JWST & Hubble Deliver Groundbreaking Discoveries Across the Cosmos

A series of recent studies using data from the NASA/ESA/CSA James Webb Space Telescope (JWST) and the NASA/ESA Hubble Space Telescope have yielded findings on star cluster emergence, the reclassification of a stellar system, galaxy formation in the early universe, and the drivers of cosmic reionization.

Star Cluster Emergence in Nearby Galaxies

Observations and Methodology

Astronomers using the JWST and Hubble studied nearly 9,000 young star clusters in four nearby galaxies: Messier 51, Messier 83, NGC 4449, and NGC 628. This research was conducted as part of the FEAST observing programme and published in Nature Astronomy.

The team identified clusters at different evolutionary stages, using Webb to observe those still emerging from gas clouds and Hubble to observe partially cleared and fully unobstructed clusters. Mass and age were estimated from light spectra.

Key Findings

• More massive star clusters cleared away their natal gas clouds faster than less massive ones.
• Massive clusters fully emerged after approximately 5 million years.
• Less massive clusters took 7 to 8 million years to emerge.

Implications and Explanations

One explanation is that massive clusters contain more massive stars, which produce stronger ultraviolet radiation and stellar winds, enabling faster disruption of the surrounding cloud. The timing of cluster emergence affects how young stars heat and ionize gas in their host galaxies.

Researchers noted that protoplanetary disks near massive clusters may be exposed to harsher radiation earlier, potentially affecting planet formation.

The results provide observational constraints for simulations of star formation and stellar feedback.

Reclassification of Terzan 5 as a Bulge Fossil Fragment

Observations and Methodology

Researchers using the JWST and Hubble have determined that the stellar system Terzan 5 is not a globular cluster but a "bulge fossil fragment" containing four distinct stellar populations. Terzan 5 is located in the Milky Way's central bulge. The findings were presented at the 248th meeting of the American Astronomical Society and published in Astronomy & Astrophysics.

Webb's near-infrared observations were combined with Hubble's archival data to measure star colors, brightnesses, and proper motions. Proper motion measurements from Hubble over 12 years allowed the team to separate Terzan 5 stars from foreground Milky Way stars. Spectroscopic data from the Keck Observatory and the Very Large Telescope (VLT) confirmed distinct chemical compositions.

Key Findings

• The four stellar populations formed approximately 12.5, 4.7, 3.8, and 2.5 billion years ago.
• The system retained supernova ejecta, enabling multiple generations of star formation.
• Terzan 5 is one of two known bulge fossil fragments, the other being Liller 1.

Significance

Researchers stated that Terzan 5 is a remnant of a more massive system that formed early in the Milky Way's history and never fully mixed with the bulge.

The findings are considered to provide a local analog for galaxy bulge formation processes in the early universe, where gas disks are thought to have fragmented into clumps that merged to form bulges.

The research team plans to examine 40-50 additional globular clusters in the bulge to identify similar objects.

Confirmation of Distant Galaxy MoM-z14

Observations and Methodology

JWST has confirmed the existence of galaxy MoM-z14 as it appeared 280 million years after the Big Bang. The confirmation used Webb's Near-Infrared Spectrograph (NIRSpec) instrument. MoM-z14 has a cosmological redshift of 14.44, indicating its light has traveled for approximately 13.5 billion years. The findings were published in the Open Journal of Astrophysics.

Key Findings

• MoM-z14 is part of a group of galaxies in the early universe observed to be approximately 100 times brighter than predicted by theoretical studies before Webb's launch.
• The galaxy shows high levels of nitrogen, a feature also observed in a small percentage of ancient stars within the Milky Way galaxy.
• MoM-z14 shows indications of clearing the thick, primordial hydrogen fog in its vicinity, a process known as reionization.

Context and Implications

Prior to Webb, the Hubble Space Telescope had identified GN-z11, a bright galaxy observed 400 million years after the Big Bang, which Webb later confirmed.

Rohan Naidu of MIT's Kavli Institute for Astrophysics and Space Research, lead author of the paper on MoM-z14, stated that observations are "nothing like what we predicted."

One hypothesis for the nitrogen enrichment suggests that the dense environment of the early universe facilitated the formation of supermassive stars, capable of producing higher levels of nitrogen than stars in the local universe. NASA's upcoming Nancy Grace Roman Space Telescope is expected to expand the sample of these bright, compact, and chemically enriched early galaxies.

Identification of Supernova Progenitor

Observations and Methodology

On June 29, 2025, the All-Sky Automated Survey for Supernovae detected supernova 2025pht, originating from a star that exploded 40 million years ago in a nearby galaxy. A team used archival data from JWST to identify the progenitor star.

This marks the first published detection of a supernova progenitor by Webb.

Images of galaxy NGC 1637 revealed a single red supergiant star at the exact location of the supernova. The findings were published in the Astrophysical Journal Letters.

Key Findings

• By aligning Hubble and Webb images of NGC 1637, the team identified the progenitor star in Webb's MIRI and NIRCam images taken in 2024.
• The star appeared notably red, indicating it was enshrouded by dust that absorbed shorter, bluer light wavelengths.
• The dust composition was determined to be carbon-rich rather than the expected silicate-rich.

Significance

The significant dust excess provides a potential explanation for the "missing red supergiants" mystery. The hypothesis suggests that the most massive aging stars are also the dustiest, and if surrounded by substantial dust, their light could be dimmed to the point of being undetectable. The team intends to search for similar red supergiants that may explode in the future.

Dwarf Galaxies as Drivers of Cosmic Reionization

Observations and Methodology

A study utilizing data from Hubble and JWST suggests that small dwarf galaxies were the primary source of photons responsible for clearing the "fog" of neutral hydrogen in the early Universe, a process known as cosmic reionization. The research was published in Nature in February 2024.

An international team led by astrophysicist Hakim Atek of the Institut d'Astrophysique de Paris analyzed JWST data from the galaxy cluster Abell 2744, supported by data from Hubble. Abell 2744 acts as a cosmic lens, magnifying distant light and enabling the observation of tiny dwarf galaxies near the cosmic dawn. Detailed spectra obtained by JWST were used to study these galaxies.

Key Findings

• Dwarf galaxies are the most abundant galaxy type in the early Universe and are brighter than previously expected.
• The team's research indicates that dwarf galaxies outnumber larger galaxies by a ratio of 100 to 1.
• The collective output of ionizing radiation from dwarf galaxies is four times greater than what was typically assumed for larger galaxies.

Context and Implications

Understanding the specific sources responsible for reionization has been challenging due to the vast distances involved. Previous theories often proposed powerful sources such as massive black holes or large, star-forming galaxies as the main contributors.

The researchers intend to study additional cosmic lens regions to obtain a broader sample of early galactic populations.