Posted on 03/09/2004 11:11:27 AM PST by alnitak
Hubble's deepest view ever unveils earliest galaxies
SPACE TELESCOPE SCIENCE INSTITUTE NEWS RELEASE
Posted: March 9, 2004
Astronomers at the Space Telescope Science Institute today unveiled the deepest portrait of the visible universe ever achieved by humankind. Called the Hubble Ultra Deep Field (HUDF), the million-second-long exposure reveals 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 new image should offer new insights into what types of objects reheated the universe long ago.
 This view of nearly 10,000 galaxies is the deepest visible-light image of the cosmos. Called the Hubble Ultra Deep Field, this galaxy-studded view represents a "deep" core sample of the universe, cutting across billions of light-years. Credit: NASA, ESA, S. Beckwith (STScI) and the HUDF Team Download a larger image here |
"Hubble takes us to within a stone's throw of the big bang itself," says Massimo Stiavelli of the Space Telescope Science Institute in Baltimore, Md., and the HUDF project lead. The combination of ACS and NICMOS images will be used to search for galaxies that existed between 400 and 800 million years (corresponding to a redshift range of 7 to 12) after the big bang. A key question for HUDF astronomers is whether the universe appears to be the same at this very early time as it did when the cosmos was between 1 and 2 billion years old.
The HUDF field contains an estimated 10,000 galaxies. In ground-based images, the patch of sky in which the galaxies reside (just one-tenth the diameter of the full Moon) is largely empty. Located in the constellation Fornax, the region is below the constellation Orion.
The final ACS image, assembled by Anton Koekemoer of the Space Telescope Science Institute, 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.
 These close-up snapshots of galaxies in the Hubble Ultra Deep Field reveal the drama of galactic life. Credit: NASA, ESA, S. Beckwith (STScI) and the HUDF Team Download a larger image here |
The NICMOS sees even farther than the ACS. The NICMOS reveals the farthest galaxies ever seen, because the expanding universe has stretched their light into the near-infrared portion of the spectrum. "The NICMOS provides important additional scientific content to cosmological studies in the HUDF," says Rodger Thompson of the University of Arizona and the NICMOS Principal Investigator. 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). Thompson must confirm the NICMOS discovery with follow-up research.
"The images will also help us prepare for the next step from NICMOS on the Hubble telescope to the James Webb Space Telescope (JWST)," Thompson explains. "The NICMOS images reach back to the distance and time that JWST is destined to explore at much greater sensitivity." In addition to distant galaxies, the longer infrared wavelengths are sensitive to galaxies that are intrinsically red, such as elliptical galaxies and galaxies that have red colors due to a high degree of dust absorption.
The entire HUDF also was observed with the advanced camera's "grism" spectrograph, a hybrid prism and diffraction grating. "The grism spectra have already yielded the identification of about a thousand objects. Included among them are some of the intensely faint and red points of light in the ACS image, prime candidates for distant galaxies," says Sangeeta Malhotra of the Space Telescope Science Institute and the Principal Investigator for the Ultra Deep Field's ACS grism follow-up study. "Based on those identifications, some of these objects are among the farthest and youngest galaxies ever seen. The grism spectra also distinguish among other types of very red objects, such as old and dusty red galaxies, quasars, and cool dwarf stars."
Galaxies evolved so quickly in the universe that their most important changes happened within a billion years of the big bang. "Where the HDFs showed galaxies when they were youngsters, the HUDF reveals them as toddlers, enmeshed in a period of rapid developmental changes," Stiavelli says.
 Illustration Credit: NASA and A. Feild (STScI) Download a larger image here |
Though ground-based telescopes have, to date, spied objects that existed just 500 million years after the big bang (at a redshift of 10), they need the help of a rare natural zoom lens in space, called a gravitational lens, to see them. However, the ACS can reveal typical galaxies at these great distances. Even much larger ground-based telescopes with adaptive optics cannot reproduce such a view. The ACS picture required a series of exposures taken over the course of 400 Hubble orbits around Earth. This is such a big chunk of the telescope's annual observing time that Institute Director Steven Beckwith used his own Director's Discretionary Time to provide the needed resources.
The HUDF observations began Sept. 24, 2003 and continued through Jan. 16, 2004. 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.
Just like the previous HDFs, the new data are expected to galvanize the astronomical community and lead to dozens of research papers that will offer new insights into the birth and evolution of galaxies.
Questions & Answers
1. How faint are the farthest objects?
The Hubble observations detected objects as faint as 30th magnitude. The faintest objects the human eye can see are at sixth magnitude. Ground-based telescopes also can detect 30th-magnitude objects. Those objects, however, are so dim they are lost in the glare of brighter, nearby galaxies.
