An international team of astronomers has detected only the second and third instances of a rare star system consisting of two central stars orbiting each other, surrounded by a remarkable disk of gas and dust.
Ph.D. “If there was a planet in one of these systems, it would be like the planet Tatooine in Star Wars,” says Michael Poon. David A. Dunlap of the Faculty of Arts and Sciences is a student in the Department of Astronomy and Astrophysics and one of two University of Toronto researchers who participated in the discovery.
“You’d see two suns orbiting each other in the sky. Also, there is a disk around the stars. Imagine Saturn’s rings but much, much larger – with the stars in the middle.”
Such disks are called protoplanetary disks because they eventually form families of planets like our solar system. Newly discovered systems are rare because their disks are at an angle to the orbits of their central star.
“The discovery of objects like this is important to our understanding of planet formation,” says J.J., A postdoctoral fellow at the faculty’s Canadian Institute for Theoretical Astrophysics (CITA), Dr. “Planets are born from them, so the presence of disks around binary stars suggests that we are likely to find more planets orbiting binary.
“They will also help us understand whether life exists on a planet orbiting a binary star at a certain angle, because of how this orientation affects temperature and other conditions.”
The discovery of the new objects, Bernhard-1 and Bernhard-2, is described in a paper published July 4 in The Astrophysical Journal Letters.
The lead author, Wei Zhu of Tsinghua University in Beijing, was formerly a postdoctoral fellow at the Canadian Institute for Theoretical Astrophysics (CITA) of the Faculty of Arts and Sciences. Zanazzi and Poon are co-authors of U of T.
Bernhard-1 and Bernhard-2 are so distant that we cannot see the two central stars separately (such star pairs are known as binary stars). Instead, we only see a single point of light and measure the combined luminosity of the pair.
The researchers identified the new objects by analyzing the complex and distinctive changes in brightness caused by their unusual geometry. A graph of these variations over time is called the light curve, and the delicate curves of the new systems match those of the first system ever discovered – an object called Kearns Herbst 15D (KH 15D).
The light curves of Bernhard-1 and Bernhard-2 dive into some of their peak brightness; the first is 112 days every 192 days; the last 20 days every 62 days. These inclinations signify that one of the stars in each binary is moving behind the disk as seen from Earth. The system’s brightness returns to normal when the star reappears.
Also, when the co-authors compared the latest observations with archival data dating back decades, they found that the brightness of both objects varied over much more extended periods. Previous analysis of KH 15D by Poon, Zhu, and Zanazzi, and work by other researchers, concluded that this long-term pattern reveals that the disk and stars are angled toward each other.