By Eli Biran and Farah Abed
The team that discovered the twin galaxy PKS 0745-71 will be publishing its findings in the Astrophysical Journal in March, but the research has already been presented at a major physics conference in Mexico this past week.
The research team has dubbed the twin galaxies “Cow” and “Moose,” in honor of the fictitious Anakin Skywalker and Obi-Wan Kenobi from Star Wars fame, because they are young galaxies (one is about 500 million years old, the other is only about 200 million years old) and a natural choice for a name that sounds like a delicious high-calorie snack, but more importantly because they both share similar chemical makeup.
The research team discovered the two galaxies a decade ago, and although they have studied them for years, they discovered a recent piece of evidence that a fifth member of the group has just joined the galactic family.
Cow and Moose are small and red-shifted, like other small galaxies, which is normal for galaxies of their age. But there was a surprise. Because of the close proximity of the newly discovered galaxy, the gravitational influence of the galaxy has altered the orbit of the other four members, who are now at a greater distance from each other than they have been in the past. This new addition has significantly altered the mutual distribution of elements such as carbon, oxygen, and iron.
According to Seth Epps of Dartmouth College, the research team’s lead author, “We are not sure if this is just due to the interaction of these newly discovered galaxies, or if there is something about the makeup of this fifth galaxy that can disrupt the behavior of the four. This suggests that all small galaxies are not created equal.” As the name “Cow” suggests, it is a pretty big entity, with a larger diameter and larger mass than the other four galaxies.
According to the research team’s lead theorist, Roger Davies of the University of Hertfordshire, “We can’t tell if there are any stars in the satellite galaxy, but there is a pretty large gas cloud that looks like it contains at least one star.”
The team has not come to any conclusions about the nature of the fifth galaxy, but believes it to be either a star or a dwarf galaxy. They estimate it is about 20 to 40 million light years from Earth. Not everyone agrees that there is a fifth galaxy within the group, but some believe that there may be multiple planets of different sizes and compositions surrounding the Milky Way that are yet to be discovered, or that the true fifth galaxy is a collection of stars embedded in the galaxy known as the Local Group. Regardless, this is a unique observation and researchers plan to continue to observe the area with the Hubble Telescope in order to better understand what is happening.
Sources: http://www.bbc.co.uk/news/science-environment-40467051 http://en.wikipedia.org/wiki/Galaxy_PKS0745-71#_ga=1.4124244530.00628001630.c5c8b53f7db9 https://go.nasa.gov/2r2nKh