Ancient Brightness of Theta Eridani Explained by Binary Interaction
A new study explains why Theta Eridani appeared among the sky’s brightest stars in ancient times: it was in a millennial transient phase where its primary star in a tight inner binary (Theta Aa+Ab) transferred mass during a long-lived common-envelope stage, releasing orbital energy and boosting brightness from about V=0.2 to V=2.9 for roughly 1,000–2,000 years. Now the system has settled into a less eccentric configuration. This suggests such transient brightening could be a common, short-lived phase in close binaries.