Galaxy Zoo Starburst Talk

bulge or clump?

  • fulkdj by fulkdj

    I'm new at this and I'm a little confused as to the difference between a bulge and a clump. I think a bulge is the center material of a galaxy but is it also considered a clump of stars? Or does the designation 'clump' only apply to off-center objects? Could you take me through the whole classification proccess on this so I can see if I'm getting it right? I'd hate to screw up the data and the cartoon drawings in the help section don't always corespond to the photos I see. Thanks.


  • KWillett by KWillett scientist

    No problem - the distinction between the two isn't always clear. The bright center part of the galaxy is what we're referring to as the bulge; it usually dominates the total stellar mass of the galaxy. In identifying "clumps" (which are smaller regions of stars and/or ionized gas), we're looking for two things. If a single bright clump isn't located at the center of the galaxy, that's evidence that the galaxy has been disturbed via a merger. If there are multiple clumps, it likely indicates either a merger in progress or (in more distant galaxies) the actual assembly and formation of galaxies via building up these clumps.

    I suggest clicking on the blue "Help" button in the upper right while you're classifying galaxies for both the "bulge" and "clumpy" tasks. There are a couple of actual images of example galaxies, rather than cartoons - this may help in distinguishing between bulges and clumps.