Can there be anything more incredible than being able to resolve hordes of fabulous stars in another galaxy, never mind some of the most extreme stars ever seen?

It’s no surprise that the truly extreme stars all inhabit the Cloud’s most extreme piece of real estate… the ferocious 30 Doradus complex. These stars, the hottest, most massive, and most extreme stars known, are reminiscent of the early universe. The LMC’s proximity and clear global view makes it the only example of a starburst (an extremely intense and rapid episode of star formation) that astronomers can study in detail, making it the Rosetta Stone that can help provide astronomers with the key for understanding our universe’s history.

Being able to delve into this incredible region and observe some of these extreme stars among the hordes of stars inhabiting 30 Doradus is dumbfounding.

Another extreme star, red supergiant WOH G64, resides far from 30 Doradus; it lives in supergiant shell LMC 6. The star earned its place in history in October 2024 when a team of astronomers published an image of it… the first detailed interferometric image of an RSG outside the Milky Way. It is an extremely large star 1540 times the size of the Sun – easily the largest in the LMC! Unfortunately, this highly massive and luminous star is extremely faint at mag 17-7-18.8. You can read a fascinating write-up about this extreme star here. 

S Doradus is arguably the most fabulous star we can observe in the Large Magellanic Cloud. Not only is it the brightest star in the Cloud (visual magnitude 8.6 to 11.7), and one of the brightest known stars (absolute magnitude -9), but it is the prototype for one of the rarest types of star known – luminous blue variables (also called S Doradus stars). It lies in the OB Association LH 41 = NGC 1910 which is located on the northern rim of the central bar of the Cloud, and contains a number of other extremely bright stars.

S Doradus is a blue supergiant with a spectrum very similar to that of P Cygni, another variable of the same type. These stars are extremely massive (at least 60 solar masses) and luminous, and they use up their nuclear fuel so fast that their lifetimes can’t exceed a few million years before they explode as supernovae, and they are therefore extremely rare. The very high luminosity also results in an enormous radiation pressure at the star’s surface, which tends to blow away significant portions of the stellar mass by way of an intense stellar wind and, occasionally, in the form of an ejected gaseous shell. According to Burnham, the light curve of S Doradus also points to a long period (40-year) eclipsing variable behaviour.

And for the science fiction aficionados, in 1952 A. E. van Vogt marooned a pair of young lovers on a planet around S Doradus! Their rescuers commented on the star thus, “This star-type is so immensely hot that practically all of its energy radiation is in the far ultravisible. The normal radiation of that appalling star-type – the aeon-in-aeon-out rate – is about equal to a full-fledged Nova at its catastrophic maximum of violence. Nova O, we call that brightest of all stars; and there is only one in the Greater Magellanic Cloud, the great and glorious S Doradus.” It is indeed a great and glorious star.

The two Magellanic Clouds’ Classical Cepheids (also known as δ Cephei stars or type I Cepheids) have a huge place in the history of astronomy, and no exploration of the LMC would be complete without observing at least one of them. And fortuitously, one is exceptionally well-placed for an observation, being just north of bright and beautiful Theta Doradus!

In 1912, Henrietta Swan Leavitt, working as one of the famous computers at Harvard College Observatory, made a discovery that was to become one of the cornerstones of modern astronomical science. She was studying photographic plates of the Large and Small Magellanic Clouds and compiled a list of 1,777 periodic variables. She classified 47 of these in the two Clouds as Cepheid variables and noticed that those with longer periods were brighter than the shorter-period ones. She correctly inferred that as the stars were in the same distant Clouds, they were all at much the same relative distance from us. Any difference in apparent magnitude was therefore related to a difference in absolute magnitude. When she plotted her results for the two Clouds, she noted that they formed distinct relationships between brightness and period. She chose 25 variable stars from the Small Magellanic Cloud and in 1912 she published a diagram of this relation. Her plot showed what is now known as the period-luminosity relationship. The discovery of this simple and hitherto-unknown relationship made it possible, for the first time, to calculate their distance from Earth. Henrietta Leavitt had just become, in the words of George Johnson, author of the book Miss Leavitt’s Stars, ‘the woman who discovered how to measure the Universe’. Nowadays, the two Magellanic Clouds are also important targets for studying Classical Cepheids stars because both galaxies contain the largest known collection of these stars among all stellar environments, including the Milky Way.

