Binary Stars
What is a Binary Star System???
A binary star system consists of two stars which orbit around a common point,
called the center of mass following Kepler’s 3rd law we will compute this
in the lab on Thursday.
The component stars in multiple systems orbit each other, and move around their
center of mass, because of their mutual gravitational interaction,
Five to ten percent of the stars visible to us are visual binary stars.
Careful spectroscopic studies of nearby solar-type stars show that about two
thirds of them have stellar companions.
It is estimated that roughly half of all stars in the sky are indeed members
of binaries.
Binary and multiple stars are common in the universe. Stellar formation results in multiple systems at least as often as in single stars like our Sun, as observations suggest.
Types of Binaries
Visual Binaries: Visual binaries are systems in which the individual stars can be seen through a telescope.
Spectroscopic Binaries: Are systems in which the stars are so close together that they appear as a single star even in a telescope. The binary nature of the system is deduced from the periodic doppler shifts of the wavelengths of lines seen in the spectrum, as the stars move through their orbits around the center of mass.In some instances, the spectrum shows the lines from both stars; this case is called a double-lined spectroscopic binary. In other cases, only one set of lines is seen, the other star being too faint, and we call the system a single -lined spectroscopic binary.
Eclipsing Binaries: Eclipsing binaries are systems in which the orbital plane is oriented exactly edgewise to the plane of the sky so that the one star passes directly in front of the other, blocking out its light during the eclipse. Eclipsing binaries may also be visual or spectroscopic binaries. The variation in the brightness of the star is called its light curve.
X-Ray Binary
A special class of binary stars is the X-ray binaries, so-called because they
emit X-rays. X-ray binaries are made up of a normal star and a collapsed star
(a white dwarf, neutron star, or black hole). These pairs of stars produce X-rays
if the stars are close enough together that material is pulled off the normal
star by the gravity of the dense, collapsed star. The X-rays come from the area
around the collapsed star where the material that is falling toward it is heated
to very high temperatures (over a million degrees!)In an X-ray binary, material
from one star falls towards the other compact star, forming an accretion disk
around it. The compact star may be a white dwarf, a neutron star, or a black
hole. The in-falling material is accelerated and heats up. A "hot spot"
develops where the infalling material colides with the material already in the
accretion disk and X-rays are emitted.