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Part of Hubble Ultra Deep Field

A couple of posts ago I reminded myself  not just of how small and insignificant our own earthly world is, but also of the same being valid for what seems is our gigantic sun - when compared to other stars. A day later Orion Magazine brought home (again) another perspective, one in which even those comparative stars shrink into insignificance. In his article Window of Possibility, Anthony Doerr talked about why the Hubble Ultra Deep Field is the most incredible photograph ever taken. But before talking about that image, let’s start close to home.

While the Sun might represent 99.9% of all the mass in our solar system, it is not only absolutely minute in comparison to some other stars but even more insignificant in relation to our own galaxy. First of all, it is only one amongst 100 billion other suns that inhabit the Milky Way, a figure that seems to make our galaxy enormous. And here’s another one: to circle around its centre, it takes our solar system 230 million years. But despite the immensity of our galaxy, it itself is only one in probably 125 billion galaxies making up our universe, and it certainly is not the biggest. It seems hard to really comprehend those numbers, and Doerr therefore suggests the following comparison: let’s assume there are ‘only’ 100 billion galaxies, each containing 100 billion stars. If we divide all stars in all galaxies by the current number of people on our planet and allow each person to name each star within his of her share at the rate of each individual’s heartbeat, it would take each of us 375 lifetimes to complete the task. I didn’t check that number, but it sounds pretty convincing.

Hubble Ultra Deep Field - Observation depth

Looking at the number of stars and galaxies (leave alone all the other objects, like other planets) is one way to gain some faint understanding of where we really are within this universe (and there are theories predicting that ours is just one of many). Another way of seeing our own place within this gigantic form of existence is to look at time. Our solar system is seen as being roughly 4.6 billion years old. The universe itself has an estimated age of more than 13 billion years (since it probably came into existence in the so-called big bang). A few years ago, over a period from September 3, 2003 through January 16, 2004, we managed through the Hubble Space Telescope to capture light that roughly took those 13 billion years to reach us. 800 exposures taken over the course of 400 Hubble orbits around Earth with a total exposure time of 11.3 days for the ACS and 4.5 days for the NICMOS on-board systems, a composite image called the Hubble Ultra Deep Field, or HUDF, was created from the accumulated data. It was the deepest visible light image of the universe ever taken when looking back in time to reveal the first galaxies to emerge from the so-called “dark ages”, the time shortly after the big bang when the first stars reheated the cold, dark universe.

The image represents a small region of space in the constellation Fornax, a patch of sky smaller than a grain of sand held at arm’s length, and equal to roughly one thirteen-millionth of the total area of the sky. It was chosen because it had a low density of bright stars in the near-field. Although most of the targets visible in the Hubble image can also be seen at infrared wavelengths by ground-based telescopes, Hubble is the only instrument which can make observations of these distant targets at visible wavelengths.

The HUDF of this minute patch of the past universe contains an estimated 10,000 galaxies. The final ACS image is studded with a wide range of galaxies of various sizes, shapes, and colors. In vibrant contrast to the image’s rich harvest of classic spiral and elliptical galaxies, there is a zoo of oddball galaxies littering the field. Some look like toothpicks; others like links on a bracelet. A few appear to be interacting. Their strange shapes are a far cry from the majestic spiral and elliptical galaxies we see today. These oddball galaxies chronicle a period when the universe was more chaotic. Order and structure were just beginning to emerge. The telescope’s ACS camera, the size of a phone booth, captured ancient photons of light that began traversing the universe even before Earth existed. Photons of light from the very faintest objects arrived at a trickle of one photon per minute, compared with millions of photons per minute from nearer galaxies.

The NICMOS sees even further than the ACS. The NICMOS reveals the furthest galaxies ever seen, because the expanding universe has stretched their light into the near-infrared portion of the spectrum. The ACS uncovered galaxies that existed 800 million years after the big bang (at a redshift of 7), but the NICMOS may have spotted galaxies that lived just 400 million years after the birth of the cosmos (at a redshift of 12), almost 9 billion years before our solar system came into existence.

Where are we in this context? To get a more experiential perspective, let’s follow Doerr’s suggestion and take ourselves out to a field some evening after everyone else is asleep. At arrival, let’s first think of what is beneath your feet: the teeming microscopic worlds, soil enriched with “galaxies of bacteria”. Being focused so much on our own species, we tend to miss the vast richness that makes up the fabric of life already here on our planet - so let us allow that awareness to sink in and take a foothold in our consciousness. Then let’s lift up our eyes to look at the night sky - remember the number of heartbeats and lifetimes it would take every human being on Earth to name every star in the universe? Recall the age of the universe, the time it took for light from the first galaxies to reach us today and think of how young we are in comparison as a species: 200,000 years (homo sapiens), which equates to roughly one 67.000th of the age of the universe. Begin to realise that what you are seeing there as billions of tiny points of light is actually the past flying towards you at the speed of light, while at the same time these gigantic galaxies, that appear to our naked eye just as small stars, move away from us at hundreds of miles per second in an ever expanding universe. We are ‘gazing into history [and] staring into the limits’ of our own comprehension and understanding.

“To sense that behind anything that can be experienced,” Einstein once said, “there is a something that our mind cannot grasp and whose beauty and sublimity reaches us only indirectly and as a feeble reflection, this is religiousness.” And Doerr adds: “Whatever we believe in - God, children, nationhood -nothing can be more important than to take a moment every now and then and accept the invitation of the sky: to leave the confines of ourselves and fly off into the hugeness of the universe, to disappear into the inexplicable, the implacable, the reflection of that something our minds cannot grasp.”

This high-resolution image of the HUDF includes galaxies of various ages, sizes, shapes, and colors. The smallest, reddest galaxies, about 100, are some of the most distant galaxies to have been imaged by an optical telescope, existing when the universe was just 800 million years old.

[Thanks to Wikipedia, Observatorio ARVAL and Orion Magazine]

This entry was posted on Monday, July 30th, 2007 at 12:48 am and is filed under natural sciences. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.