Universe Today
Binary star
Two stars orbiting each other, which is at least as common as one on its own.
Roughly half of all star systems contain more than one star, and the fraction rises with mass. Binaries are scientifically invaluable because orbits give masses directly — almost every stellar mass we know is ultimately traceable to one. They also make things happen: a star can strip material from its companion, producing novae, X-ray sources and Type Ia supernovae. Systems that eclipse each other from our line of sight give radii as well, which makes them the calibration standards of stellar astronomy. How close they are decides everything. Wide pairs live out their lives independently and are only useful as a scale; close ones exchange material, and if the receiving star is a white dwarf the transfer eventually detonates it. That is where Type Ia supernovae come from, which is where the distance ladder comes from, which is how the acceleration of the universe was found.
Where it has come up lately
Phys.org
Phys.org
A Pair of White Dwarfs Locked in a Six-Minute Orbit Might One Day Be Observed By Gravitational Waves
Universe Today
Astronomy Magazine
Astronomy Magazine
Related terms
Magnetar
A neutron star with a magnetic field a thousand trillion times Earth's.
Supernova (Type Ia and Type II)
Two unrelated ways for a star to explode, useful for two entirely different reasons.
The main sequence
The long, stable middle age a star spends fusing hydrogen in its core.
Hertzsprung–Russell diagram
The single plot that organises everything about stars.
Questions
What is Binary star?
Two stars orbiting each other, which is at least as common as one on its own.
Why does it matter?
Wide pairs live out their lives independently and are only useful as a scale; close ones exchange material, and if the receiving star is a white dwarf the transfer eventually detonates it. That is where Type Ia supernovae come from, which is where the distance ladder comes from, which is how the acceleration of the universe was found.