Astronomers discover helium-burning white dwarf

A white dwarf star can explode as a supernova when its mass exceeds the limit of about 1.4 solar masses. A team led by the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching and involving the University of ...

Hubble captures cosmic fireworks in ultraviolet

Hubble offers a special view of the double star system Eta Carinae's expanding gases glowing in red, white, and blue. This is the highest resolution image of Eta Carinae taken by the NASA/ESA Hubble Space Telescope.

Arp 299: Galactic Goulash

What would happen if you took two galaxies and mixed them together over millions of years? A new image including data from NASA's Chandra X-ray Observatory reveals the cosmic culinary outcome.

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Double star

In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope. This can happen either because the pair forms a binary system of stars in mutual orbit, gravitationally bound to each other, or because it is an optical double, a chance alignment of two stars in the sky that lie at different distances. Binary stars are important to stellar astronomers as knowledge of their motions allows direct calculation of stellar mass and other stellar parameters.

Since the beginning of the 1780s, both professional and amateur double star observers have telescopically measured the distances and angles between double stars to determine the relative motions of the pairs. If the relative motion of a pair determines a curved arc of an orbit, or if the relative motion is small compared to the common proper motion of both stars, it may be concluded that the pair is in mutual orbit as a binary star. Otherwise, the pair is optical. Multiple stars are also studied in this way, although the dynamics of multiple stellar systems are more complex than those of binary stars.

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