Soap Bubbles and Voids
As noted in the preceding section, the distribution of luminous matter in the
Universe has the character of soap bubbles and filaments. The following
figure illustrates further.
The voids and
"walls" that form the large-scale structure are mapped here by more than
100,000 galaxies.
(The faint radial spokes in this figure represent
incomplete sampling in the survey, not true gaps in the distribution of galaxies.)
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The 2dF Spectrograph
The 2dF Spectrograph has a field of view that spans 2 degrees (4 times the diameter of the
full Moon). This is the broadest view of any large telescope.
The 2dF can survey 400 galaxies at once by using a robot arm to place
each of
400 optical fibers precisely in the right position to collect light from a single galaxy
and pipe it to the spectrograph. Every hour the robot positions the fibers to collect
the telescopic images of 400 new
galaxies so that
in a single night of observing the distances to more than 3000 galaxies can be
recorded.
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2dF Redshift Survey
The survey of galaxies illustrated in the preceding figure was
produced by British, Australian, and U. S. astronomers and is
termed the
2dF Galaxy Redshift Survey.
Each dot is a galaxy. Our galaxy
is at the center of the figure. The radial direction represents redshift and therefore,
by the Hubble law, distance.
The angles represent direction on the sky.
The 2dF survey covers about 1/20th
of the whole sky to a depth of more than 4 billion light years. It is made
possible by a new instrument, the
Two Degree Field (2dF) Spectrograph of the
Anglo-Australian Telescope in New South Wales, Australia.
As explained in the adjacent box, this instrument
is capable of determining the
distances to thousands of different galaxies for each complete night of observing.
A Million Galaxies
The 2dF survey catalogued the distance and direction of more than 220,000 galaxies.
This is about a factor of ten more than obtained in the most ambitious surveys
of the preceding decade.
Another survey, the
Sloan Digital Sky Survey, follows on the heels of the 2dF survey
and hopes to catalogue the distances and directions for one million galaxies
over a period of five years.