Q&A: Supernova Remnants and Neutron Stars

Q:
I viewed the "Time-Lapse Movie Of Crab Pulsar Wind" that I found posted at http://chandra.harvard.edu/photo/2002/0052/animations.html In particular, I downloaded the MPEG image ( http://chandra.harvard.edu/photo/2002/0052/combinedmovie.mpg) that can be accessed from that page and viewed it using Microsofts Windows Media Player 6.4.07.1112.

1. What I noticed is that there is a series of at least 5 repetitions of the expanding motion and it is as though the sequence were started each time from the same point in time. : Is the sequence a series of replayed shorter image sequences (similar to what one often sees with satellite images of cloud cover) or is each frame displaying an image taken at a later time?
2. I also noticed that the sequence is sometimes time distorted... a kind of speeding up in some instances.

A:

1. We have 7 sets of coordinated HST and Chandra observations, and so to produce a movie of reasonable length the sequence was looped several times. This also has the advantage of allowing the same sequence of images to be seen with varying degrees of magnification. Your analogy to looped weather satellite images is a good one.
2. This problem is almost certainly with the mpeg player on your computer. The format for the full-sized mpeg movie is large enough that some combinations of computers and mpeg software produce a somewhat jerky playback. The true interval between each of the steps in the combined movie is about 22 days, give or take a day.

These answers were provided by the scientist who produced the movie, Professor Jeff Hester of the Department of Physics & Astronomy at Arizona State University.