e-Pulsar - Jun

e-Pulsar Jun - Jul 99

Astronomical Feature of the Month
BINARIES

"TMR-1" By John Whatamough

Here’s an image of what is suspected to be the first extra-solar planet to be seen in visible light (see Oct/Nov 98 Pulsar). The giant gas glows red with heat while the dust from the newly formed binaries blocks out all starlight.

TMR-1 Planet's revolve around stars because of gravity. However, stars can revolve around stars as well, where they obey Kepler's Laws of Planetary Motion just like planets do. In fact, 85% of the stars in the Milky Way galaxy are not single stars, like the Sun, but multiple star systems, binaries or triplets.

If two stars orbit each other at large separations, they evolve independently and are called a "wide pair." If the two stars are close enough to transfer matter by tidal forces, then they are called a close or contact pair. Any two stars seen close to one another is a double star, the most famous being Mizar and Alcor in the Big Dipper. Odds are, though, that a double star is probably a foreground and background star pair that only looks near each other. With the invention of the telescope may such pairs were found. Herschel, in 1780, measured the separation and orientations of over 700 double stars and found that only about 50 pairs changed orientation over 2 decades of observation. When two stars are close in separation it is possible for tidal forces to come into play. Since stars are made of gases, gravity can strip material and transfer it from one star to the other. Thus we say the binaries are in contact, even if their surfaces are not touching directly. Lines of potential exist around stars where the gravitational pull from one star exceeds that of another. The line where the forces balance is called the Roche lobe. Binary orbits When the star's radii exceed the Roche lobe, then gases are free to transfer from one star to the other, usually in the form of a tube or stream. In a particularly energetic binary pair, one star could be twisted and drawn out into spinning flattened disk. Wouldn't that make a great picture?....

Source: zebu.uoregon.edu/~js/ast122/lectures/lec11.html

Epsilon

"Epsilon" By Marcus Usherwood
A beautiful image of twin suns shown from an icy world.