Comments on: Blobs excited by hot flashes

By: Echoes and Screams in Space « One Astronomer’s Noise

Echoes and Screams in Space « One Astronomer’s Noise — Tue, 17 Mar 2009 06:01:52 +0000

[...] Bad Astronomer shows a really cool Spitzer image of the region around Cassiopeia A, a supernova remnant (and one of the first things our little radio telescope could see!), and the [...]

By: Tom Marking

Tom Marking — Mon, 06 Oct 2008 18:27:28 +0000

O.K. I did a little bit more reading and I think I’ve got this one figured out. According to Wikipedia the actual supernova remnant is about 10 light-years across (i.e., radius = 5 light-years). So 160 light-years is way beyond the wavefront of the expanding debris. The hot blobs 160 light-years behind the supernova are part of a nebula whose structure has NOTHING to do with the supernova explosion, it was pre-existing. That’s why there doesn’t have to be a ring of hot IR emission centered around the supernova source.

It also explains why the blobs may appear so bright to us. The nebula is behind the supernova and the hot blobs are those points where the spherical wavefront of X-rays/gamma rays/etc. intersect the nebula. There does not have to be a lot of gas and dust between us and the blobs. It could be relatively empty interstellar space which explains why the blobs appear so bright to us.

By: Kim G

Kim G — Fri, 03 Oct 2008 17:00:12 +0000

I admit I have no idea how long gamma or x-rays can maintain their coherence over that kind of distance. Neither do I know much about the reflective abilities of electromagnetic radiation in general. Is it even possible?

That dust must be toast by now, though. Hm…I’m seeing the announcement of a new particle on the horizon– toasty-dust!

By: Tom Marking

Tom Marking — Fri, 03 Oct 2008 14:56:34 +0000

“Wow, you wouldn’t think mere dust would be so reflective as to allow light to “survive” that much time and distance without diffusing into nothing.”

I don’t think they’re talking about actual reflection of either visible light or infrared. Instead, if I read the original post correctly it was the X-rays, gamma rays, etc. from the initial supernova explosion going away from us and hitting gas, dust 160 light-years behind it, heating it up, and then causing it to glow in the infrared because it’s hot. Of course, for us to see the infrared glow that electromagnetic radiation must pass through 160 light-years of dust and gas on the far side and presumably another 160 light-years of dust and gas on the near side before it gets to us. So it’s surprising it’s as bright as it is. That’s why I’m skeptical of that particular explanation.

By: Kim G

Kim G — Fri, 03 Oct 2008 13:31:10 +0000

Brian Hodges wrote:
“Wow, you wouldn’t think mere dust would be so reflective as to allow light to “survive” that much time and distance without diffusing into nothing.”

Nah. Brian that’s what we call “an inconvenient truth”. Little facts about super-charged dust that doesn’t cool even after 300 years can’t be allowed to get in the way of the theory!

Ignore at will.

Ok. don’t ignore. It’s a good question. Maybe Phil has some ideas on that.

By: Jose

Jose — Fri, 03 Oct 2008 12:05:35 +0000

It’s because were looking at infrared light, which can get through the dust. If we had Spitzer in 1680, we could have viewed the supernova directly in the infrared. It’s not spherical because the blobs aren’t evenly distributed.

By: Tom Marking

Tom Marking — Thu, 02 Oct 2008 21:11:52 +0000

What I don’t get about this article is this. If the blobs are 160 light-years behind Cassiopeia A doesn’t that mean there is an extra 160 light-years worth of dust and debris that light has to travel through? Wouldn’t that cause them to be much dimmer and perhaps invisible? I’m not sure why there are separate blobs either. If the supernova explosion was roughly spherical and you take a plane 160 ly behind it and intersect the sphere, you get a circle. So why isn’t there a bright circle centered on Cas A?