MWC 922 Nebula
Published on Apr 28, 2007 at 8:10 am.
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Filed under nebula, stars.
A team of astronomers led by Peter Tuthill (University of Sydney) and James Loyd (Cornell University) has found a rather remarkable nebula. It looks like a square! In fact, they have nicknamed the nebula the “Red Square.” Well, actually, it isn’t really square, but it sure looks that way in a photograph. In fact, the appearance is remarkably linear and symmetric — something not normally seen in a nebula. This particular image was created from images taken with the 200-inch telescope at Mount Palomar and Keck II at Mauna Kea.
As I said, this nebula isn’t really a square. Rather, it looks that way from our perspective. The star MWC 922 is a very hot (Be) star that is loosing mass in a bipolar outflow. That means that it is spewing gas out in a pair of conical outflows. Now, that isn’t all that uncommon. But, normally, these outflows don’t produce such complicated and symmetric appearing patterns as this. This apparent shape may be caused by a projection onto the outflowing gas from the central star. To get the apparent symmetries, a ring of material right near the star would shield part of the projection. The spokes seen in the image above may be the result of density ripples in that ring.
Now, all of this sounds very strange. But, we may have already seen something like this at a much more advanced stage of its development. When the Hubble Space Telescope imaged the location of supernova SN 1987A, astronomers were surprised to see the image below:
The small blob in the center of this image is the expanding supernova remnant. The bright ring in the middle and the outer rings to either side are remnants of prior events with the star. SN 1987A was a surprise in many ways. It was not the sort of star that astronomers had expected to blow up. In an earlier post, I said that recent models suggest that was because the progenitor star was actually a star formed from the merger of a close binary system. That event would have produced such an outflow, and the resulting star then went supernova. Here we see the conical bipolar outflows as well as a central ring that is expanding away from where the star was. Tuthill and Lloyd are the ones who actually brought up the similarities in these two stars and their strange outflows. Now, this doesn’t mean that MWC 922 is necessarily going to go supernova. Rather, it suggests that perhaps a similar sort of process may be going on with this star as had gone on with the progenitor star of SN 1987A. The similarities are striking, and this bears more research.
And, this also brings home something that I tell my students. The universe is a pretty big place, and in all of what is out there, most anything that can happen, does. And, whatever is going on with these two systems may or may not have the same root cause, but apparently has some similar physics going on. And that is interesting. I’d imagine that as our imaging technology gets better, we’ll be finding more of these sort of things.
-Astroprof
Images courtesy of Peter Tuthill (MWC 922) and NASA, HST (SN 1987A)
