Question: I’ve been looking at information about the largest known galaxy, IC 1101. Most sources say it is ~6 million light years in diameter but I can’t find any primary sources for this size estimate.
I was looking through research papers and the closest I could find to a direct measurement was 600kpc (so only about 2 million light years). There are lots of other figures mentioned around the internet but they just seem to have been pulled out of thin air!
I even tried measuring it myself using an image from Chandra, but I don’t think the usual trigonometry calculations work when objects are so far away and redshifted (I got a much smaller 150,000 light years as a result!)
I suppose my question is, how big is IC 1101 really, and how do we know?
Answer: You can get a pretty complete listing of the information available on just about any galaxy from the NASA Extragalactic Database (NED) at http://ned.ipac.caltech.edu/. You can use the object name search to look up the information for IC1101, where it lists in its “basic data” section that IC1101 has a major axis diameter of 1.2 arcminutes, which ...