gamma-ray burst
Astronomical events visible as extremely strong flashes of gamma rays. Their origin is still unclear; In the context of general relativity they are interesting because they are thought to signal the mergers of neutron stars and/or black holes. Shortly after ...
galaxy
Stars are rarely found alone - usually, they congregate in conglomerates of millions, billions or even more stars called galaxies. A case in point is our sun, part of a galaxy we call the milky way. The life of a young galaxy can be very turbulent. ...
galaxy cluster
Galaxies are not solitary objects - usually, they cluster together. Our own galaxy for instance, the Milky Way, is part of a small cluster called the local group of galaxies. The next-closest large galaxy cluster is the Virgo ...
Friedmann-Lemaître-Robertson-Walker universe
The simplest assumptions one can make about a universe are that it is homogeneous and isotropic. Homogeneity means that the properties of matter and of the geometry of spacetime are the same at every point in space. Isotropy means that all spatial directions ...
frequency
Measure for the rapidity of an oscillation, defined as the inverse of the period of oscillation: A process that, in oscillating, repeats itself after 0.1 seconds has the frequency 1/(0.1 seconds)= 10 Hz. (The unit Hertz, abbreviated as Hz, ...
free
In the context of relativity theory, a particle (object, observer...) that is not acted upon by any force except gravity is said to be free or, a bit more specific, to be in free fall. Free test particles play an important role in understanding the structure ...
