again over the course of the past decade. All told, it looked there for a total of 2 million seconds, producing 2,000 images with its Advanced Camera for Surveys and its Wide Field Camera 3, which allows it to capture near-infrared light.
The result, shown above, is called eXtreme Deep Field, or XDF, and NASA says it is the "farthest-ever" portrait of the universe. It contains around 5,500 galaxies, some of which are one ten-billionth the brightness visible to the human eye. There are spiral galaxies that resemble our own Milky Way, fuzzy red galaxies where stars are no longer being formed (at the time the light left them), and faint young galaxies, not yet fully grown. "The history of galaxies -- from soon after the first galaxies were born to the great galaxies of today, like our Milky Way -- is laid out in this one remarkable image," NASA said in a press release. For the oldest galaxies in the image, the light now reaching us first shone some 13.2 billion years ago, more than 8.6 billion years before Earth even existed.
Perhaps more mind-boggling than the number of objects in the image, or just how far away they are, is what a tiny speck of the night sky they all sit in. An illustration from NASA shows a comparison of the field's area to our moon's (when the moon appears at a size of half the width of a finger held at arm's length):
That's the size. But that's not *where* these galaxies are. For understanding that, NASA has made a video, which shows the spot in the constellations where the patch is (located in the southern sky), and then zooms in until you get to XDF.
The new image covers a region of space that is at the center of NASA's earlier Ultra Deep Field, released in 2004, which was the deepest portrait of the universe at the time. Now, with these new observations, we can see that same piece of the sky ever more closely. Multiply that out in your head across the sky, over the blackness, beyond the visible stars: galaxies and galaxies and galaxies. Billions of them, as far as the mind's eye can see.