From: Larry Klaes (email@example.com)
Date: Fri May 18 2001 - 15:05:56 PDT
From: firstname.lastname@example.org [mailto:email@example.com]On Behalf Of firstname.lastname@example.org
Sent: Friday, May 18, 2001 11:52 AM
Subject: The Early Universal Web - Comet LINEAR Splits Further
please find below a Press Release about unique observations with the
VLT of a number of very distant objects, seen at a time that
corresponds to about 2 billion years after the Big Bang. They are
found to line neatly up along a "cosmic filament".
The text, images and an accompanying video clip are available at:
We have today also released a new VLT image of Comet LINEAR (C/2001
A2) that recently broke into two pieces. Interestingly, one of these
pieces has split again and there are now three fragments moving
towards the comet's perihelion which will be passed in a week's time.
The comet can be seen with the unaided eye in the southern sky. Look
The ESO EPR Dept.
Information from the European Southern Observatory
ESO Press Release 11/01
18 May 2001 [ESO Logo]
For immediate release
A Glimpse of the Very Early Universal Web
The VLT Maps Extremely Distant Galaxies
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  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
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
PR Photo 19a/01: Web-like structures in the young Universe (computer
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
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 Caption: Computer model of the
19a/01 universe at an age of about 2
billion years (i.e., at redshift 3,
see the text). In the simulated
[Preview - JPEG: 353 x 400 pix - universe gravity causes the
304k] primordial matter to arrange itself
[Normal - JPEG: 706 x 800 pix - in thin filaments, much like a
952k] 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
Astrophysics, Garching, Germany, and
kindly made available for this Press
Release (please be sure to quote the
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 , who have been searching for compact clumps of hydrogen in the
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 A), 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
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")
VLT confirms the predictions
[ESO PR Photo 19b/01] ESO PR Photo [ESO PR Photo 19c/01] ESO PR Photo
[Preview - JPEG: 400 x 276 pix - [Animated GIF: 369 x 369 pix - 67k]
[Normal - JPEG: 800 x 551 pix -
[Hi-Res - JPEG: 3000 x 2067 pix -
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
Already in 1998, the present team of astronomers obtained very deep images
with the ESO 3.58-m New Technology Telescope (NTT) at the La Silla
Observatory (Chile) of the sky field around the quasar Q1205-30. The
redshift of this distant object has been measured as z = 3.04, corresponding
to a look-back time of about 85% of the age of the Universe. Assuming this
to be about 15 billion years, we now observe the quasar as it appeared 13
billion years ago, hence about 2 billion years after the Big Bang.
The images were obtained through a special optical filter that only allows
light in a narrow spectral waveband to pass. The astronomers chose this
wavelength to coincide with that of the Lyman-alpha emission line redshifted
to z = 3.04, i.e. 490 nm in the green spectral region. Lyman-alpha radiation
from objects at the distance of the quasar - and thus, at nearly the same
redshift - will pass through this optical filter. When these images are
combined with other deep images taken through much wider red and blue
filters, the Lyman-alpha emitting objects at redshift 3.04 will show up as
small, intensely green objects, while most other objects in the field will
appear in various shades of red, blue and yellow, cf. PR Photo 19b/01.
The spatial distribution of the galaxies
[ESO PR Photo 19d/01] [ESO PR Photo 19e/01] [ESO Video Clip 04/01]
Caption: PR Photo 19d/01 Pshows the distribution of the observed LEGOs
(the hexagons); the three space co-ordinates being determined by the
position in the sky and the distance (from the measured redshift, see
the text). They are clearly located along a rather narrow filament,
here indicated by a hollow cylinder seen from the front (left) and
from the side (right). The surrounding box is drawn to facilitate the
3-D comprehension - it measures approximately 8.8 x 8.8 x 13.3 million
light-years. PR Photo 19e/01 provides another view of the filament
from a different angle, as well as an artist's impression (in colour).
