When stars are torn from smaller, satellite galaxies by larger galaxies, they form thin streams, or tails. The streams collect either in front or behind the satellite galaxy as it orbits. During her March 22 lecture, “Tales from Tails”, Prof. Kathryn Johnston, astronomy, Columbia University, spoke about the importance of measuring and cataloging greater numbers of stars in order to determine more about their exact distribution in the galaxy.
Johnston created an analogy, saying that, “[the] same way the moon pulls on the earth and creates the ocean tides, you can get the Milky Way galaxy pulling on a satellite and creating tides on the satellite.”
Streams of stars reveal “fossil signatures.” Just as the earth contains evidence of species that once lived, streams contain matter which originated outside the galaxy. Therefore, “fossil signatures” are analyzed to gain knowledge on the details of the debris, the cause of star streaming and the origin of the galaxy.
Galaxies are structured in three parts; the bulge, disk, and stellar halo. The bulge is spherical in shape and holds the galactic nucleus, which is a super massive black hole. The disk, which transects the bulge, contains new and old stars, planets, dust and gas. The bulge and the disk make up 99% of the galaxy.
The remaining 1% consists of the stellar halo, which resembles a glowing halo, surrounding the more condensed structures of the bulge and disk. According to Johnston, the halo consists of “globular clusters,” or spherical condensations of old stars, including the oldest stars in the galaxy. Stellar halos also consist of the dwarf galaxies, or “satellite galaxies,” which contain significantly less mass than larger galaxies.
The instruments of star mapping are vital to understand the structure of the galaxy. Great achievements in the past decade have yielded a new vision of the galaxy, including a map of the halo of the Andromeda galaxy.
A large catalog of stars is crucial to produce, to read and to analyze stellar maps. This mapping process has discovered various structures in the Milky Way, including the 1994 discovery of Sagittarius, a constellation found within the dense core of the Milky Way.
In previous years, luminosity inhibited the production of maps. Solar luminosity is a unit of radiant power measured in watts. Recent advancements in technology have provided scientists with the instruments to see lower levels of stellar light from around the galaxy. Consequently, the number of recorded dwarf galaxies has doubled in the past decade.
This increasing data about dwarf galaxies has yielded new information about other galaxies in the local group, such as Andromeda, which connects to the Milky Way through the small satellite galaxies. This information may enlighten scientists about the formation of the galaxy and possibly, the entire universe.
Original Author: Caitlin Parker