 At the turn of the 20th century, astronomer Harlow Shapley, studying a large number of R. R. Lyra stars inside globular clusters, found that the center of the galaxy was far from the Sun. He mapped 93 globular clusters. They formed a spheroidal shape with their own center, not near the Sun. He concluded that these giant clusters formed the bony frame of the galaxy. This area around the disk is called the galactic halo, or corona. It holds a large number of old stars and 158 globular clusters. The galactic halo itself has a diameter of at least 600,000 light-years, based on the locations of the globular clusters, although it may extend much further. In 2007, using 20,000 stars observed by the Sloan Digital Sky Survey, an international team of astronomers discovered that the Milky Way halo is a mix of two distinct components, rotating in opposite directions, the outer halo and the inner halo. Then in 2018, a team of astronomers analyzed 7 million stars from the Gaia mission and found that 30,000 of them were moving counter to the normal Milky Way flow. Our motions and composition profiles indicated that they came from a different galaxy. They called this new galaxy Gaia Enceladus. Using computer models for galaxy collisions, they estimated that it collided with the Milky Way around 10 billion years ago. This is a computer simulation of the merger. Here we see that Gaia Enceladus is now our galaxy's inner halo. On September 24, 2012, Chandra found evidence that the Milky Way galaxy is embedded with a large amount of hot gas in the halo. Counting this vast amount of gas, the mass of the halo is estimated to equal the mass of the stars in the galaxy. But as massive as it is, the amount of matter in this hot gas is not nearly enough to explain the galaxy's rotation curve. Large matter, or a new theory of gravity, is still needed. In 2018, using both Hubble and Gaia data on globular clusters, sizes and velocities, the mass of our galaxy was estimated to be at least 1.5 trillion times the mass of our sun. This is more than previous estimates and indicates that the Milky Way is among the universe's larger galaxies.