The Pleiades, or Seven Sisters, is an open stellar cluster that contains a glittering population of searing-hot B-Type stars. The Pleiades, less colorfully termed Messier 45 or M45, is one of the closest star clusters to our own planet, and it is also the cluster that is most easily observed with the naked eye–especially during the winter months–as it sparkles in the clear, dark, and star-blasted night sky in the constellation Taurus (The Bull). The cluster is dominated by very hot, blue, and dazzling stars that were born within the last 100 million years–a mere wink of the eye on stellar time scales. In August 2016, a team of astronomers announced their intriguing and important new observations showing that, like cosmic figure skaters caught in a fantastic pirouette, the stars of the Seven Sisters cluster are spinning–however, these celestial ice-skaters are twirling around at different speeds!
Astronomers for a very long time have wondered about what it is that determines the rotation rates of these sparkling stellar sisters. Now, NASA’s Kepler Space Telescope, during its second-life as the K2 mission, has helped astronomers obtain the most complete catalog of rotation rates for the stars in a cluster. This important information can enable astronomers to gain a new understanding about where and how planets are born around these distant stars–and how stars evolve as they age. 바카라사이트
Like the phoenix bird of Greek mythology, NASA’s Kepler Space Telescope got a second chance at “life”–despite a crippling malfunction that brought its primary mission to an end in May 2013. Rather than giving up on the spacecraft, whose original mission was to discover how often Earth-like exoplanets occur within our own Milky Way Galaxy, a team of astronomers and engineers succeeded in developing a new strategy. The resulting second mission of this plucky spacecraft, re-named K2, not only continued Kepler’s original search for distant Earth-like worlds in our Galaxy, but also introduced some new opportunities for astronomers.
“We hope that by comparing our results to other star clusters, we will learn more about the relationship between a star’s mass, its age, and even the history of its solar system,” explained Dr. Luisa Rebull in an August 12, 2016 NASA Press Release. Dr. Rebull is a research scientist at the Infrared Processing and Analysis Center at the California Institute of Technology (Caltech) in Pasadena, California. She is the lead author of two new papers and a co-author on a third paper about these findings, all published in the Astronomical Journal.
Twirling Sister Stars
The name of the Pleiades is derived from the ancient Greek, likely from plein (“to sail”) because of the cluster’s importance during the sailing season in the Mediterranean Sea. However, the name eventually became mythologized as the name of seven divine sisters who were the daughters of Pleione–hence, the designation Pleiades–or, alternatively, the “seven sisters.” Historically, the Pleiades were viewed as a group of “seven” sister stars: Alcyone, Atlas, Electra, Maia, Merope, Taygeta, and Pleione. It is generally thought that the name of the star cluster came first, and Pleione was created later in order to explain it.
The great Italian astronomer Galileo Galilei was the first astronomer to observe the Pleiades through a primitive telescope, called a “spyglass,”–the first of its kind to be used for astronomical purposes. Galileo discovered that the cluster contains many stars that are far too faint to be observed with the naked eye. He published his observations, including a sketch of the Pleiades showing 36 stars, in his Sidereus Nuncius in March 1610.
The cluster radius has a core of approximately eight light-years and the tidal radius is about 43 light-years. The cluster itself hosts more than 1,000 statistically confirmed members. However, this figure excludes unresolved binary stars. It is also dominated by bright, young, hot blue stars, up to 14 of which can be observed with the naked eye depending on local observing conditions. The total mass contained in the cluster is estimated to be approximately 800 solar-masses.
The Pleiades hosts many brown dwarfs, which are sub-stellar objects, frequently referred to as “failed stars”, that sport less than approximately 8% of our Sun’s mass. This basically means that brown dwarfs are not heavy enough for nuclear fusion reactions to occur in their cores, thus lighting their stellar fires. Therefore, puny little brown dwarfs are unable to attain true stardom status. Brown Dwarfs may account for up to 25% of the total population of the Pleiades–although they constitute less than 2% of the total stellar mass. Astronomers have made recent important discoveries in their efforts to detect and analyze brown dwarfs in the Pleiades, as well as in other youthful star clusters. This is because the youth of these sub-stellar objects render them bright and observable–while more elderly brown dwarfs, dwelling within older star clusters, have faded and grown very dim, making them considerably more difficult to observe and study.