"Keenan's Ring" is the name we're giving to a giant starless cloud of hydrogen discovered near the Triangulum galaxy, M33. This is the largest, most massive hydrogen cloud discovered in the region since Wright's Cloud in 1979. In angular size it's about as large as the hydrogen disc of M33 (five times larger than the full Moon) and it's just been sitting there all this time, but it's so faint no-one had noticed it before. Well, not quite, but no-one realised just how large it was or that it was a ring.
Why does this matter ? Well, we don't have a good explanation for this object. The nearby Wright's Cloud is thought to be part of the much larger Magellanic Stream, but there's no obvious reason why there should be two large clouds at the end but offset at right-angles to the stream. Nor is it obvious why this one should be a ring - there's no particular reason to expect the gas to be missing in the centre of the structure. It's not likely to be a dark galaxy either (an object made of dark matter, gas, but without stars), because the velocity width is much smaller than would be expected. On the other hand, it does have a small velocity gradient, suggesting that it is a single coherent structure and not a chance alignment of lots of smaller clouds. It really is a mystery.
The figure shows the 3D data cube obtained with five years of Arecibo observations. The third axis is velocity, not distance (see link for details). Colours are chosen just to highlight different structures : blue for the Milky Way, red for everything else. The data looks noisy at one end but this is just because of how the data was processed. Keenan's Ring can be seen in this noisy red part of the data, but there are better images in the linked post.
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I want to know what the molecular gas can tell us about your ring, but it's too far north for my usual telescopes too. How very frustrating.
ReplyDeleteGreat work, team, I can't wait to dive in and read the full paper in a few days.
Aleksander Suchanowski Probably no black holes here - see linked article for details. Unless it was really really close (within our own galaxy), the hole in the ring would be much larger than what gas orbiting a black hold would look like.
ReplyDeleteCatherine Braiding Thanks ! Molecular gas observations are something people here keep suggesting, probably because they reaaaally want ALMA time. :) Wright's Cloud might be a better target since it's much more massive.
Branes...
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