A little over a year ago, we told you about a very bright comet on its way that we'd see in late 2013. It turns out that Comet ISON is not quite the light show we expected; in fact, it may be a goner. As the comet slung around the sun over the last few days, its brightness waxed and waned until astronomers were scratching their heads. What happened? Phil Plait put together a video showing the comet's swing around the sun from the vantage of the NASA/ESA spacecraft SOHO.
You can see the comet head was so bright at the beginning it was saturating the SOHO detector, but then faded fast (I wrote a brief explanation of what you see in SOHO images in an earlier post). The other thing to note is that now, days later, the comet has faded substantially; there is no nucleus to be seen, and we can even see stars right through the comet (the image at the top of this post was taken on Nov. 30 at 20:42 UTC, and makes that clear; ISON is on the upper right and is now pretty well dispersed).
It appears that the comet underwent "disruptive event," or what we laymen would call a crash, but the data is far from conclusive right now. The comet sure seems to be dying, but as Dr. Plait says,
But who knows? When the comet started fading before perihelion I thought it might be dying, and I was more sure when it really smeared out. Then it came back, and we thought it survived, but now it’s looking more like that was a last gasp. This comet (and our estimation of what it’s doing) changes its story on an hourly basis, it seems.
Read a more thorough explanation of the data we have so far on Comet ISON at Bad Astronomy.