Astrophysics
Glossary
Vocabulary
Definition
Distance unit frequently used in astronomy, defined as the distance traveled by
Light-year
light in a vacuum in one year. 1 light-year is worth approximately 10,000 billion
kilometers (exactly 9,461 billion)
Group of antiparticles forming the "reverse" of matter, the reversal commonly
Antimatter
being at the electric charge: the particles composing the antimatter have
electric charges opposite those of the particles playing the same role in the
matter.
Asymptotic
Blazar (AGN)
Is said of a tendency to get closer and closer to a certain limit without ever
attaining it.
Active galactic nucleus detected by gas blasts who, more or less directed
towards Earth, make it change its luminosity very rapidly.
In string theory, physical-mathematical object of dimensionality going from 0
Brane
to 9, possessing an energy under the form of tension. The usual space in which
we live would be of dimension 3.
Function of several variables that associate a single number (said scalar) to
Scalar field
every point of space. Scalar fields are used in physic to represent spatial
variations of scalar measures like temperature, pressure, etc.
Coalescence
Accretion disk
Kinetic energy
Entropy
Ergosphere
Phenomenon in which two bodies initially separated merge into a single one.
Astrophysical structure formed by matter (gaseous, solid, etc.) in orbit around
a central celestial object (star, black hole, etc.).
Stored energy in a body in motion.
Thermodynamical quantity that measures the degree of disorder inside a
system or, which is the same, the quantity of information that is hidden in it.
Region included between the event horizon of a black hole in rotation and its
static limit, also known as its stationary limit.
Neutron star
Very dense residue that comes from the collapsing of a massive star, sort of
giant atomic nucleus made of neutrons. Sometimes observable under the form
of a pulsar.
Quark star
Hypothetical type of very dense stars made of deconfined quarks, that would
represent an intermediate stage between neutron stars and stellar black holes.
To the difference of Euclidean geometry defined by five postulates placed by
Euclid, a non-euclidean geometry does not satisfy the fifth postulate whereby,
by an exterior point to a straight line, it always passes a parallel to that straight
Non-euclidean
geometry
line and only one. This implies that a non-euclidean geometry possesses a nonzero curvature. In non-euclidean geometries of positive curvature (of spherical
type), there does not exist any parallel, whereas, in geometries of negative
curvature (of hyperbolic type), there is an infinity of it. The description of noneuclidean geometries in the XIXth century revolutionized mathematics and
allowed in particular the formulation of the general relativity theory, which
describes gravity as an effect of curvature of a non-euclidean geometry.
Surface gravity
Gravitational acceleration at the surface of a celestial body.
Hypothetic phase of the very young universe, during which space would have
Inflation
known an expansion phase very violent that would have allowed it to grow of a
considerable factor.
In astronomy, measure instrument comprised of several elements disposed of
in a grid, enables one to obtain thin pieces of information on the structure of
Interferometer
stars observed from interference fringes. An optical interferometer is made of
several optical telescopes, a radio interferometer is comprised of several
antennas and a gravitational interferometer is made up of several beams.
Gravitational
lens
Critical limit
When a massive celestial body – star, black hole, galaxy clusters – is located
between a far luminous source and our telescopes, it makes a phenomenon of
"gravitational lens" by deviating and amplifying the light rays of the
background.
Maximal value that the angular momentum of a black hole in rotation cannot
exceed.
Binary star containing a compact object such as a neutron star or a black hole,
Microquasar
around which the accretion disk produces gaz blasts whose speed approaches
that of light itself.
Also called kinetic moment, measure describing the quantity of rotation of a
Angular
momentum
system in relation to an axe. Dependent on the size of the system, its mass, and
its angular speed, this measure is conserved throughout the evolution of the
isolated system.