X-ray astronomy
Branch of physics devoted to the observation of X-rays reaching us from the depths of space. Such radiation is typically produced as the thermal radiation of matter at extremely high temperatures. An important example are the hot gases in the accretion disc ...
world-line
The path of a pointlike object in four-dimensional spacetime is a line called the object's world-line. To every moment in time corresponds one point of that world-line giving the position of the object in space at that particular ...
Wilkinson Microwave Anisotropy Probe
NASA satellite telescope dedicated to observations of the cosmic background radiation. WMAP website ...
Wien’s law
One of the laws governing the properties of the simplest form of thermal radiation – that emitted by a blackbody: the product of such a body's temperature (measured in Kelvin) and the wavelength at which it emits maximal amounts of energy is a universal ...
Why now? puzzle
From astronomical observations, it follows that the density associated with dark energy in our universe has the same order of magnitude as the density of the matter content of the universe. That is remarkable - in the past, the matter density will have been ...
White dwarf
When stars with up to ten solar masses have exhausted the fuel of light atomic nuclei they need to sustain nuclear fusion reactions, they collaps to form a White Dwarf: a comparatively small ball of gas, prevented from further collapse by a quantum mechanical ...
Weyl singularity
A type of spacetime singularity (i.e. a boundary of spacetime) that is associated with infinitely strong tidal forces. More information about the different types of singularities can be found in the spotlight text Spacetime ...
weightlessness
From everyday life, we're used to the Earth's gravity pulling every body down to the ground, and the strength of that force is called its weight. If no such force is present, then bodies placed at a certain location in space simply stay where they are, even ...
