DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

For instance, in a model higher derivative quantum
gravity, the massive spin-2 ghosts have negative
kinetic energy and they interact with physical
particles such as gravitons. As a result they
lead to the instability of the classical solutions
and, on a quantum level, to the loss of conservation
probably in interaction (loss of unitarity
of the physical S matrix). See higher derivative
theories.
mass-luminosity relation The relation between
luminosity and mass for main sequence
stars. As the mass of a star increases, the pressure
in its core, and hence its temperature, also
increases. Hence, as the mass of a star increases,
it burns hydrogen more rapidly in its
core and is consequently brighter. The massluminosity
relation for main sequence stars is:
L∝M x where x is roughly 3. This relation
only holds when comparing stars lying on the
main-sequence (hydrogen burning stars). A low
mass giant star can be brighter than a higher
mass main sequence star.
mass transfer Mass transfer occurs in binary
star systems when one star overfills its
Roche-lobe and accretes onto its companion.
Binarymasstransferisseparatedintothreecases
depending upon the evolutionary phase of the
mass-losing star (Case A, Case B, Case C). Case
A denotes the mass transfer that occurs during
hydrogen burning. Case B mass transfer occurs
after hydrogen burning, but before helium core
ignition. Case C mass transfer denotes any mass
transfer which occurs after helium core ignition.
If the orbital angular momentum of the system
is conserved during the mass transfer phase, the
mass transfer is denoted “conservative”. The
orbital separation of the binary is uniquely determined:
a
a0
=
M1 M1 0
−2
M2 M2 −2 0
where the subscript 0 denotes the initial conditions.
Note that if the mass-losing star is less
massive than the accreting star, the orbit widens,
and if it is more massive, the orbit decreases. In
nature, however, orbital angular momentum is
lost from the system either as mass escapes the
© 2001 by CRC Press LLC
,
Maunder Minimum
binary or as mass forms an accretion disk and
spins up the accreting star.
mass wasting Also called mass movement,
mass wasting is the downhill movement of soil
or fractured rock under the influence of gravity.
Common features associated with mass wasting
include landslides (including rockslides, mudflows,
Earthflows, and debris avalanches), rock
falls (also called talus slopes), soil creep (the
very slow (usually imperceptible) downhill flow
of soil under the influence of gravity), and solifluction
(movement of frozen soil).
matter density perturbations Inhomogeneities
in the matter distribution in the universe.
The density fieldδ(x)=(ρ(x)−ρo)/ρo
is usually characterized by its Fourier transform
δ(k). It is often assumed that the Fourier modes
are Gaussian random variables. In this case, the
power spectrumP(k) =< |δ(k)| 2 >, suffices to
characterize all the statistical properties of the
density field. Two theories compete to explain
theoriginofdensityperturbations: (1)theywere
generated during inflation, favored by the data
on cosmic microwave background temperature
anisotropies, or (2) they are the result of distortions
produced by topological defects (cosmic
strings or domain walls) on a homogeneous
background. Inflation generically predicts that
today P(k) ∝k n with n∼ 1 on scales close to
the horizon size.
The exact shape of the power spectrum is one
of the most challenging problems of observational
cosmology. Given an initial density field,
density perturbations can be evolved in time and
the power spectrum at present can be computed.
The final processed spectrum depends on the geometry
of the universe, the baryon fraction, and
the amount and nature of the dark matter. In
the figure on page 308 we plot a compilation of
the power spectrum obtained from the distribution
of galaxies and clusters in different catalogs.
The largest scale sampled by the data is
600h −1 Mpc. The amplitude is different since
clusters and galaxies are biased tracers of the
matter distribution. See biasing parameter.
Maunder Minimum The period from 1645
to 1715 during which the number of sunspots
on the solar disk was severely depressed and,
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