Searching for the faintest objects in the Ultra Deep Field is like trying to find a firefly on the Moon. Light from the farthest objects reached the Hubble telescope in trickles rather than gushers. The orbiting observatory collected one photon of light per minute from the dimmest objects. Normally, the telescope collects millions of photons per minute from nearby galaxies.
2. How many orbits did it take to make the observations?
It took 400 orbits to make the observations.
3. How many exposures were needed to make the observations?
The Hubble telescope's Advanced Camera for Surveys' wide-field camera snapped 800 exposures, which equals two exposures per orbit. The exposures were taken over four months, from Sept. 24, 2003 to Jan. 16, 2004.
4. How much viewing time was needed to make all the exposures?
The 800 exposures amounted to about 1 million seconds or 11.3 days of viewing time. The average exposure time was 21 minutes.
5. How many galaxies are in the image?
The image yields a rich harvest of about 10,000 galaxies.
6. How many colors (filters) were used to make the observations?
The colors used were blue, green, red, and near-infrared. The observations were taken in visible to near-infrared light.
7. If astronomers made the Hubble Ultra Deep Field observation over the entire sky, how long would it take?
The whole sky contains 12.7 million times more area than the Ultra Deep Field. To observe the entire sky would take almost 1 million years of uninterrupted observing.
8. How wide is the Ultra Deep Field's slice of the heavens?
The Hubble Ultra Deep Field is called a "pencil beam" survey because the observations encompass a narrow, yet "deep" piece of sky. Astronomers compare the Ultra Deep Field view to looking through an eight-foot-long soda straw.
The Ultra Deep Field's patch of sky is so tiny it would fit inside the largest impact basin that makes up the face on the Moon. Astronomers would need about 50 Ultra Deep Fields to cover the entire Moon.
9. How sharp is Hubble's resolution in pinpointing far-flung galaxies in the Ultra Deep Field?
Hubble's keen vision (0.085 arc seconds.) is equivalent to standing at the U.S. Capitol and seeing the date on a quarter a mile away at the Washington monument.
Mother Nature's canvass in the heavens !
Same general direction perhaps but the all around space between all these objects is expanding at a high rate of speed as well.
I guess what I'm trying to say is the lateral distance is increasing as well. So, to simplify it... If you had two objects going in the same general direction (i.e.- That Way), the distance between the two would increase even though they continued going generally 'that way'.
I guess, think about two highways that start at the same place and run roughly parallel at first and are headed in seemingly the same direction. If you were driving in a car on one highway and your neighbors were driving in a car on the other one and you were both driving the same speed, for a while it would probably not even seem like you were moving in relation to one another.
But if the 'side by side' distance between those two highways increased by only a little bit per mile, after a while you would be able to note that the other car was moving still towards the west coast (for example) but more and more away from you and your family (laterally). If this continued eventually the other car would be far off in the distance, even though still moving generally west. They could even be doing the same speed as you to start with but as this lateral disparity in distance increased, you would note an acceleration away from your own position. This would give you the red shift.
You see what I mean?
That's roughly a two dimensional model. With an explosion or the Big Bang, you would have that phenomenom happening in 3 dimensions.
Now, I realize this begs the question- what about people driving on the same highway with you? ;-) But think about this- in the three dimensions plus Time of a rapidly expanding space/universe- those cars travelling on the exact same path as you would only represent one very tiny point in the heavens (if you would find it at all). Even very tiny disparities in trajectory would add up very quickly and produce the red shift. Given several billion years it would become very marked indeed, thus you would measure a red shift in everything you saw.
That's the way I see it anyway.
Thay are flying away from the point of the blast at ~c, the speed of light, so all you'll be able to see is the stuff in the flat shell section you are in. You don't look back towards the blast point, you look out anywhere within the expanding shell. It looks flat and you'll only see part of the shell, because c always travels at the same speed and always looks like it does.
You'll never see Earth, because that's you. There are no mirrors out there. You'll just see the other lil-bits. One's that are far away look like they did when the blast happened, because the light from them took distance/c secs(years) to get to you and the time since the blast is approximately a little less than that.
If you look into empty space there's a light all around, coming from everywhere far away in the shell that is the red shifted glow from the initial blast intensity. THat's called the 3oKelvin(-273oC) background radiation from the blast. It's redshifted, because the speed of light must appear as a constant. To do that the frequency shifts to lower wavelengths. It's so far away, the time so long, that the light that used to be a very high frequency now looks super low, from an intensely cold source , almost absolute zero. It's like hearing a Harley engine as the rider flies off into the distance, the music from the engine goes to lower and lower octaves.
Since redshifts mean lower frequencies, time out there-far away looks like it is slowing to a near stop. Eventually all that stuff will hang out there in ever slowing motion, until it fades into the background radiation.
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