Ancient north star and its fainter companion regularly eclipse each other
NASA's Transiting Exoplanet Survey Satellite (TESS) has revealed that Alpha Draconis or Thuban, a well-studied ancient north star visible to the unaided eye and its fainter companion star regularly eclipse each other. While the binary nature of the system was previously known, the mutual eclipses came as a complete surprise to scientists.
Alpha Draconis is located about 270 light-years away in the northern constellation Draco. Despite its alpha designation, it shines as the eighth-brightest star in the constellation.
Some 4,700 years ago, Thuban appeared as the North Star, closest to the northern pole of Earth's spin axis. It later lost its status to Polaris, a brighter star in the constellation Ursa Minor, because of Earth's axial precession.
The stars in the Thuban system orbit every 51.4 days at an average distance slightly greater than Mercury's distance from the Sun. The primary star is 4.3 times bigger than the Sun and has a surface temperature of around 17,500 degrees Fahrenheit (9,700 C), making it 70% hotter than our Sun. Its companion, which is five times fainter, is most likely half the primary’s size and 40% hotter than the Sun.
A 2004 report hinted at potential brightness changes in Thuban, suggesting the possibility of pulsations in the system's brightest star. To check this, Timothy Bedding, Daniel Hey, and Simon Murphy at the University of Sydney, Australia, and Aarhus University, Denmark, turned to TESS measurement and discovered mutual eclipses whilst ruling out the existence of pulsations over periods less than eight hours.
Now Kochoska and Hey plan to delve deeper into the system to understand it in greater detail. Kochoska plans to conduct ground-based follow-up observations and anticipates more eclipses in future TESS sectors.
Here be dragons!In the constellation of the Dragon – Draco – lies Alpha Draconis, a star visible to the unaided eye and located 270 light-years away. NASA’s TESS discovered that it has mutual eclipses with its fainter companion star. https://t.co/JAOnOG995H pic.twitter.com/8HBblahX3J
— NASA Universe (@NASAUniverse) January 16, 2024