Most distant star found to date may not be a lone star at all

The record holder for the most distant star known to date, nicknamed Earendel, is 12.9 billion light-years away. It’s light left the source when the Universe was less than a billion years old.

However, new data from the James Webb Space Telescope (JWST) suggest that Earendel could actually be a compact group of stars bound together by gravity.

If that reclassification holds, it would reshape how astronomers use rare cosmic alignments to probe the young universe. It would also expand what we can learn about how today’s ancient star clusters first came together.

Why Earendel fooled us

Lead author Massimo Pascale of the University of California, Berkeley, and collaborators, revisited Earendel because the original Hubble detection left room for more than one interpretation.

A recent study pinned the source at redshift 6.2, or about 900 million years after the Big Bang, but a single unresolved point in a highly magnified arc can hide complexity. 

Earendel sits behind a foreground galaxy cluster that acts as a natural telescope through gravitational lensing, the bending and amplification of light by mass.

Subsequent JWST imaging pushed the lower limit on the magnification above 4,000, as reported in a study, which makes an intrinsically tiny source look bright and compact.

With JWST spectroscopy, Pascale’s team also measured a precise redshift for the host, z = 5.926, which set the scene for physically motivated modeling.

Their study explores whether the observed continuum can be explained by a simple stellar population rather than a single hot star.

What JWST added

JWST’s NIRSpec prism provides a smooth spectrum across near infrared wavelengths, which lets astronomers fit how brightness changes with color.

When the team compared Earendel’s spectrum with models of compact clusters that differ in age and chemical content, they found strong consistency with a cluster solution.

“What’s reassuring about this work is that if Earendel really is a star cluster, it isn’t unexpected!” said Pascale. 

“At the spectral resolution of the NIRSpec instrument, the spectrum of a lensed star and a star cluster can be very similar,” said Brian Welch, a postdoctoral researcher at the University of Maryland and NASA’s Goddard Space Flight Center. Not everyone is ready to close the case, and that caution matters. 

Lone stars differ from star clusters

One line of evidence comes from microlensing, a temporary brightening that happens when a smaller mass drifts across the line of sight and briefly focuses the light from the background source.

A compact star should fluctuate more sharply than a larger cluster, so time series monitoring can reveal which interpretation fits the data. 

JWST can also test for subtle spectral signatures that would favor a dominant massive star. If those features are absent, and the light instead aligns with a mix of stars with low metallicity, the cluster hypothesis grows stronger.

Early clusters and star formation

If Earendel is a compact cluster, it may be a direct ancestor of the dense globular cluster populations seen in nearby galaxies today.

The modeling points to low heavy element content and intermediate ages, which is the kind of fingerprint expected for early cluster formation. 

That scenario would give researchers a rare laboratory for star formation under the harsh conditions of cosmic dawn.

It would show that clusters were already assembling packed stellar systems when the universe was young, and that some survived to the present.

There is also a practical payoff for future surveys that chase extreme magnification. Knowing when a bright, unresolved spot is a cluster rather than a single star helps teams plan follow ups that ask the right questions.

Earendel and cosmic alignments

Rare alignments like the one that revealed Earendel are more than lucky accidents. They allow astronomers to study extremely faint and distant objects at levels of detail that would otherwise be impossible with today’s instruments.

Without gravitational lensing, a source this far away would be invisible even to JWST.

Because these alignments are scarce, each one provides unique insights into the universe’s first billion years.

They can reveal galaxies, clusters, and individual stars that serve as anchors for testing models of early structure formation and stellar evolution.

What to watch next

Astronomers will keep an eye on Earendel’s brightness to probe for microlensing, a telltale flicker that is more pronounced for small sources.

If the light curve stays steadier than expected for a star, that will further support the cluster view.

Additional spectra with higher resolution could isolate faint absorption features that are easier to interpret in a cluster context.

They could also refine the contribution from any cooler companions if a star still plays a role.

Either way, the path forward is clear. Better time coverage, sharper spectra, and more lens modeling will push Earendel from a nickname to a well understood object in the early universe.

The study is published in The Astrophysical Journal Letters.

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