Hubble Snaps Pix Of Dying Supernova

The Hubble has taken some great pictures of a supernova according to CNN. You can get a more indepth article, and more pictures from Space.com story on the same subject. Purty explosions!

Comments

Re:Semi-OT : Bigger Pictures?

[HellKrisp]

This big enough? :) (got from here)

Aspheric explosions

[Beryllium Sphere(tm)]

That passing line in the space.com article about lack of symmetry connects to some interesting physics.

Scientists were embarrassed for a while by the fact that the most realistic computer models of supernovae would fizzle instead of exploding. A simulated shock wave would start from the core, but with the mass of a star falling in on it the shock wave always stalled.

Then they switched from 1-dimensional simulations to 2-dimensional simulations when they got hold of enough computer power. Turns out there's an overturn instability. The shock wave can't make it out *on average* but does locally. Some small fluctuation gets bigger as the shock wave pounds at it and that direction gets more of the action.

Which explained an old observation that a lot of supernova remnants were moving pretty fast. Among other things, the supernova is a rocket engine with peak power equal to the luminosity of a galaxy, and (forgive me) astronomical amounts of propellant.

That was a qualitative insight from a quantitative increase in computer power.

Re:The amazing thing is the colours

[LMCBoy]

The colors in this particular image are especially misleading.

In most HST "pretty-picture" images, the colors are at least representative of reality. You take three images, through "blue", "green" and "red" filters, then stack them, with each layer driving the appropriate R,G,B value of the color composite. The result may be more saturated than reality, but you get at least some idea of how it would look to your eye.

However, this image is a stack of "narrow-band" images, centered on particular atomic emission lines. These narrow-band images are incredibly useful scientifically, because they let you study the energetics and chemistry inside the SN remnant, as well as the shock conditions of the gas. However, the colors are assigned arbitrarily, and have no connection to how the object would actually look.

Unfortunately I saw no caveat to this effect in either the CNN article (no suprise) nor the space.com article (mildly disappointing).

I mean, why not add a phrase in there like: "In reality, Cas A is not so colorful. The vivid colors are added to the image to help scientists map out different chemicals and their ionization states, which allows them to determine the strength of the original explosion, and how it has evolved to its present state."

Millions of Miles and a Metric Trick

[mattr]

Everyone knows light travels at 186,282 miles per second. At least I've known that since elementary school, nearly 30 years ago.

Multiply by 3600 sec/hour and you will see that one light-hour is about 671 million miles.

So if a supernova shockwave is moving at 45 million miles an hour, that's 45/671 or about 6.7% the speed of light in a vaccuum.

It works in metric too of course..
1 light-second is about 300,000 km/s (a third of a million km/s)
1 light-hour is then about 1000 million km/s, and 72/1000 or 7/100 gives you about 0.07c.

So next time you see a number of million kilometers per hour from CNN you can just divide it by ten and that is the percentage of the speed of light.

I think when we talk about this scale of velocity we need something better than "million miles/kilometers per second" and more tangible than a fraction of c.