The globular cluster age distribution of the Large Magellanic Cloud exhibits a puzzling gap from ∼4 to 10 Gyr ago, with an almost total absence of globular clusters. Within this age gap, only two confirmed globulars have been identified. Residing all the way over in Pictor, at a projected angular separation of ∼10° from the LMC centre, globular cluster ESO 121-03, with an age of approximately 9 billion years, was until 2022, the only known globular that formed during this vast ~6-7 billion “age gap” between the two bursts of cluster formation. However, in January 2022 astronomer Andrés E. Piatti confirmed the existence of a second one – KMHK 1592 with an age of approximately 8 billion years – which is located in the LMC outer disc.

One of only two members of the exclusive “Age Gap” club, remote ESO 121−03 lies in the far northern outskirts of the LMC. DSS image

The Cloud also hosts the only known gravitationally bound binary globular cluster system – NGC 2136 and 2137. The cluster centres of gravity have an angular separation of only about 20 pc = 1.34 arcmin, both have similar ages, of about 100 ± 20 Myr, and identical metallicity, and their orbital period is about 46 Myr, which means they have orbited each other about twice within their lifetime (S. F. Portegies Zwart, S. P. Rusli 2006). The most likely fate of this system is to merge into a single structure.

It is a unique and striking sight to observe the only known gravitationally bound binary globular cluster system. NGC 2136 is the larger of the two, NGC 2137 the smaller. DSS image

There is a superb quartet of young globular clusters in a rich 16′ starfield in the southeast of the LMC of which three – NGC 2156, 2159 and 2172 – are coeval. Their age (65 million years) is consistent with their star formation being triggered by the expulsion of residual gas from the quartet’s fourth member, NGC 2164 (98 million years old).

These four globular clusters are a superb sight, quite apart from their formation history. DSS image

NGC 1850 is an unusual double cluster that lies in the bar of the Large Magellanic Cloud. Not only is NGC 1850 the brightest star cluster in the Cloud, but it also has a tiny companion cluster, NGC 1850A, lying 30″ west of centre. Both are very young. NGC 1850 is ~50 million years old and NGC 1850A, composed of extremely hot, blue stars and fainter red T-Tauri stars, is a mere 4 million years old.

The spectacular filigree pattern of diffuse gas visible in the image was formed millions of years ago when massive stars in the main cluster exploded as supernovae. The nebula is part of the N103 superbubble and looks similar to the well-known supernova remnant, the Cygnus Loop, in our own Milky Way.

In 2021, a team of astronomers led by Sara Saracino of Liverpool John Moores University, U.K, reported the detection of a black hole in NGC 1850. Named NGC 1850 BH1, the black hole has a mass of 11 solar masses and is part of a binary system; its companion is a main-sequence turn-off star with a mass of 4.9 solar masses. It is a semi-detached system, with a short period of 5.04 days and orbital inclination at a level of 38 degrees.

NGC 1850 and its small companion, lower right. Credit: ESA, NASA and Martino Romaniello (ESO)

Larger galaxies cannibalise smaller galaxies who are foolish enough to wander too close by. In 2021, a team of astronomers led by Alessio Mucciarelli of the University of Bologna in Italy, found evidence that the Large Magellanic Cloud had cannibalized another galaxy at some point in its mysterious past. (The research, titled “A relic from a past merger event in the Large Magellanic Cloud”, was published in Nature Astronomy.)

The chemical composition of the stars in NGC 2005 differs from other stars in the Large Magellanic Cloud. They compared the metallicity of the stars in NGC 2005 with 10 other globular clusters in the LMC, and with 15 older globular clusters in the Milky Way. NGC 2005’s metallicity are significantly lower than the other globular clusters in the Large Magellanic Cloud and older ones in the Milky Way, which suggests a different history. So the team ran simulations to see how such a wildly different cluster could have turned up in the LMC. The best fit was a different galaxy entirely, very similar to the existing ultra-faint satellites. Over billions of years, that mysterious ghost galaxy was pulled apart and most of its stars spread around. But not the core; it remained largely intact, leaving NGC 2005 as the last evidence that the galaxy ever existed. “NGC 2005 is the surviving witness of the ancient merger event that led to the dissolution of its parent galaxy into the Large Magellanic Cloud, the only known case so far to be identified by its chemical fingerprints in the realm of dwarf galaxies,” the researchers write.

Ancient globular cluster NGC 2005 is the unique surviving relic of a dwarf galaxy that merged into the LMC in the past. Image credit ESA, Hubble

And to top off observing the Cloud’s globular clusters in spectacular fashion, one can even observe a “globular of the future” – the spectacular NGC 2070 at the heart of the Tarantula Nebula! Its stellar inhabitants number roughly 500,000 and at its heart lies the compact cluster R136 which has birthed an overabundance of some of the most massive stars ever found, including R136a1, a Wolf-Rayet star which, with a weight of 215 solar masses, is the most massive star in the known universe.

Clusters such as NGC 2070 have such an exceptionally high concentration of massive stars that they are referred to as super star clusters. They are rare examples of the super star clusters that formed in the distant, early universe, when star birth and galaxy interactions were more frequent. Containing hundreds of thousands to millions of young stars usually within less than a few parsecs, they are likely the progenitors of globular clusters.

The stars of most young clusters drift away into the field star population within a few tens of millions of years, whereas the super star clusters have enough mass to stay together for the long run, and NGC 2070 is one of the best candidates to hold together and eventually become a young globular cluster. (We have only one such monster object within our own Galaxy that we know of – Westerlund 1 – which lies obscured behind a large cloud of dust and gas in the constellation Ara; an extremely difficult object to observe.)

NGC 2070, the heart of 30 Doradus, wherein reside some of the largest stars known thus far in the universe. Credit: ESO, Hubble

Limited to our two dimensional view of the sky, it is impossible to envision the three dimensional reality of the Cloud. But one can try by demarcating naked eye where the galaxy’s three most far-flung globular clusters are projected on the sky. These three globular clusters are located so far from the centre of the LMC that they appear as isolated stellar systems in the southern sky.

Reticulum Globular, which resides in Reticulum as its name implies, lies at a projected angular separation of ~11° from the LMC’s centre.

ESO121 03, which resides in Pictor, lies at a projected angular separation of ∼10° from the LMC’s centre.

NGC 1841, residing in Mensa, lies at an astounding projected angular separation of 14.5° from the LMC’s centre. (Not only is it the LMC’s most far-flung globular cluster, but it also happens to be the southernmost globular cluster in our night sky.)