Scientists prove that binary stars reflect light from each other

UNSW astronomers have shown that binary stars – two stars blocked one around the other – reflect and radiate light, thus revealing new methods of detection.

One of the first things we learn in astronomy is that some objects in the sky (the sun and stars) produce their own light, while others (the moon and the planets) are visible only because they reflect the sunlight.

But do the sun and stars also reflect some of the light that falls on them?

This is a question that scientists from UNSW Sydney and Western Sydney University wanted to discover, which is quite surprising and has been little studied by astronomers.

In their article published in Nature Astronomyresearchers have shown that stars reflect light well and that light could be a useful tool for astronomers.

Stellar reflection is the most significant in a near binary system, where two stars are in orbit around one another. Such binary systems are thought to be common, with most stars in the universe supposed to have binary companions.

Scientists have studied the bright star Spica (Alpha Virginis), which is actually two hot stars that revolve around each other in a period of just four days. They found that starlight is polarized in a way that varies as the stars move on their orbit.

Professor Jeremy Bailey, of the UNSW School of Physics, said that normally, the light of a star is not polarized, which means that it vibrates in several plans. But when the light of a star reflects that of another star, it becomes polarized and the vibrations of light waves now travel in a single plain.

He said that it was a process similar to the way the light is polarized when it is reflected on a glass or water surface, allowing us to reduce glare with the help of glasses polarized sunglasses.

"We were able to determine that the amount of polarization observed was exactly the same as that predicted for a reflected light model," said Professor Bailey.

"Our modeling has shown that stars are actually very poor light reflectors – the Sun, for example, reflects less than 0.1% of the light falling on it.

"However, for warmer stars, such as Spica components, with temperatures between 20,000 and 25,000 degrees Kelvin, the amount of reflection increases to a few percent." The total amount of reflected light from the Spica system remains however very small. "

Professor Bailey explained that the reason this discovery was important was that it would now allow astronomers to measure the properties of stars that they can not easily measure for a single star.

"It provides a way to detect binary systems that could not be detected by other methods – especially face-to-face orbit binaries – and a way to measure masses for a wider range of binaries than any other." 39, it is currently possible, "he said.

"Simple stars do not have a nearby light source (like the binary companion) and so it's impossible to measure the small amount of reflected light."

According to Professor Bailey, the observation of stellar reflected light is made possible by the fact that the light is highly polarized and measurable with the very sensitive astronomical polarimeters that he and his colleagues at UNSW have developed.

"For this work, we used three different telescopes, including the UNSW observatory, located on campus." The small 35 cm telescope here was used to perform most of the observations included in this study. ", did he declare.

Professor Bailey said that he and his colleagues are currently testing their techniques on other binary systems and believed that the polarization technique could open new perspectives for the study of binary stars.

"We expect it to work even better for warmer stars, and it could be used to find binary systems that are undetectable by other methods, and to study the orbits and properties of binary stars," did he declare.