Gang Zhao

15 175 107 stars. Each one got an age. But no number is free of uncertainty: a star's age isn't a nail hammered into the timeline: it's a probability cloud, a fog hiding the true value. For galactic evolution, such a timestamp is priceless: without it, the map of the Milky Way remains flat.

Imagine three witnesses who saw the same event. Two tell the same story, the third tells a different one. Whom do you believe? This is exactly the situation in astronomy when measuring carbon in the star J0815+4729, an ancient object with a record-low iron abundance (carbon is one of the key elements used to infer the properties of the…

In the vast choir of galactic nuclei, some voices ring out louder than the rest. In quasars whose spectral nitrogen lines are anomalously strong, the chemical makeup of the gas in the broad-line region (the gas whipping around the black hole at enormous speeds) long remained a puzzle. Astronomers argued: is all the gas there simply rich in metals, or has nitrogen in particular been added beyond measure?