Our galaxy, the Milky Way , is part of a region rich in constituents and full of activity and interest. What is usually thought of as our cosmic neighborhood is the Local Group , a region about 10 million light-years across that contains about 120 galaxies within it. The vast majority of these galaxies are dwarf and irregular galaxies, although there are some more notable members.
The largest galaxy in the local group is Andromeda , located about two million light-years from us , it is about twice as large, although it has a mass similar to that of the second largest member, the Milky Way . The third largest member is the Triangulum galaxy, with between 6 and 10 times fewer stars than its two older sisters, it could be a satellite of the Andromeda galaxy , although there are doubts about it.
The fourth member in size, mass and quantity of stars of the local group is the one that interests us in this article, the one that we have come to deal with: the Large Magellanic Cloud . This large cloud, which is actually a galaxy with a diameter of about 32,000 light years and about a hundred times less mass than the Milky Way, is the object that occupies the largest area in the night sky , after the disk of our galaxy itself, occupying about 20 times more than the full moon. It is for this very reason that it has been known , along with its companion, the Small Magellanic Cloud, since ancient times . However, because it is visible only south of 20º north latitude, its existence was not known in Europe until the Portuguese explorer Ferdinand Magellan wrote about it after his travels through the southern hemisphere at the beginning of the 16th century . He described the two galaxies as clouds, one larger and the other smaller, hence the name they are given today.
This cloud is located about 160,000 light-years from the Milky Way , making it one of the closest galaxies to our own. However, it is not entirely clear whether this galaxy and the Small Magellanic Cloud are true satellites of the Milky Way. Observations by the Hubble Space Telescope in 2006 seemed to suggest that these two dwarf galaxies were receding too fast to be gravitationally tethered to our galaxy . However, what we do know for sure is that these stars must have passed close to the disk of the Milky Way in the past, since a hydrogen bond has been detected that unites the three galaxies . This bridging is especially dense between the two dwarf galaxies, indicating that they have been gravitationally bound for a long time .
But even though these two galaxies appear to be billions of years old, as shown by these features but also by the presence of old red stars within them, they also contain regions of intense star birth . In the Large Magellanic Cloud is in fact the Tarantula Nebula, a gigantic nebula, with a radius of almost 1,000 light years , which is the region with the highest rate of star birth in the entire Local Group . It was at the edge of this nebula that the supernova known as SN1987A exploded , the closest supernova to Earth since Kepler was able to observe and study in the year 1604, which occurred in the Milky Way. This was the first supernova that modern astronomy was able to study in detail and directly, which is why it represented a huge advance in our understanding of these events and the last stages of the stellar cycle.
The Large Magellanic Cloud is sometimes classified as either a barred spiral galaxy or an irregular galaxy , and the truth is that it has a bit of both. It has a prominent core bar , which is an elongated region that extends beyond the central bulb. A faint but thick spiral arm emerges from this bar, the satellite galaxy showing a structure similar to that of other galaxies classified according to this criterion. However, it also shows regions that have an irregular geometry and do not follow the disk-shaped arrangement that would be expected of these spiral galaxies, although some rotation of the entire assembly has been measured with a period of about 250 million years , similar to that of the Milky Way itself.
The Large Magellanic Cloud has been described as an ” astronomical treasure “, due to the large number of different objects and structures it contains inside and that we can study with special ease given its proximity and that we do not see its light blocked by gas clouds and dust, as is the case with large regions of the Milky Way. In this galaxy at least 60 globular clusters, 400 planetary nebulae, 700 open clusters and of course hundreds of thousands of giant and supergiant stars have been observed.
If you want to locate this spectacle of nature in the sky, remind yourself that you will need a clear and very dark sky to really see anything with the naked eye. The Large Magellanic Cloud is located in the constellation of the golden fish and is approximately in the center of the triangle formed by Canopus, Rigil Kentaurus (alpha Centauri) and the star Achernar , the brightest in the constellation of Eridanus.
References:
Eric Chaisson, Stephen McMillan, 2017, Astronomy Today, Prentice Hall
