Explore the Large Magellanic Cloud

Understanding the Milky Way's Galactic Satellite

magellanic clouds
The Large Magellanic Cloud (middle left) and Small Magellanic Cloud (upper center) over Paranal Observatory in Chile. European Southern Observatory

The Large Magellanic Cloud is a satellite galaxy of the Milky Way. It lies some 168,000 light-years away from us in the direction of the southern hemisphere constellations Dorado and Mensa.

There is no one discoverer listed for the LMC (as it's called), or its nearby neighbor, the Small Magellanic Cloud (SMC). That's because they are easily visible to the naked eye and have been known to skygazers throughout human history. Their scientific value to the astronomical community is immense: watching what happens in the Large and Small Magellanic Clouds offers rich clues to understanding how galaxies that are interacting change over time. These are relatively close to the Milky Way, cosmically speaking, so they offer detailed information about the origins and evolutions of stars, nebulae, and galaxies. 

Key Takeaways: Large Magellanic Cloud

  • The Large Magellanic Cloud is a satellite galaxy of the Milky Way, located some 168,000 light-years from our galaxy.
  • Both the Small Magellanic Cloud and the Large Magellanic Cloud are visible to the naked eye from southern hemisphere locations.
  • The LMC and SMC have interacted in the past and will collide in the future.

What Is the LMC?

Technically, astronomers call the LMC a "Magellanic spiral" type galaxy. This is because, while it looks somewhat irregular, it does have a spiral bar, and it was very likely a smaller dwarf spiral galaxy in the past. Something happened to disrupt its shape. Astronomers think it was probably a collision or some interaction with the Small Magellanic Cloud. It has the mass of about 10 billion stars and stretches across 14,000 light-years of space.

A portion of the Large Magellanic Cloud showing its many clusters and gas and dust lanes set against a nebula backdrop.
A portion of the Large Magellanic Cloud showing its many clusters and gas and dust lanes set against a nebula backdrop.  NASA/ESA Hubble Space Telescope

The name for both the Large and Small Magellanic Clouds comes from the explorer Ferdinand Magellan. He sighted the LMC during his voyages and wrote about it in his logs. However, they were charted long before Magellan's time, most likely by astronomers in the Middle East. There are also records of its sighting in the years before Magellan's voyages by various explorers, including Vespucci

The Science of the LMC

The Large Magellanic Cloud is filled with different celestial objects. It's a very busy site for star formation and has many protostellar systems. One of its largest starbirth complexes is called the Tarantula Nebula (due to its spidery shape). There are hundreds of planetary nebulae (which form when stars like the Sun die), as well as star clusters, dozens of globular clusters, and countless massive stars. 

Astronomers have identified a large central bar of gas and stars stretching across the width of the Large Magellanic Cloud. It seems to be a rather misshapen bar, with warped ends, likely due to the gravitational pull of the Small Magellanic cloud as the two interacted in the past. For many years, the LMC was classified as an "irregular" galaxy, but recent observations have identified its bar. Until relatively recently, scientists suspected that the LMC, SMC, and Milky Way would collide sometime in the distant future. New observations show that the orbit of the LMC around the Milky Way is too fast, and it may not ever collide with our galaxy. However, they could pass close together, the combined gravitational pull of both galaxies, plus the SMC, could further warp the two satellites and change the shape of the Milky Way. 

A view of the Large Magellanic Cloud and all its star formation regions (in red). The central bar stretches across the entire galaxy.
A view of the Large Magellanic Cloud and all its star formation regions (in red). The central bar stretches across the entire galaxy. NASA/ESA/STScI

Exciting Events in the LMC

The LMC was the site in 1987 of an event called Supernova 1987a. That was the death of a massive star, and today, astronomers are studying an expanding ring of debris moving away from the site of the explosion. In addition to SN 1987a, the cloud is also home to a number of x-ray sources which are likely x-ray binary stars, supernova remnants, pulsars, and x-ray bright disks around black holes. The LMC is rich with hot, massive stars that will eventually blow up as supernovae and then likely collapse to create neutron stars and more black holes.  

