Star clusters found in the Cosmic Gems arc by Webb

Massive star clusters found in early universe

Young galaxies in the early universe underwent phases of significant bursts of star formation, generating substantial amounts of ionizing radiation, that is, a type of energy released by atoms that travels in the form of electromagnetic waves (gamma or X-rays) or particles (neutrons, beta or alpha). However, because of their cosmological distances, direct studies of their stellar content have proven challenging.

Using the James Webb Space Telescope, an international team of astronomers have now detected five young massive star clusters in the Cosmic Gems arc (SPT0615-JD1). It’s a strongly-lensed galaxy emitting light when the universe was roughly 460 million years old, looking back across 97% of cosmic time.

The Cosmic Gems arc was initially discovered in Hubble Space Telescope images obtained by the (Reionization Lensing Cluster Survey) RELICS program. It was found when imaging the lensing galaxy cluster SPT-CL J0615-5746.

The lead author of the study is Angela Adamo of Stockholm University and the Oskar Klein Centre in Sweden. Angela said:

These galaxies are thought to be a prime source of the intense radiation that reionized the early universe. What is special about the Cosmic Gems arc is that thanks to gravitational lensing we can actually resolve the galaxy down to parsec scales!

Star clusters: A field of galaxies on the black background of space.
Astronomers used the James Webb Space Telescope to discover gravitationally bound star clusters when the universe was 460 million years old. This is the 1st discovery of star clusters in an infant galaxy less than 500 million years after the Big bang. Image via ESA/ Webb/ NASA/ CSA.

Webb can image distant and young stars

With Webb, the science team can now see where stars formed and how they are distributed. That’s similar to how the Hubble Space Telescope studies local galaxies. Webb’s view provides a unique opportunity to study star formation and the inner workings of infant galaxies at such an unprecedented distance.

Larry Bradley of the Space Telescope Science Institute and PI of the Webb observing program said:

Webb’s incredible sensitivity and angular resolution at near-infrared wavelengths, combined with gravitational lensing provided by the massive foreground galaxy cluster, enabled this discovery. No other telescope could have made this discovery.

According to Adamo:

The surprise and astonishment were incredible when we opened the Webb images for the first time. We saw a little chain of bright dots, mirrored from one side to the other; these cosmic gems are star clusters! Without Webb we would not have known we were looking at star clusters in such a young galaxy!

The Cosmic Gems arc offers clues to early star formation

In our Milky Way we see ancient globular clusters of stars, which are bound by gravity and have survived for billions of years. These are old relics of intense star formation in the early universe. However, it’s not well understood where and when these clusters formed.

The detection of massive young star clusters in the Cosmic Gems arc provides us with an excellent view of the early stages of a process that may go on to form globular clusters. The newly detected clusters in the arc are massive, dense and located in a very small region of their galaxy. And they also contribute the majority of the ultraviolet light coming from their host galaxy. The clusters are significantly denser than nearby star clusters. This discovery will help scientists better understand how infant galaxies formed their stars. Plus, it can help astronomers see where globular clusters formed.

The team notes that this discovery connects a variety of scientific fields. Adamo explained:

These results provide direct evidence that indicates proto-globular clusters formed in faint galaxies during the reionization era, which contributes to our understanding of how these galaxies have succeeded in reionizing the universe. This discovery also places important constraints on the formation of globular clusters and their initial properties. For instance, the high stellar densities found in the clusters provide us with the first indication of the processes taking place in their interiors, giving new insights into the possible formation of very massive stars and black hole seeds, which are both important for galaxy evolution.

Future studies

In the future, the team hopes to build a sample of galaxies for which similar resolutions can be achieved. Eros Vanzella from the INAF Astrophysics and Space Science Observatory of Bologna (OAS) said:

I am confident there are other systems like this waiting to be uncovered in the early universe, enabling us to further our understanding of early galaxies.

In the meantime, the team is preparing for further observations and spectroscopy with Webb.

Bradley added:

We plan to study this galaxy with Webb’s NIRSpec and MIRI instruments in Cycle 3. The NIRSpec observations will allow us to confirm the redshift of the galaxy and to study the ultraviolet emission of the star clusters, which will be used to study their physical properties in more detail. The MIRI observations will allow us to study the properties of ionized gas. The spectroscopic observations will also allow us to spatially map the star formation rate.

Bottom line: The Webb Space Telescope has discovered massive young star clusters in the Cosmic Gems arc. This can give astronomers insight on how galaxies and globular clusters formed.

Source: Bound star clusters observed in a lensed galaxy 460 Myr after the Big Bang


June 26, 2024

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