Mark Vogelsberger

Around our Galaxy, like an invisible crown, stretches a tenuous cloud of gas heated to millions of degrees. It is called the galactic halo. Seeing this glow directly is difficult: it emits soft X-rays that are absorbed by Earth's atmosphere.

A field sown with seeds. Some seeds are large and sprout at the slightest rain; others are finicky, requiring special soil and rare conditions. Which seeds fall into the ground determines what kind of forest will grow years later. Astrophysicists think about the birth of black holes in the early universe in much the same way.

Imagine an ancient manuscript, where a new story is written over an old text. Over time, the upper layer wears thin, and lines of the past show through. That’s exactly how globular clusters, the oldest stellar systems in the Universe, are structured, like a palimpsest.