Heavy metal

Look: Ruins of an ancient star cluster reveal secrets of the early Milky Way

It’s been part of our galaxy since the dawn of time.

Gabriel Pérez Díaz, SMM (IAC)

While the bulk of the Milky Way spins in an unmistakable spiral, wispy trails of stars find their own orbit around the galaxy’s center.

Known as star streams, these ribbons of light are remnants of the early galaxy.

Billions of years ago, they were organized in globular clusters that held some of the first materials that formed the Milky Way.

NASA/JPL-Caltech/R. Hurt (SSC/Caltech)

International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva/Spaceengine

On January 5, a team of international researchers announced the discovery of a new star stream: C-19.

Its orbit takes it to the far edges of the Milky Way — about 90,000 light years from its center. For comparison, the Earth is about 25,000 light years from the galactic center.

International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva/Spaceengine

Most star streams on record contain low amounts of metals — but C-19 has way less than average.

Gabriel Pérez Díaz, SMM (IAC)


Researchers thought that globular clusters couldn’t have less than 0.2 percent metallicity.

But C-19 has less than 0.05 percent.


“It was not known if globular clusters with so few heavy elements exist — some theories even hypothesized they couldn’t form at all.

Here’s the difference in C-19’s metal concentration compared to other objects in the Milky Way.

N. Martin & Observatoire Astronomique de Strasbourg; Canada-France-Hawaii Telescope / Coelum; ESA/Gaia/DPAC


Metals — in astronomical terms, elements heavier than helium — were essential for forming stars, planets, and other bodies within the early galaxy.

Gabriel Pérez Díaz, SMM (IAC)

Finding star streams with such low concentrations of metals opens the question of how much material was actually needed to create the Milky Way as we know it.

In 2020, a separate team of researchers identified another metal-poor star stream circling our neighboring Andromeda galaxy.

David (Deddy) Dayag via Wikimedia Commons


Having those curious remnants from the primordial days gives researchers a window into understanding the formation of both galaxies — and the universe.