Starship Asterisk*

APOD: 2005 October 25 - Supernova Remnant N132D in Optical and X Rays
http://apod.nasa.gov/apod/ap051025.html

In the description for the referenced APOD, it was written "The expanding shell from this explosion now spans 80 light-years and has swept up about 600 Suns worth of mass."

I do not understand what is meant by "swept up about 600 Suns worth of mass." How and where was this matter that was "swept up?" Surely, there could not have been 600 sun-like stars within that 80 ly sphere!

RJ Emery wrote:APOD: 2005 October 25 - Supernova Remnant N132D in Optical and X Rays
http://apod.nasa.gov/apod/ap051025.html

In the description for the referenced APOD, it was written "The expanding shell from this explosion now spans 80 light-years and has swept up about 600 Suns worth of mass."

I do not understand what is meant by "swept up about 600 Suns worth of mass." How and where was this matter that was "swept up?" Surely, there could not have been 600 sun-like stars within that 80 ly sphere!

You are right, there weren't 600 Sun-like stars within that 80 ly sphere.

But there might very well have been a lot of gas and dust there. The supernova in question exploded in the Large Magellanic Cloud, and we know that the LMC is a gas-rich galaxy.
Consider this man walking in a blizzard. There is snow all around him. If he himself was a huge "snowplow" that could sweep up all the snow around him while he walked for, say, 80 miles (and supposing that the blizzard went on for 80 miles), he would sweep up a lot of snow.

Ann

I think it means that the mass within the expanding shell is estimated to be equivalent to about 600 Suns.

For comparison, I just made a rough estimate of the total mass of the 80 stars within 40 light-years of Earth, and came up with a mass of about 90 Suns. So, ignoring planets/gas/dust (and possibly dark matter) in our vicinity, I suppose this portion of the LMC is at least 6 times more dense than the equivalent volume of space surrounding Earth.

In the absence of any other information, I might guess that the 600 solar masses within the remnant, includes dark matter, which is supposedly 5.5 times more abundant in the known universe, than ordinary matter.

(The mass of planets, gas and dust must surely be a tiny component of the total mass of ordinary matter.)

Nitpicker wrote:In the absence of any other information, I might guess that the 600 solar masses within the remnant, includes dark matter, which is supposedly 5.5 times more abundant in the known universe, than ordinary matter.

(The mass of planets, gas and dust must surely be a tiny component of the total mass of ordinary matter.)

The dynamics of dark matter at scales smaller than galactic halos is poorly understood. I think they're talking about ordinary matter, the total mass of which is almost entirely accounted for by stars, gas, and dust.

Another comparison (which doubtless highlights how hopeless my guesses can be) is that the Orion Nebula, M42, is thought to be only 24 light-years across, yet contains an ordinary mass of about 2000 Suns. I suppose local density variations can be larger than I originally imagined.

APOD: 1996 May 9 - Supernova Remnant: Cooking Elements In The LMC
APOD: 1999 Sep 13 - Supernova Remnant N132D in X Rays
APOD: 2002 May 23 - N132D and the Color of X-Rays