Number 761, January 11, 2006
by Phil Schewe and Ben Stein
Best Direct Test of E=mc2
Albert Einstein's formulation of how
matter and energy are equivalent is an important enunciation of the
principle of conserved energy. As far as we know, it is at work at
the moment an atom bomb explodes, when the fissioning of uranium is
exploited for making commercial electricity, or when an electron and
positron annihilate inside a PET scanner. A new
experiment -- conducted by scientists from MIT, Université Laval in Quebec City, Canada,
Florida State University, Oxford University, the National Institute of Standards and
Technology, and the Institut Laue-Langevin in Grenoble, France -- keeps
careful account of both matter mass and electromagnetic energy for a
process in which ions of sulphur and silicon absorb neutrons,
transforming them into new isotopes as they emit gamma rays. In
this transaction Einstein's equation is shown experimentally to be
true at a level of 0.00004 percent, a factor of 55 better than the previous
best test.
Extrasolar planets in binary star systems
were, at first, unexpected,
since it was thought that the presence of a second or even third
star would disrupt the formation of a planet in the first place.
But then why have 30 such exoplanets been found in double and triple
star groupings? Moreover, some of the planets detected reside in
systems where the companion stars are not far away but actually
rather close in -- tens of astronomical units (one AU equals the
Earth-Sun distance) or less.
At this week's meeting of the American
Astronomical Society (AAS) in Washington, D.C., Alan Boss argued that
the presence of a second star, far from disrupting the formation of
planets around the first star from diffuse matter, can actually
enhance the enterprise. Boss, an astronomer at the Carnegie
Institution of Washington, said that the cross-gravitational forces operating in a
multiple-star system can in some cases, through the process of shock
heating, trigger a faster development of dense spiral arms in which
gas and dust clumping can lead to planets.
Since an estimated two-thirds of all stars in
the Milky Way reside in complex groupings,
Boss asserted that a theory allowing for matter agglomeration in
such places would greatly increase the number of suitable targets
for exoplanet hunters.
Extended Red Emission, or ERE, a mysterious astronomical effect in
which regions of diffuse red light are observed in planetary nebulae
and in the galactic halo, comes from nanodiamonds in space. So say
Huan-Cheng Chang and his colleagues at the Academia Sinica in
Taiwan. At this week's meeting of the
American Astronomical Society in Washington, D.C.,
they reported the results of a recent
experiment. As they suspected that ERE was analogous to the
operation of a fluorescent lamp---where ultraviolet light is
converted into visible light when it strikes a coating inside the
lamp tube.
In the experiment, nanometer-sized diamonds, first
filled with defects by hitting the diamonds with a powerful proton
beam, then heated to a temperature of 800 degrees Celsius to create conditions
roughly matching those of space. When yellow and blue light was
shone on the nanodiamonds, ERE-type luminescence resulted. The
diamonds presumably would have been made in the vicinity of
carbon-rich stellar zones. One example of such emission, in the
proto-planetary nebula HD 44179, also called "The Red Rectangle," can
be seen here. Further
discussion of the Red Rectangle was provided by Boston University
astronomer Kenneth Brecher
(see the Project LITE
Web page).
Shock-Produced Coherent Light
Physicists at MIT and Livermore
National Lab have discovered a new source of coherent radiation
distinct from traditional lasers and free-electron lasers; they
propose to build a device in which coherent photons are produced by
sending shock waves through a crystal. The result would be coherent
light resembling the radiation issuing from a laser; but the
mechanism of light production would not be stimulated emission, as
it is in a laser, but rather the concerted motion of row after row
of atoms in the target crystal.
The passing shock front, set in
motion by a projectile or laser blast, successively excites a huge
density wave in the crystal; the atoms, returning to their original
places in the matrix, emit light coherently, mostly in the Terahertz
wavelength band. Although sources of coherent light in this part of
the electromagnetic spectrum have developed in recent years, it is
still a difficult task.
The next step will be to carry out an
experimental test of the shock-wave light production. This work
will be performed at two national labs -- Livermore and Los Alamos.
According to Evan Reed (who moved from MIT to Livermore,
reed23@llnl.gov) the first likely application of coherent radiation
will be as a diagnostic for understanding shock waves. The
radiation should provide information about shock speed and the
degree of crystallinity.
Reed et al.,
Physical Review Letters, 13 January 2006
Enlarge text
Shrink text
Print
Digg this
Del.icio.us
Furl