Astronomers discover an ancient ultra-weak and metal-poor star cluster

An international team of astronomers reports the discovery of a new star cluster (SC) as part of the DECam Local Volume Exploration (DELVE) survey. The newly discovered cluster, dubbed DELVE 6, is ultra-faint, metal-poor, and estimated to be about 9 billion years old. The finding was detailed in a paper posted June 7 on the arXiv preprint server. In general, SCs are large gravitationally bound groups of stars. They are perceived as important laboratories for studying the evolution of stars and the clusters themselves. SCs are also good trackers for exploring the structure of the Milky Way. It is estimated that the Milky Way may contain around 100,000 star clusters. The researchers surmise that many undiscovered clusters are still hidden in dense stellar regions.

Now, a group of astronomers led by William Cerny of Yale University has found another star cluster, not in our galaxy, but on the outskirts of the Magellanic Clouds (MC). Detection was performed via matching filter searches on Dark Energy Camera (DECam) images processed as part of the DECam Local Volume Exploration Survey Second Data Release (DELVE DR2). “In this Letter, we present the most recent discovery in this ongoing census of Magellanic satellites: DELVE 6, an ultra-faint ancient star cluster on the distant outskirts of the MCs,” the astronomers wrote in the paper. DELVE 6 (or DELVE J0212-6603) is located about 261,000 light-years from Earth, 65,000 light-years from the center of the Small Magellanic Cloud (SMC), and about 114,000 light-years from the center of the Large Cloud. of Magellan (LMC). However, despite this relative proximity, DELVE 6 lies beyond the tidal radius of the LMC due to the Milky Way and the tidal radius of the SMC due to the LMC. This finding suggests that MCs as the two possible hosts have a weak gravitational influence on DELVE 6 and that this system cannot be confirmed to be associated with either Cloud.

According to the study, DELVE 6 has a half-light radius of about 32.6 light-years, a metallicity of less than -1.17 dex, and an absolute magnitude of -1.5 mag. The group is estimated to be at least 9.8 billion years old. Thus, if the association of DELVE 6 with MC is confirmed, it may be only the second or third ancient SC associated with SMC, or one of fewer than two dozen ancient clusters associated with LMC. The astronomers noted that DELVE 6 may also be a halo star cluster distant from the Milky Way. They added that follow-up spectroscopic observations are required to shed more light on the properties and origin of DELVE 6. Summarizing the results, the paper’s authors underlined that the observational census of ultraweak systems in the MC environment is still incomplete. “Considering the continued discovery of similar ultra-faint star cluster systems near the MCs in recent years, we speculate that a more extensive population of ancient, ultra-faint, metal-poor star clusters may exist around the LMC, SMC, and perhaps even others. . low-mass galaxies in the Local Group, waiting to be discovered by current and future studies,” the researchers concluded.