Mathematics – Logic
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001eso..pres...11.&link_type=abstract
ESO Press Release, 05/2001
Mathematics
Logic
Scientific paper
The VLT Maps Extremely Distant Galaxies
Summary
New, trailblazing observations with the ESO Very Large Telescope (VLT) at Paranal lend strong support to current computer models of the early universe: It is "spongy", with galaxies forming along filaments, like droplets along the strands of a spiders web.
A group of astronomers at ESO and in Denmark [1] determined the distances to some very faint galaxies in the neighbourhood of a distant quasar. Plotting their positions in a three-dimensional map, they found that these objects are located within a narrow "filament", exactly as predicted by the present theories for the development of the first structures in the young universe .
The objects are most likely "building blocks" from which galaxies and clusters of galaxies assemble.
This observation shows a very useful way forward for the study of the early evolution of the universe and the emergence of structures soon after the Big Bang. At the same time, it provides yet another proof of the great power of the new class of giant optical telescopes for cosmological studies.
PR Photo 19a/01 : Web-like structures in the young Universe (computer model). PR Photo 19b/01 : A group of objects at redshift 3.04 . PR Photo 19c/01 : Animated view of sky field and distant filament . PR Photo 19d/01 : The shape of the filament . PR Photo 19e/01 : Artist's impression of the very distant filament. PR Video Clip 04/01 : Video animation of the very distant filament. The computers are ahead of the telescopes
For the past two decades cosmologists have been in the somewhat odd situation that their computers were "ahead" of their telescopes. The rapid evolution of powerful computer hardware and sophisticated software has provided theorists with the ability to build almost any sort of virtual universe they can imagine. Starting with different initial conditions just after the Big Bang, they can watch such fictional worlds evolve over billions of years in their supercomputers - and do so in a matter of days only.
This has made it possible to predict what the universe might look like when it was still young. And working the opposite way, a comparison between the computer models and the real world might then provide some information about the initial conditions.
Unfortunately, until recently astronomical telescopes were not sufficiently powerful to directly study the "real world" of the young universe by observing in detail the extremely faint objects at that early epoch, and thereby to test the predictions. Now, however, the advent of giant telescopes of the 8-10 metre class has changed this situation and a group of astronomers has used the ESO Very Large Telescope (VLT) at Paranal Observatory (Chile) to view a small part of the early cosmic structure. The telescopes have begun to catch up with the computer simulations. First Structures of the Universe
ESO PR Photo 19a/01
ESO PR Photo 19a/01
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Caption : Computer model of the universe at an age of about 2 billion years (i.e., at redshift 3, see the text). In the simulated universe gravity causes the primordial matter to arrange itself in thin filaments, much like a spider's web. The colour coding indicates the density of the gas, yellow for highest, red for medium, and blue for the lowest density. In the high density (yellow) regions the gas will undergo collapse and ignite bursts of star formation. Those small star-forming regions will slowly stream along the filaments. When they meet at the intersections (the "nodes"), they will merge and cause a gradual build-up of the galaxies we know today. In this sense they are the building blocks of which galaxies are made. This simulated image was computed by Tom Theuns at the Max-Planck-Institute for Astrophysics, Garching, Germany, and kindly made available for this Press Release (please be sure to quote the source).
All recent computer-simulations of the early universe have one prediction in common: the first large-scale structures to form in the young universe are long filaments connected at their ends in "nodes" . The models typically look like a three-dimensional spider's web, and resemble the neural structure of a brain ( PR Photo 19a/01 ).
The first galaxies or rather, the first galaxy building blocks , will form inside the threads of the web. When they start emitting light, they will be seen to mark out the otherwise invisible threads, much like beads on a string. In the course of millions and billions of years, those early galaxies will stream along these threads, towards and into the "nodes". This is where galaxy clusters will later be formed, cf. ESO PR 13/99. During this process the structure of the universe slowly changes. From being dominated by filaments, it becomes populated by large clusters of galaxies that are still connected by "bridges" and "walls", the last remains of the largest of the original filaments. The Lyman-alpha spectral line
New observations with the ESO Very Large Telescope have now identified a string of galaxies that map out a tight filament in the early universe. This trailblazing result is reported by a team of astronomers from ESO and Denmark [1], who have been searching for compact clumps of hydrogen in the early universe.
Hydrogen was formed during the Big Bang some 15 billion years ago and is by far the most common element in the universe. When stars are formed by contraction inside a large and compact clump of hydrogen in space, the surrounding hydrogen cloud will absorb the ultraviolet light from the newborn stars, and this cloud will soon start to glow.
This glow is mostly emitted at a single wavelength at 121.6 nm (1216 Å), the "Lyman-alpha" emission line of hydrogen. This wavelength is in the ultraviolet part of the spectrum to which the terrestrial atmosphere is totally opaque. Accordingly, the Lyman-alpha emission can normally not be observed by ground-based telescopes. However, if a very distant hydrogen cloud emits Lyman-alpha radiation, then this spectral line will be red-shifted from the ultraviolet into the blue, green or red region of the spectrum [2].
For this reason, observations with large ground-based telescopes of Lyman-alpha radiation can be used to identify faint objects forming inside the high-redshift filaments. The team refers to such objects as the LEGO-blocks of cosmology ("Lyman-alpha Emitting Galaxy-building Objects") [3]. VLT confirms the predictions
ESO PR Photo 19b/01
ESO PR Photo 19b/01
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ESO PR Photo 19c/01
ESO PR Photo 19c/01
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Caption : PR Photo 19b/01 is a "true-colour" image of part of the sky field near the quasar Q 1205-30 . Red, blue and yellow objects are displayed with their true colours, while objects at a redshift of about 3 and with strong Lyman-alpha emission lines have a bright green colour (see the text). Six Lyman-alpha Emitting Galaxy-building Objects (LEGOs for short) are marked by hexagons. The quasar (at the lower left) is marked by a larger hexagon and is seen to have an extended Lyman-alpha cloud in front of it, here visible as extended green light. In PR Photo 19c/01 , the entire sky field is shown, as observed through the blue filter. The quasar is marked by a red hexagon while the LEGOs are indicated by yellow hexagons. A total of eight objects at redshift 3.04 are identified. One is located in front of the quasar and was found by means of its absorption of the quasar light, while the seven other objects were identified by their Lyman-alpha emission. As explained in the text, all these objects are found to lie inside a thin filament, here visualized in an animated GIF-display. Almost all of the other objects seen in this deep image are either stars in the outskirts of our own Milky Way galaxy or faint galaxies lying between us and the distant filament. Technical information about these photos is available below.
Already in 1998, the present team of astronomers obtained very deep ima
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