In
stellar astronomy, the Algol paradox is a
paradox
A paradox is a logically self-contradictory statement or a statement that runs contrary to one's expectation. It is a statement that, despite apparently valid reasoning from true premises, leads to a seemingly self-contradictory or a logically u ...
ical situation when elements of a
binary star seem to evolve in discord with the established theories of
stellar evolution.
A fundamental feature of these theories is that the rate of
evolution of stars depends on their mass: The greater the mass, the faster this evolution, and the more quickly it leaves the
main sequence, entering either a
subgiant
A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...
or
giant
In folklore, giants (from Ancient Greek: ''gigas'', cognate giga-) are beings of human-like appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''giant'' is first attested in 1297 fr ...
phase.
In the case of
Algol
ALGOL (; short for "Algorithmic Language") is a family of imperative computer programming languages originally developed in 1958. ALGOL heavily influenced many other languages and was the standard method for algorithm description used by the ...
and other binary stars, something completely different is observed: The less massive star is already a subgiant, while the star with much greater mass is still on the main sequence. Since the partner stars of the binary are thought to have formed at approximately the same time and so should have similar ages, this appears paradoxical. The more massive star, rather than the less massive one, should have left the main sequence.
The paradox is resolved by the fact that in many binary stars, there can be a flow of material between the two, disturbing the normal process of stellar evolution. As the flow progresses, their evolutionary stage advances, even as the relative masses change. Eventually, the originally more massive star reaches the next stage in its evolution despite having lost much of its mass to its companion.
See also
*
Algol variable
Algol variables or Algol-type binaries are a class of eclipsing binary stars that are similar to the prototype member of this class, β Persei (Beta Persei, Algol). An Algol binary is a system where both stars are near-spherical such that ...
References
Paradoxes
Stellar astronomy
{{astronomy-stub