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Globular Cluster

James Webb Spots a Globular Cluster Sparkling with Separate Stars!

The JSWT is part of the Early Release Science program. And Webb’s conducted one of initial scientific observations by gazing at Messier 92 (M92). M92 is a globular cluster in the Milky Way halo, Which is approximately 27,000 light-years away. This occurred on June 20, 2022, and lasted for slightly over an hour. There are 13 ERS programs that assist astronomers in comprehending how to utilize Webb and leverage its scientific capabilities.

Matteo Correnti is from the Italian Space Agency. Alessandro Savino is from the University of California, Berkeley. Roger Cohen is from Rutgers University. Andy Dolphin is from Raytheon Technologies. They were interviewed to gather insights into Webb’s observations of M92. The team is utilizing the data to assist other astronomers. Kristen McQuinn had previously discussed her research on the dwarf galaxy WLM. The dwarf galaxy WLM is also included in this initiative. This conversation happened last November.

What is the purpose of ERS program?

Alessandro Savino:

The emphasis of this program is on studying resolved stellar populations. These are massive collections of stars such as M92 that are located near us, making it possible for Webb to isolate each star within the system. From a scientific perspective, these observations are highly captivating as they offer insights into the physics of stars and galaxies that can be gathered from entities situated much further away. It is through our study of our local cosmic environment that we gain much of our understanding of these distant objects.

Matteo Correnti:

We are also working towards enhancing our understanding of the telescope. This initiative has played a crucial role in refining the calibration process to ensure the highest level of measurement accuracy, which will benefit other astronomers and comparable projects by improving the quality of the data obtained.

Why did you decide to look at M92 in particular?


M92 and other globular clusters hold great significance in comprehending the process of stellar evolution. For many years, they have been serving as a vital standard for comprehending the workings and development of stars. M92, a prime example of a globular cluster, is near us and is well-understood, making it a crucial reference point in studies of stellar systems and their evolution.


M92 holds significant importance due to its status as one of the Milky Way’s oldest globular clusters, potentially even being the oldest. With an estimated age of 12 to 13 billion years, M92 hosts some of the most ancient stars that can be observed and analyzed. These nearby clusters serve as valuable indicators of the early universe, aiding in our understanding of its origins.

Roger Cohen:

One of the reasons why we selected M92 is due to its high density, where numerous stars are tightly packed together. The core of the cluster is thousands of times denser compared to the region surrounding the Sun. Studying M92 will enable us to evaluate the performance of Webb in this specific regime, where we need to measure stars that are in very close proximity to each other.

Characteristics of a globular cluster- studying stars’ evolution!

Andy Dolphin:

A key feature of M92 is that the majority of its stars likely originated from a single period of formation and with similar elemental compositions, yet they exhibit a diverse range of masses. This provides an excellent opportunity to study this specific cohort of stars in depth.


Furthermore, as all the stars are part of the same entity, namely the globular cluster M92, it is evident that they are all at approximately the same distance from us. This fact is quite useful because it implies that any variations in brightness amongst the stars are most likely due to inherent characteristics, rather than just being influenced by their respective distances. Consequently, it simplifies the process of comparing the stars with models to a significant extent.

Hubble Space Telescope Vs Webb!


Webb and Hubble Telescope differ significantly in terms of their wavelength range. Webb is capable of operating at longer wavelengths, where the majority of light emission comes from cool, low-mass stars. This makes Webb particularly applicable for observing such stars. Webb is capable of detecting stars with masses less than 0.1 times that of the Sun, which is intriguing because this is close to the point where stars cease to exist as stars. Beyond this boundary lies brown dwarfs, which are too low-mass to generate hydrogen ignition in their cores.


In comparison to Hubble Webb offers a significant increase in speed. To observe the extremely faint low-mass stars using Hubble,

It needs hundreds of hours of telescope time, whereas, with Webb, it only takes a few hours.


The purpose of these observations was not to test the full capabilities of the telescope, yet it is reassuring to find that we were able to detect dim and tiny stars without exerting excessive effort.

Facts about the low-mass stars!


To begin with, they constitute the largest population of stars in the entire universe. Secondly, they hold significant theoretical interest due to the challenges in observing and characterizing them, particularly those with a mass of less than half that of the Sun, where our comprehension of stellar models remains somewhat uncertain.


By examining the light that low-mass stars emit, we can enhance our ability to determine the age of the globular cluster. This knowledge, in turn, can provide us with a deeper understanding of the formation of various components of the Milky Way, such as the halo where M92 is situated. These insights into cosmic history can have far-reaching implications.

The Chip gap:

chip gap
Image credit: NASA, ESA, CSA, A. Pagan (STScI).

The utilization of Webb’s Near-Infrared Camera (NIRCam) helps in the creation of this image. NIRCam consists of two modules and the “chip gap” separates it. The central area of the cluster is both densely populated and exceptionally luminous, which restricted the applicability of the data gathered from that zone. However, the positioning of these images aligns well with the Hubble data that is already accessible.

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