Stars shine light, which is reflected by planets and other objects in space. This is why planets that do not generally produce light are visible to us. But do stars reflect light as well? This subject is surprisingly not very well researched, but now scientists from the University of New South Wales studied a system of binary stars to figure it out.
UNSW astronomers focused on a bright star called Spica (Alpha Virginis). It is actually a system of two stars, orbiting each other with a period of only four days. They wanted to see if they reflect the light from one another so they checked the polarization of light. Star light is usually unpolarised. However, if it would get reflected by another closely orbiting star, it would get polarised, which is exactly what astronomers have found. Polarization that they observed was in line with predictions they did before – stars do reflect light, although, not very well. Scientists estimate that Sun reflects less that 0.1 % of the light falling on it. Spica is a bit brighter and reflects a bit more, but stars are generally poor reflectors of light.
Astronomers say that this newly discovered phenomenon actually has practical implications in terms of research. Scientists say that ability to detect polarization of binary systems will allow to measure different properties of these twin stars. Furthermore, some binary stars are difficult to detect because of their orientation in relation to Earth. Polarization of light could allow scientists to identify these systems and distinguish them from single stars. This method would only apply to binary stars, because single stars don’t have a nearby source of light that they could reflect.
Scientists developed very sensitive astronomical polarimeters that allow observation of stellar reflected light. Interestingly, for this particular study they used a rather small 35 cm telescope, which allowed detecting polarization of light of Spica. Now scientists will test their technique on other binary stars, hoping to see similar results. Professor Jeremy Bailey, one of the authors of the study, said: “We expect it to work even better for hotter stars, and it could be used to find binary systems that are not detectable by other methods, and to study binary star orbits and properties”.
Sources of light can also be reflectors of light – it all depends on composition and materials. But stars are not great reflectors, which means that advanced equipment is needed to detect polarization. It is quite fascinating that we can already accomplish that.