stellar astronomy Astronomy is a natural science that studies astronomical object, celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall chronology of the U ...

, 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 or apparently true premises, leads to a seemingly self-contradictor ...

ical situation when elements of a

binary star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

seem to evolve in discord with the established theories of

stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is consi ...

. 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 In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

, 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 ...

giant In folklore, giants (from Ancient Greek: ''wiktionary:gigas, gigas'', cognate wiktionary:giga-, giga-) are beings of humanoid appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''gia ...

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.

References

Paradoxes Stellar astronomy {{stellar-astronomy-stub

See also

References