First Light

First Light

First Light

Bad Astronomy
The entire universe in blog form
Nov. 2 2005 10:37 PM

First Light

Sometimes, I see an image, and it literally raises the hair on the back of my neck.

Phil Plait 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!  

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Take a look at this picture (click it for a higher-res version):

Doesn't look like much, does it? Ah, but like so much in astronomy, appearances can be very deceiving.

The picture is from the Spitzer Space Telescope, an orbiting observatory sensitive to infrared light. Astronomers pointed this formidable instrument into a region of the sky in the constellation Draco, where there is a minimum of stars, galaxies, and dust to obscure any distant objects. The fact that you see so many objects in the image is a testament to how sensitive Spitzer is.

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The top part of the image shows the results of a ten-hour exposure. The image is 6x12 arcminutes across, roughly a fifth by a third the size of the full Moon on the sky. Almost all the objects you see in it are stars and galaxies; the stars are in our own Milky Way Galaxy, and are relatively close, maybe a few thousand light years away. The Galaxies (which look pretty much like stars) are much farther, millions or billions of light years away.

But what you don't see in that top image is what's important.

In any deep image of the sky, the bright objects are of course the easiest to notice. Usually, the astronomers display the contrast in an image such that the bright things are easy to see, and anything faint is set to black. But in this case, the astronomers wanted to see the extremely faint objects. To do this, they masked out the bright objects and then upped the contrast... way up.

What pops out of the image is displayed in the bottom part of the image. The masked foreground objects are obvious enough. But what's that fuzzy, glowing material weaving its way in the background?

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According to the astronomers who took the image, most if not all of that diffuse glow comes from the very first stars ever born in the Universe.

According to current theories, after the Big bang, the material in the expanding Universe was too hot to form stars for quite some time. Finally, after about 200 million years, the gas had cooled enough that gravity's ghostly grip could start to form clumps of matter. Before there were galaxies, before there were "normal" stars, before there were planets, before there was anything except hydrogen, helium, and just a taste of lithium, the first stars coalesced from this miasma. They were monsters, these first-generation stars, with as much as 100 times the mass of the Sun. They were short-lived, too: consuming their fuel at prodigious rates, their life span was a fraction of the Sun's. In a few million years, maybe less, they were doomed to explode as titanic supernovae, forming black holes in their cores. Eventually, galaxies may have coalesced around those black holes, leading to normal stars, planets, and eventually us.

But during their short lives, the light those first stars emitted was blinding. That light sleeted out into the still-young Universe, traveling through space as the space itself expanded, like someone running up the down-escalator. Finally, after billions of years-- billions of years after the stars themselves had blown up-- the light reached Earth, falling into the waiting eye of Spitzer.

The fuzzy web of light in that bottom half of the image may be the first real ghost photo-- the image of light from stars long-since dead, the very first stars ever to appear in our Universe.

That's why I got a chill, why the hair on the nape of my neck stirred. Look at that picture again, and wonder that the light recorded in it had traveled for 13.5 billion years, 98.5% of the age of the Universe itself, across that vast and terrible gulf of space. I got a chill when I first saw the picture, but then a spread of warmth: I'm proud to be human, to be able to see this, to know that we can understand it. We all should be proud. We are the way for the Universe to know itself.

Note added morning of Nov3: As I state in this entry, the results here are not confirmed; the light might be from the first stars, or it might not be. Astronomer Ned Wright has his (strong) doubts, for example, which are stated in a CNN article. Hopefully followup data will shed more light (haha) on this.