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starship-design: update.468 (fwd)

Hi all,
	Interesting stuff.  Enjoy.
Nels Lindberg

---------- Forwarded message ----------
Date: Fri, 28 Jan 2000 16:15:50 -0800 (PST)
From: N. Lindberg <nlindber@u.washington.edu>
To: N. Lindberg <nlindber@u.washington.edu>
Subject: update.468 (fwd)

---------- Forwarded message ----------
Date: Thu, 27 Jan 2000 09:51:13 -0500 (EST)
From: daemon@u.washington.edu
Newsgroups: uwash.physics.grad
Subject: update.468

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 468  January 25, 2000   by Phillip F. Schewe and Ben Stein

OPTICAL BLACK HOLES, objects that attract and trap specific colors of
light, can be made in earthly laboratories, two researchers have shown
theoretically, offering possibilities for lab-based analogs of general
relativity and potentially even quantum gravity phenomena. According to
researchers at the Royal Institute of Technology in Sweden and at the
University of St Andrews in Scotland (Ulf Leonhardt,
leonhardt@quantopt.kth.se, 011-46-8-791-1324), the trick is to create a
vortex of fluid that whirls at velocities comparable to the speed of light
inside the fluid. Such a feat is now possible, with the advent of techniques
for slowing down light to just a few meters per second through such
substances as a Bose-Einstein condensate (Update 415) or a rubidium gas
(Phys. Rev. Focus, 29 June 1999). If  a sufficiently fast-spinning vortex of
these or similar materials could be created, light inside the fluid could lose
maneuverability and become trapped in the vortex.  Since light in an
optical black hole would behave analogously to matter in a real black
hole, these light-trapping whirlpools would permit laboratory study of
Hawking radiation, the hypothetical emissions from evaporating black
holes; this radiation, which consists of particles made near the hole's
boundary,  is next-to-impossible to observe directly since it is obscured by
the cosmic microwave background. In addition, the researchers speculate
that studying quanta of light interacting with the quantum-mechanical
matter waves in BECs could even help establish "a testable prototype
model of quantum gravity." In the meantime, physicists are also pursuing
the idea of creating "acoustical black holes" (dumb holes), regions that
capture and trap sound waves. (Leonhardt and Piwnicki, Physical Review
Letters, 31 January 2000; Physical Review A, December 1999; Select
Articles; also see http://www.st-

connected to the presence of a central massive black hole," asserts
Douglas Richstone of the University of Michigan.  Richstone was at the
recent meeting of the American Astronomical Society in Atlanta to report
the new identification of supermassive black holes at the cores of three
nearby elliptical galaxies, adding to an already substantial association
between galaxies possessing centralized, high-density spheroidal clumps
or bulges of stars and nearby heavy black holes (star concentration
correlating closely with black hole mass).  Richstone pointed to the
growing consensus that these massive black holes are the remnants of
quasars (a notion underscored at the meeting by the report given by
Andrew Wilson of the University of Maryland--of many "dying quasars"
in nearby galaxies, objects whose radio spectra resemble a quieter version
of quasar spectra) and to the historical fact that the age of quasar
formation occurred before the time when most stars were forming in
galaxies (to judge from high redshift observations).  Richstone concluded
that "Radiation and high-energy particles released by the formation and
growth of black holes are the  dominant sources of heat and kinetic energy
for star-forming gas in protogalaxies."

SNOW SCREECHING ON WATER.  With its ability to create muffled
winter landscapes, snow is usually associated with quiet.   When the white
stuff falls on a body of water, one would expect it to be just as silent, since
it doesn't make much of an impact.  But as researchers have discovered, it
unexpectedly creates high-pitched screeching sounds that can sometimes
disrupt underwater sonar experiments.  Investigating these sounds, which
last for roughly a ten-thousandth of a second, Larry Crum of the
University of Washington (206-685-8622) and his colleagues implicate air
bubbles as the source of snowflake noise.  According to their explanation,
the snowflake's presence on a water surface creates capillary action (the
attraction between a liquid and solid surface), causing water to rush
upwards.  The upward flow of water either generates air bubbles on its
own, or unleashes air bubbles in the snowflake as it melts.  The bubbles
oscillate as they reach equilibrium with their environment, creating sound
waves of up to 200 kilohertz--out of the range of human hearing (which
stops at 20 kHz) but potentially audible to dolphins.  Researchers have
been known to shut down sonar surveys of salmon population during
snowfall because of these sounds.  (Select Article, Journal of the
Acoustical Society of America, October 1999; see also New Scientist, 25
December 1999.)