Unlocking the History of Globular Cluster Messier 5

An image of the globular cluster Messier 5
A brand new examine means that globular cluster Messier 5, in any other case often called NGC 5904, is extra difficult than it appears.
ESA / Hubble / NASA

New Understanding of Old Objects

Early theories recommended that each one the stars in a globular cluster kind at the similar time from the similar materials, leading to a single stellar inhabitants that’s chemically equivalent. However, more moderen work has discovered that some stars in globular clusters present indicators of chemical evolution, hinting that they shaped from gas enriched by earlier generations of stars.

In order to study extra, we have to measure the chemical abundances of a whole bunch of cluster stars. Performing this chemical tagging is difficult — detecting delicate enhancements in elemental abundances requires exact measurements, and the typical strategies have critical drawbacks. Spectroscopy is a robust software for figuring out chemical abundances, however spectra of stars so densely packed are sometimes contaminated. Broadband photometry, on the different hand, doesn’t undergo from contamination however isn’t delicate sufficient.

An image of the globular cluster Messier 5
It will be difficult to review the stars in the densely packed facilities of globular clusters.
NASA / Hubble Space Telescope / ESA

Hundreds of Stellar Measurements

Jae-Woo Lee (Sejong University, South Korea) approached this drawback by creating a brand new photometric system to measure chemical abundances in carefully spaced stars. Lee’s system of narrow-band filters is designed to seize the absorption bands of the molecules CN, CH, and NH, that are essential for figuring out the abundances of carbon and nitrogen.

Lee utilized this photometric system to 842 red big stars in Messier 5, a globular cluster in the Milky Way that’s estimated to be greater than 12 billion years previous. Previous research of this cluster recommended that it’s residence to 2 populations of stars, one of which is enhanced in nitrogen.

A graph demonstrating how Jae-Woo Lee's new photometric system works
The new filters, some of that are proven in the blue and red traces in the prime panel, enable for higher isolation of essential spectral options.
Lee / Astrophysical Journal 2017

Application of the new photometric system revealed that Messier 5 consists of not two however three stellar populations. The extra exact photometry revealed that the nitrogen-enhanced inhabitants is actually two separate populations that differ in each their degree of carbon depletion in addition to their distribution inside the cluster. What does the presence of a number of stellar populations imply for the formation of Messier 5?

Three Stages of Formation

This consequence means that the stars in Messier 5 shaped in a number of levels fairly than . The writer means that the nitrogen-normal inhabitants is probably going made up of first-generation globular cluster stars, whereas the nitrogen-enhanced populations shaped later.

A graph showing the distribution of the four stellar populations in Messier 5
One of the nitrogen-enhanced populations (CN-sE) has a considerably completely different distribution inside the cluster than the different nitrogen-enhanced inhabitants (CN-sI) and the nitrogen-normal inhabitants (CN-w).
Lee / Astrophysical Journal Letters 2021

Specifically, Lee argues that the centrally concentrated inhabitants possible shaped in the dense internal areas of the cluster after the authentic highest-mass stars exploded as supernovae, whereas the extra evenly distributed inhabitants shaped considerably later out of gas containing smaller quantities of recycled supernova materials. This speculation explains the distributions of the two populations in addition to their chemical abundances.

Hopefully, this technique can be utilized to seek for a number of stellar populations in lots of different globular clusters — clearly, these objects aren’t so simple as they appear!


“Formation of Multiple Populations of M5 (NGC 5904),” Jae-Woo Lee 2021 ApJL 918 L24. doi:10.3847/2041-8213/ac1ffe


This submit initially appeared on AAS Nova, which options analysis highlights from the journals of the American Astronomical Society.

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