The eye represents the viewing angle of the telescope, see also PR
Photo 19c/01. PR Video Clip 04/01 provides an animated view of the
spatial configuration of the filaments and the observed objects.
Thanks to the great light-gathering capabilily of the VLT and the excellent
FORS1 multi-mode instrument at the 8.2-m ANTU telescope, spectra of eight,
faint Lyman-alpha objects were obtained in March 2000 that allowed measuring
their exact redshifts and hence, their distances . When two co-ordinates
from the position in the sky were combined with the measured redshifts into
a three-dimensional map, the astronomers found that all of the objects lie
within a thin, well-defined filament, cf. PR Photos 19d/01 and 19e/01.
Speaking for the group, Palle Moeller is exhilarated: "We have little doubt
that for the first time, we are here seeing a small cosmic filament in the
early universe. At this enormous distance and correspondingly long look-back
time, we see it at a time when the universe was only about 2 billion years
old. This is obviously in agreement with the predictions by the computer
models of a web-like structure, lending further strong support to our
current picture of the early development of the universe in which we live".
Implications of this discovery
Does this observation change our view of the early universe? No - on the
contrary, it confirms the predictions of computer-models about how cosmic
structures formed in the early days after the Big Bang.
The most important ingredient in the cosmological models is the dark matter
that is believed to contribute about 95% of the mass of the universe. The
present confirmation of the predictions of the models therefore also
indirectly confirms that it is the dark matter that controls the formation
of structures in the universe.
However, there is still a long way to go before it will be possible to make
a more detailed comparison between observations and predictions, e.g., from
PR Photo 19e/01 to PR Photo 19a/01! Asked about what they consider the most
important consequence of their observations, the team responds: "We have
shown that we now have an observational method with which we may study the
cosmic web in the early universe, and the VLT is a great tool for such
studies. The way forward is now pretty clear - we just have to find those
faint and distant LEGOs and then do the spectral observations from which we
may determine how they are distributed in space".
The research described in this press release is the subject of a scientific
article by the team, "Detection of a redshift 3.04 filament", to appear as a
Letter to the Editor in the European journal Astronomy & Astrophysics.
 The team consists of Palle Moeller, Johan Fynbo (both at ESO, Garching)
and Bjarne Thomsen (Institute of Physics and Astronomy, Aarhus, Denmark).
 In astronomy, the redshift denotes the fraction by which the lines in
the spectrum of an object are shifted towards longer wavelengths. The
observed redshift of a distant hydrogen cloud or galaxy gives a direct
estimate of the apparent recession velocity as caused by the universal
expansion. Since the expansion rate increases with the distance, the
velocity is itself a function (the Hubble relation) of the distance to the
object. The higher the redshift of an object, the more distant it is and the
longer is the look-back time, i.e. the earlier is the corresponding epoch.
 See also ESO Press Release 13/99 and ESO Press Release 08/00 (Report F).
Technical information about the photos
PR Photo 19b/01 is a colour composite, based on three images. The green
channel is based on images with a total exposure time of 17.8 hours,
obtained through a 2 nm wide, optical filter, centred at wavelength 490.6 nm
and obtained in 1998 with the SuSI2 instrument at the ESO 3.58-m New
Technology Telescope (NTT) on La Silla. The blue and red channels are based
on 13 400-sec exposures in a B-filter and 15 250-sec exposures in an
I-filter, respectively, both obtained with 8.2-m VLT ANTU telescope and the
multi-mode FORS1 instrument. The field measures 3.0 x 1.8 arcmin2. North is
up and East is left. PR Photo 19c/01 is based on 13 400-sec exposures in a
B(lue) optical filter, obtained with VLT ANTU and the multi-mode FORS1
instrument in March 2000. The seeing was 0.7 - 1.0 arcsec and the field
measures 6.8 x 6.8 arcmin2. North is up and East is left.
European Southern Observatory
Garching near Munich, Germany
European Southern Observatory
Garching near Munich, Germany
Institute of Physics and Astronomy
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