The expanding cloud of material spreading out from the site of Supernova 1987a as seen in visible light from Hubble Space Telescope and x-rays from the Chandra X-Ray satellite. NASA/Chandra/Hubble 

The Hubble Space Telescope has been used often to study small areas of the clouds in high detail. It has returned some very high-resolution images of star clusters, as well as star-forming nebulae and other objects. In one study, the telescope was able to peer deep into the heart of a globular cluster to discern individual stars. The centers of these tightly packed clusters are often so crowded that it's nearly impossible to make out individual stars. Hubble has enough power to do that and reveal details about the characteristics of individual stars inside the cluster cores. 

A globular cluster in the Large Magellanic Cloud
Hubble Space Telescope looked at the globular cluster NGC 1854 in the Large Magellanic Cloud. It was able to see individual stars at the heart of the cluster. NASA/ESA/STScI 

HST is not the only telescope studying the LMC. Ground-based telescopes with large mirrors, such as the Gemini Observatory and Keck observatories, can now make out details inside the galaxy. 

Astronomers have also known for quite some time that there is a bridge of gas that connects both the LMC and the SMC. Until recently, however, it wasn't clear why it was there. They now think that the bridge of gas shows that the two galaxies have interacted in the past. This region is also rich in star-forming sites, which is another indicator of galaxy collisions and interactions. As these objects do their cosmic dance with each other, their mutual gravitational pull tugs gas out into long streamers, and shock waves set off spasms of star formation in the gas. 

The globular clusters in the LMC are also giving astronomers deeper insights into how their starry members evolve. Like most other stars, the members of globulars are born in clouds of gas and dust. However, for a globular to form, there must be a lot of gas and dust in a relatively small amount of space. As stars are born in this tight-knit nursery, their gravity keeps them close to each other. 

At the other ends of their lives (and stars in globulars are very, very old), they die in much the same way other stars do: by losing their outer atmospheres and puffing them off to space. For stars like the Sun, it's a gentle puff. For very massive stars, it's a catastrophic outburst. Astronomers are quite interested in how stellar evolution affects cluster stars throughout their entire lives. 

Finally, astronomers are interested in both the LMC and the SMC because they are likely to collide again in about 2.5 billion years. Because they've interacted in the past, observers now look for evidence of those past meetings. They can then model what those clouds will do when they do merge again, and how it will look to astronomers in the very distant future. 

Charting the Stars of the LMC

For many years, the European Southern Observatory in Chile scanned the Large Magellanic Cloud, capturing images of the stars in and around both Magellanic Clouds. Their data were compiled into the MACS, the Magellanic Catalog of Stars. 

This catalog is mainly used by professional astronomers. A recent addition is the LMCEXTOBJ, an extended catalog put together in the 2000s. It includes clusters and other objects within the clouds. 

Observing the LMC

The best view of the LMC is from the southern hemisphere, although it can be glimpsed low on the horizon from some southerly parts of the northern hemisphere. Both the LMC and the SMC look like ordinary clouds in the sky. They are clouds, in a sense: star clouds. They can be scanned with a good telescope, and are favorite objects for astrophotographers. 

Sources

  • Administrator, NASA Content. “Large Magellanic Cloud.” NASA, NASA, 9 Apr. 2015, www.nasa.gov/multimedia/imagegallery/image_feature_2434.html.
  • “Magellanic Clouds | COSMOS.” Centre for Astrophysics and Supercomputing, astronomy.swin.edu.au/cosmos/M/Magellanic Clouds.
  • Multiwavelength Large Magellanic Cloud - Irregular Galaxy, coolcosmos.ipac.caltech.edu/cosmic_classroom/multiwavelength_astronomy/multiwavelength_museum/lmc.html.