Are these galaxies orbiting the Milky Way?

The Magellanic Clouds

The Magellanic Clouds are two irregular galaxies that share a gaseous envelope and lie about 22° apart in the sky near the south celestial pole. The Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) orbit the Milky Way once every 1,500 million years and each other once every 900 million years. The Magellanic Clouds are visible to the unaided eye in the Southern Hemisphere, but they cannot be observed from most northern latitudes. The LMC and SMC are 14,000 and 7,000 light-years in diameter, respectively- smaller than the Milky Way galaxy, which is about 140,000 light-years across. The Magellanic Clouds were formed at about the same time as the Milky Way, approximately 13 billion years ago. They are presently captured in orbits around the Milky Way galaxy and have experienced several tidal encounters with each other and with the galaxy. They contain numerous young stars and star clusters, as well as some much older stars. One of these star clusters contains R136a1, the most massive star known, with a mass 265 times that of the Sun. The Magellanic Clouds serve as excellent laboratories for the study of very active stellar formation and evolution. 

The Large Magellanic Cloud is the third closest galaxy to the Milky Way (after two smaller galaxies not visible to the human eye), and the Large Magellanic Cloud is thought by most astronomers to be orbiting the Milky Way. Although there is some uncertainty due to various methods of distance determination, the best current estimate puts the Large Magellanic Cloud at 150,000 to about 160,000 light-years away or about five or six times as far from Earth as Earth is from the center of the Milky Way. Other estimates have it as far as 180,000 light-years. Estimates vary from a few billion to perhaps 10 billion stars in this galaxy, at best no more than about one-tenth the mass of the Milky Way. The Clouds also have a number of notable features, such as the LMC's Tarantula Nebula, usually referred to as 30 Doradus, which is the largest star-forming region in our local group of galaxies. At the center of 30 Doradus is a dense, massive cluster of stars called R136, which, with an age less than about 2 million years, houses stars so young that even the most massive members have yet to finish their short lives. With the Hubble Space Telescope, it is possible for astronomers to study the kinds of stars, star clusters, and nebulae that previously could be observed in great detail only in the Milky Way galaxy.

The LMC maintains a very clear spiral structure in radio-telescope images of neutral hydrogen. Streams of neutral hydrogen connect them to the Milky Way and to each other, and both resemble disrupted barred spiral galaxies. Their gravity has affected the Milky Way as well, distorting the outer parts of the galactic disk. Aside from their different structure and lower mass, they differ from our galaxy in two major ways. They are gas-rich; a higher fraction of their mass is hydrogen and helium compared to the Milky Way. Both are noted for their nebulae and young stellar populations, but as in our own galaxy, their stars range from the very young to the very old, indicating a long stellar formation history. The metallicity of the Magellanic Clouds is much lower than that of the Milky Way. These lower metallicities align more closely with the conditions found in the early universe (before the evolution and deaths of stars could enrich the interstellar medium) giving astronomers an idea of the processes that might have been in action billions of years ago. 

Another important feature associated with the Magellanic Clouds is the Magellanic Stream. Extending halfway around the Milky Way, this is a tidal tail of gas that has been stripped from the Small Magellanic Cloud by interaction with either the Milky Way or the Large Magellanic Cloud (the actual culprit is still a topic of research). Besides being spectacular night-time objects, the Magellanic Clouds are popular targets for professional astronomers. In fact, they've been featured in more than 15,000 research papers. There are many reasons for their popularity, including their proximity. They are as nearby as galaxies can get, roughly 150,000 light-years for the LMC and some 200,000 light-years for the SMC. This means they are close enough to be studied in detail, yet far enough away that their stars can be approximated as being at uniform distances- unlike those of the Milky Way, where it can be difficult to see the forest for the trees.