Light from supernova remnants

[davhei]

Yesterday I was observing the Veil, a glorious sight. Amazing when it appears out of nowhere, distinct as can be, when putting a OIII filter in.

I started thinking about the physics behind the light from the supernova remnant and was hoping for some input from people with more knowledge.

Various sources seem to indicate that the progenitor star towards the end of its life blew away matter in a sort of bubble around itself with strong solar wind. When the star went supernova 8000 years ago the shockwave expanded outward and eventually hit the matter outside the bubble and energized the particles, causing them to emit light. In effect meaning the nebula glows because of the shockwave, expanding into the interstellar medium even today, 8000 years later.

The nebula is approximately 100 ly across however and I did a bit of calculating on the required velocity for the shockwave to reach 50 ly in 8000 years, concluding it would be close to 1900 km/s. Could very well have messed up the numbers though.

Now this seems very high. The sources I found mentioned shockwave speeds of between 40 km/s and 170 km/s. Scientists measuring the speed of the shockwave from supernova remnant W44 came up with 12.9 km/s. 1900 km/s is a far cry from any of these.

So I can’t understand how the shockwave could have an impact over the distances involved. Radiation from the explosion must have reached 8000 ly by now and couldn’t actively reshape the nebula as we see it now could it?

Would really appreciate some input on the mechanisms that make supernova remnants glow. Would add another dimension to the observing for me.

Many thanks in advance!

[John]

Good questions !

The Veil is one of my favourite deep sky objects to observe. I'd be interested to know more about the science behind it as well

[George Jones]

16 minutes ago, davhei said:

The nebula is approximately 100 ly across however and I did a bit of calculating on the required velocity for the shockwave to reach 50 ly in 8000 years, concluding it would be close to 1900 km/s. Could very well have messed up the numbers though.

Now this seems very high. The sources I found mentioned shockwave speeds of between 40 km/s and 170 km/s. Scientists measuring the speed of the shockwave from supernova remnant W44 came up with 12.9 km/s. 1900 km/s is a far cry from any of these.

Interesting!

I know nothing about the astrophysical processes involved, but, assuming speed is constant, and, using these numbers, I get the same result (see below). 

According to NASA, the shockwave speed is 1.5 million km/h = 420 km/s. If the shockwave is slowing down, this almost seems reasonable.

https://www.spacetelescope.org/news/heic1520/

 

The speed of light is 300000 km/s), so

average speed  = (50 ly/8000y) (300000 km/s) = (1/16) * (300000 km/s) = 1875 km/s

[davhei]

After reading up a bit more, it seems that after the core collapse in the progenitor star, matter can be expelled at velocites close to 0.1 times the speed of light. After hundreds or thousands of years it gradually slows down to the speeds initially mentioned, such as the 40 km/s that purportedly had been measured in the Veil today.

So the changing speed is key, meaning the shockwave covered a lot of distance in the beginning and the slower remainder of it energizes the nebula today, some 50 ly from where it started. Fascinating stuff.

Again, just trying to piece things together in an amateurish way. Please set me right if I’ve gone way off the mark.

[robin_astro]

5 hours ago, davhei said:

After reading up a bit more, it seems that after the core collapse in the progenitor star, matter can be expelled at velocites close to 0.1 times the speed of light.

I routinely measure velocities spectroscopically  over 10^4 km/s from a few days after explosion so yes the initial velocities are high.  Here is an example of my measured velocities.

http://www.spectro-aras.com/forum/viewtopic.php?f=38&t=2308&start=30#p12713

(though in this particular case it is a thermal runaway type Ia supernova rather than a core collapse type II)

Also if we take the crab nebula for example which was a core collapse supernova which exploded 965 years ago, we can measure the current expansion rate directly and spectroscopically to be currently ~ 1000km/s eg

http://spiff.rit.edu/classes/phys231/crab/crab.html

Here is an example of an amateur spectroscopic measurement of the crab nebula expansion rate by Christian Buil et al

http://www.astrosurf.com/buil/us/mission2/mission2.htm

Cheers

Robin

 

Edited August 4, 2019 by robin_astro

[davhei]

Brilliant Robin, thank you!