Adam Frank for McGraw-Hill

It was a brilliantly simple idea and like many simple ideas, it worked better than anyone had a right to hope. In its wake, astronomers have been given their deepest view ever into the Universe's dim galactic past.

Getting a chance to use a big research telescope is not easy. There are far more astronomers who want to use high-power telescopes than there is time available. When the instrument in question is the Hubble Space Telescope, the time crunch gets that much more severe. Almost every astronomer would love a few hours to play with the world's most renown space-based telescope. Each year they get their chance to ask nicely, sending in hundreds of proposals that are reviewed and, for the most part, rejected. The HST is a valuable commodity and only the best, most worthwhile observation ideas can be given time. The squeeze means that many other great ideas simply have to end up in the "No" pile.

The time squeeze is not, however, a problem for the director of the Space Telescope Science Institute (StSci), the research facility in Baltimore that runs the HST. Each year the director gets a chunk of discretionary time that can be given to whatever special projects he or she thinks is worthwhile. In the astronomical world that is real power. With that in mind you can imagine the potential for uproar when Bob Williams, StSci's director in 1995, decided to use his discretionary time to try something risky and seemingly foolhardy. He pointed HST at a particularly dark, uninteresting patch of sky and then, for nearly 10 days, he left it there with the shudder open.

It was a brilliantly simple idea that paid off in spades. Below is the result of Bob Williams' jump into the unknown - the so-called Hubble Deep Field. For almost 10 consecutive days the HST kept returning to focus on this dark speck of sky only 1/30th the area taken up by the full moon. By leaving the shudder open for so long, light particles (photons) from objects a million times dimmer than what can be seen with the naked eye could slowly collect on the telescopes detector. After 10 days enough of those photons had been collected to form an image of the Universe 11 billion light years away.

On first glance the Hubble Deep Field doesn't seem so amazing. "Big deal" a person might say, "All I see is a bunch of stars". The response to this objection is so simple it raises the Deep Field into the rarified regions of truly ground-breaking science. All the little dots in the Hubble Deep Field image are galaxies not stars. When looked at with HST's high-powered eyes, this seemly unimportant little keyhole of night sky turns out to be full of galaxies. Every one of those galaxies contains about one hundred billion stars. Better still, there is no reason to think that this little blip of sky is any different from any other. The Universe is full of galaxies.

All those galaxies and all those stars…it makes the possibilities for life seem pretty staggering. That alone would seem to justify Bob Williams' gamble. The Hubble Deep Field was truly historic for another reason though. By seeing so far out in space we are also seeing far back in time too. The Deep Field allows us to see back to a moment in celestial history when the Universe was just a fraction of its current age. The relative youth of the cosmos is all too apparent in its galaxies. A detailed look at the galaxies in the Deep Field shows that many of them look like a mess without the classic spiral or elliptical shape we see in nearby and hence older galaxies. The reason for the mess seems clear. The Deep Field's galaxies appear irregular because they are still being assembled! The HST has taken us so far back in time that the age of galaxy formation has not yet ended and the raw materials of gas and dust are still being gathered by gravity into proto-galactic blobs. No one had ever seen this before.

It was a brilliantly simple idea. Point the HST at a dark patch of sky and leave the shudder open. Years from now historians will wonder at the foresight of the scientists involved and marvel at the simple image which forever changed our view of the Universe we were born to.

Points to Ponder

1. The Hubble Deep Field shows the time when galaxies were being built. If you could look further back in time would you be able to see anything? Would there be structures to "see" at all?
2. Could astronomers use the Deep Field to calculate the total number of galaxies in the Universe? If so, how could they do it?
3. What objections do you think a skeptic might have given to keep Bob Williams from going forward with his plan?

Check Out These Web Links

Hubble Images of Distant Galaxies
http://oposite.stsci.edu/pubinfo/distantgalaxies.html

The Hubble Project
http://hubble.gsfc.nasa.gov/

The Hubble Deep Field
http://oposite.stsci.edu/pubinfo/pr/1996/01.html