Henrietta Swan Leavitt: the woman who discovered how to measure the Universe. Popular Astronomy, v. 30, no. 4, April 1922

For the variable star aficionado, the LMC is the place to be. Volume 5 of the General Catalogue of Variable Stars (5th edition) lists 4,802 known variables in the Large Magellanic Cloud – a number expected to increase enormously in the aftermath of the MACHO Project.

In February 1987, AAVSO member, Albert Jones in Nelson, New Zealand turned his telescope to look at the three variable stars he was studying in the LMC. There in the same viewing field was a very bright blue star that did not belong! Jones got his star charts out and noted the position of the new star relative to other stars. Clouds rolled in before he could determine a magnitude estimate, so he alerted other observers to his find. Later the clouds broke, and Jones was able to estimate a magnitude of 5.1. Not knowing if other observers were clouded out, he continued observing the supernova for another 4 hours. His perseverance provided critical early coverage of Supernova 1987A!

Nicholas Sanduleak (1933-1990) was an American astronomer who published a catalogue of stars in the Large Magellanic Cloud (1970) which included the progenitor of the Cloud’s famous 1987 supernova… blue supergiant Sk -69 202. He has a star in the Cloud named after him; it’s a peculiar symbiotic star that produces the largest stellar jet known thus far. Alas for being a very faint mag 17.0… a big Dobs star. 

Sk -69 202 became the coolest star in the LMC when it blew itself to smithereens in 1987 and gave us SN1987A. Credit: ESO

There it something incredibly fascinating about looking at a star that is a massive, short-lived blue star emitting copious amounts of high-energy ultraviolet photons and ionising a significant part of a huge cloud of gas! Where possible with the Henize nebulae, I have included the ionising stars on the annotated images.

In our own galaxy, double stars offer both charm and challenge. Like snowflakes, no two double-star systems are alike, and many pairs display beautiful contrasting colours and/or magnitude contrasts, while others are so close together that splitting them is a great visual test of one’s optics and of the night’s seeing conditions.

The Cloud’s double stars also offer charm and challenge. Albeit we have no chance of seeing the shimmering yellow and vivid blue colours of a LMC Albireo, the fact that we can split double stars and see magnitude contrasts in a binary star system 163,000 light years away in another galaxy makes the dazzling colour contrast a moot point.

Wolf-Rayet stars are an exotic class of very rare stars. They stars represent the most advanced evolutionary stage in the lives of luminous massive stars. And for very massive stars, mass loss dominates their evolution and Wolf-Rayet stars shed mass rapidly by means of very powerful stellar winds up to 10 million kilometres per hour (6 million miles per hour), causing them to dwindle at a rapid rate. Their mass is being blown away at a rate of 10 solar masses every million years, which means the equivalent of three Earths’ worth of material each year is blown away from the star at a speed that is about 3,500 times as fast as a bullet fired from a rifle.

Due to the extreme mass loss, WR stars are basically stripped-down versions of highly evolved massive stars. The exposed core equals between 10 and 20 solar masses and are extremely hot with surface temperatures between 25,000 and 60,000 K, and in extreme cases even as high as 90,000 K. They are extremely luminous, their luminosities ranging between about 100,000 and a million times that of the Sun, at the limit close to that of luminous blue variables.  (Luminosity is a measure of the total amount of energy radiated by a star or other celestial object per second… the power output of a star.)

Wolf-Rayet stars’ spectra show strong, broad emission lines. This implies copious amounts of ionized helium, carbon, oxygen and nitrogen in their rapidly expanding envelopes. As such, Wolf-Rayet stars are divided into 3 classes based on their spectra, the WN stars (nitrogen dominant, some carbon), WC stars (carbon dominant, no nitrogen), and the rare WO stars with C/O < 1. WO stars are believed to be Wolf-Rayet stars that have evolved past the WC stage.

As a result of their high fuel-burning rate and their rapid shedding of outer material, Wolf-Rayet stars are incredibly short-lived, lasting around a million years or even as little as just a few 100,000 years, which makes them incredibly rare stars. The fate of Wolf-Rayet stars, like that of all massive stars, is to explode as supernovae. These spectacular stars perfectly exemplify the endless cycle of stellar life and death that has molded the development of galaxies over billions of years… who can’t be dumbfounded at the sight of them in another galaxy?

In all this swirling nebulosity, Wolf-Rayet Brey 40a has blown a bubble around itself, and one can observe the visible fragments of its ring as ethereal and dagger-thin streaks to the south and west of the lovely mag 13.4 star. Credit: Y. Naze, G. Rauw, J. Manfroid, J. Vreux (Univ. Liege), Y. Chu (Univ. Illinois), ESO