Webb Telescope is trying to confirm a new type of star system present in our galaxy

Astronomers have argued for centuries about how the oldest, tightest star swarms came to be. A new study uses precise computer models to show how this new type of star system might form.

The findings point to a new class of objects that could be hiding near the Milky Way today.

These star systems are called globular clusters (GCs). They pack hundreds of thousands of stars into regions only a few dozen light years wide.

Most show no clear sign of dark matter, and their stars share similar ages and chemical fingerprints, which makes their origin a stubborn puzzle.

Dr. Ethan D. Taylor, a postdoctoral research associate at the University of Surrey, led the work and coordinated a team spanning several institutions.

The group built a detailed virtual universe and watched globular clusters assemble across 13.8 billion years of cosmic history.

What the new simulations show

The team’s EDGE simulations track gas, stars, and gravity at roughly 10 light years of detail, which is fine enough to follow the punch of single supernova explosions. 

“Here we present a suite of cosmological simulations in which both dark-matter-free GCs and dark-matter-rich dwarf galaxies naturally emerge in the Standard Cosmology,” wrote Taylor.

The models show two formation routes for clusters. Some grow steadily near the centers of small galaxies, while others ignite farther out during mergers, then survive because they live in calmer neighborhoods.

A surprise appears between clusters and small galaxies, however. The simulations revealed globular cluster-like dwarfs (GCDs), which are compact systems that resemble clusters but sit in their own dark matter halos.

The researchers concluded that their models point to the existence of this new type of star system, one that bridges the gap between traditional globular clusters and dwarf galaxies.

The EDGE runs also match observed properties such as size, color, and narrow spreads in age and metals for true clusters.

That agreement matters because it suggests the virtual systems behave like real ones rather than artifacts of the code.

Star systems form without dark matter

In the simulations, clusters form from gas that is already enriched by previous stars. A burst of star formation lights up, then winds and one or a few supernovae blow the gas out, shutting growth off quickly.

Because there is no dark matter halo anchoring the gas, the star-making fuel does not return. The result is a tight group with a very small spread in ages and chemical elements.

By contrast, dwarf galaxies keep forming stars for longer periods because their dark matter halos hold onto gas. Their stars show a wider range of ages and a larger spread in elements forged by earlier stars.

Only the most massive clusters born in quieter environments last to the present day. The rest get torn apart by tides or fade as their most massive stars age and die.

Are GCDs a new star system

Globular cluster-like dwarfs (GCDs) form in tiny, dark matter halos early in time, then shut down after a single intense starburst.

Their sizes fall between typical clusters and dwarfs, and their dark matter raises their dynamical mass above cluster values.

They carry modest spreads in age and metal content, larger than clusters but smaller than dwarfs. That middle ground in size, brightness, and internal motions is the telltale signature.

Some GCDs may host metal-free stars, the first generation born from pristine gas with no heavy elements. Finding even a few of these stars would open a window on the earliest phases of star formation.

Why Reticulum II matters

One nearby dwarf galaxy, Reticulum II, orbits the Milky Way at about 100,000 light years. It is faint, compact, and unusually distinct in chemical characteristics.

In 2016, astronomers reported clear evidence that many of Reticulum II’s stars are loaded with heavy elements made by the rapid neutron capture process, or r-process.

That chemical pattern points to a single, powerful event early in the galaxy’s life.

Follow-up deep Hubble Space Telescope photometry shows that most of its stars formed very early, with a short burst near the era when the first galaxies ionized the cosmos.

That timing supports the idea that a rare event seeded the gas before star formation shut down.

If Reticulum II is a GCD rather than a regular cluster or dwarf, it becomes a natural testbed. Its chemistry, age spread, and internal motions can be checked against the simulation predictions.

GCDs, Reticulum II, and new star systems

Confirming GCDs requires sharper measurements of stellar motions and chemical spreads in these tiny star systems.

The James Webb Space Telescope (JWST) can already map star formation histories in nearby dwarf galaxies with enough precision to separate subtle patterns.

Webb can measure very faint stars in crowded regions, extract spectra for chemical tagging, and help pin down internal velocity dispersions. Those data reveal whether a candidate sits in a dark matter halo or not.

Targets like Reticulum II and similar, ultra faint satellites are within reach.

With careful spectroscopy and deep imaging, observers can place each star system on the size, brightness, and mass map that separates clusters, dwarfs, and the proposed middle class.

If even a few objects land in the predicted middle ground, the case for GCDs strengthens. That would give astronomers new levers for testing dark matter models and a new path to hunt the universe’s earliest stars.

The study is published in Nature.

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