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ZL2VAL > SETI 14.05.04 12:59l 137 Lines 7008 Bytes #999 (0) @ WW
BID : D50871ZL2VAL
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Subj: New array to increase range
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Sent: 040514/1047Z @:ZL2AB.#46.NZL.OC #:40391 [New Plymouth] FBB7.00g
From: ZL2VAL@ZL2AB.#46.NZL.OC
To : SETI@WW
Exciting Astronomy with the Allen Telescope Array
By Leo Blitz
Director of the Radio Astronomy Laboratory at UC, Berkeley
posted: 06:30 am ET
13 May 2004
Imagine having a telescope one hundred or even one thousand times more
powerful than any previous telescope.
It might be hard to decide what to look at first, but for astronomers
using the Allen Telescope Array (ATA) for conventional radio astronomy,
it will not be too much of a problem. This new instrument will be the
fourth largest telescope in the world, as gauged by its collecting area.
But its real claim to fame is speed. For surveying the radio sky (a task
necessary for SETI discoveries), the ATA will be almost 1,000 times
faster than the Arecibo telescope, between 20 and 2000 times faster than
the Very Large Array (depending on the scientific program) and 50 times
faster than the Green Bank Telescope (GBT).
Moreover, the ATA will be able to resolve sources - i.e., to see fine
detail - better than either the GBT (by a factor of 10) or Arecibo (by a
factor of 3), and it will have spectral capabilities that simply aren't
available at the other telescopes: it can observe multiple spectral
windows simultaneously within the entire spectrum to which the telescope
is sensitive, a new capability available for the first time on the ATA.
So what will the radio astronomers want to do with this fabulous new
instrument? In broad terms, the flagship science will be to determine
the structure of the local universe, to search for new effects of black
holes, and to seek out the primordial dark matter condensations of the
universe. The ATA will be uniquely capable of discovering new phenomena
related to the transient radio sky, that is, sources that vary in
brightness on time scales of seconds to years. Many of these originate
in processes involving ultramassive black holes in the centers of
galaxies, distant supernova explosions near the edge of the observable
universe, and gamma-ray bursts, the most energetic events in the cosmos.
The telescope will also be a general-purpose radio telescope that will
provide fundamentally new measurements and insights into the density of
the very early universe, the formation of stars, the magnetic fields in
the interstellar medium, pulsars, and a host of other phenomena of deep
interest to astronomers. Let's look at two of the major areas of
astronomical research for the ATA.
The Structure of the Nearby Universe
The forces that generated the density fluctuations in its early history
shaped the large-scale structure of the nearby universe. Since dark
matter, of unknown composition, is the largest mass component of the
universe, it is the effect of forces on the dark matter that provides
most of the observed structure. Mapping out the distribution of galaxies
traces the dark matter distribution, something that cannot be determined
any other way. Attempts to map the distribution of galaxies in the
optical portion of the spectrum have been only partially successful
because the presence of dust in the Milky Way obscures a large fraction
of the sky. Another problem with the optical surveys is that they are
not sensitive to faint, low mass galaxies which are often found first in
surveys of atomic hydrogen (HI) in the radio portion of the spectrum and
then later confirmed using large optical telescopes.
The ATA will make the first all-sky neutral hydrogen (HI) survey of the
local universe, which will provide key information about how the
universe evolved. An all-sky HI survey from Hat Creek will detect the
hydrogen in galaxies similar to that of the Milky Way to distances as
large as 20 times that of the Virgo cluster, the nearest rich cluster of
galaxies. The survey will take three years to complete.
But the survey will also be sensitive to dark galaxies: the earliest
matter concentrations to form. A dark galaxy is one that contains only
atomic hydrogen and dark matter, but no stars. These galaxies are very
difficult to detect with current radio telescopes, but may be quite
common, and may represent the earliest concentrations of dark matter
that have not yet coalesced into galaxies. A high-resolution image of a
typical dark galaxy could be produced at the ATA in 5 minutes, but would
take 10 days of time using the Arecibo telescope. Small dark galaxies
can be detected with the ATA to distances as great as the Virgo cluster,
which is about 20 times farther than the distance to the Andromeda
Galaxy, M31. If these galaxies exist, the ATA will find them.
Black Holes
Black holes are among the most remarkable predictions of General
Relativity, Albert Einstein's theory of gravity. They compress so much
mass into such a small volume that gravity overwhelms all other forces
and nothing, not even light, can escape. The unprecedented ability of
the ATA to find transient radio sources will provide a powerful new
probe of black holes in the universe. We highlight two examples:
1. It is now believed that most nearby galaxies have supermassive
black holes at their centers, with masses between a million and a
billion times that of our Sun. However, the number of such black
holes at higher redshift, that is to say, early in the life of the
universe, is poorly constrained. When a star like the Sun passes
close to a massive black hole, it is ripped apart by its strong
gravitational force. The remnant gas falls into the black hole
producing a bright, month-long flare of radio emission. The ATA?s
unprecedented ability to find transient radio sources will lead to
the discovery of hundreds or thousands of such radio ?flares,?
providing a powerful new way to detect and study massive black
holes. Such flares have distinctive signatures and are so bright
that they can be detected with the ATA to distances as great as
that of any known galaxy.
2. When a massive star runs out of nuclear fuel it collapses under
its own weight, giving birth to a neutron star or a black hole.
The collapse also produces a powerful flare of radiation, a
supernova. Historically, supernovae have been found by their
emission at visible (optical) wavelengths. Over the past few
years, however, it has become clear that they can also be detected
as transient radio sources. The ATA?s study of the transient radio
sky will thus open up a new window into how black holes (and
neutron stars) are formed in the collapse of massive stars.
These examples represent some of the more compelling areas of research
that the ATA can do. But they?re just the tip of the iceberg.
=========================
73 de Alan, (Sysop ZL2AB).
AX25:ZL2VAL@ZL2AB.#46.NZL.OC
IP :zl2val@qsl.net
APRS:!3903.34S/17406.45E]
Message timed: 22:36 on 2004-May-14 (NZT)
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Points to ponder
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Rural wisdom
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Don't sell your mule to buy a plow.
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