Author Topic: Supernova Science  (Read 38329 times)

EigenState

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Re: Supernova Science
« Reply #30 on: October 16, 2009, 07:41:17 pm »
Greetings Richard,

I was not faulting Kasen for his presentation at all--just stating my preference for explicitly stated assumptions.  And thanks for sending me more homework.  ;)

You are new here so I should warn you that my reputation is somewhat tarnished here at the forum--too much of a curmudgeon.  :D

Best regards,
ES

Thomas J

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Re: Supernova Science
« Reply #31 on: October 16, 2009, 08:20:58 pm »
This is a very interesting thread. Thanks, Kevin, for thread and thanks and welcome to you, Richard.
I am very interested in the Universe- I am specialising in the Universe and all that surrounds it.....            Peter Cook.


Lovethetropics

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Re: Supernova Science
« Reply #32 on: October 16, 2009, 08:49:23 pm »
Greetings Richard,

I was not faulting Kasen for his presentation at all--just stating my preference for explicitly stated assumptions.  And thanks for sending me more homework.  ;)

You are new here so I should warn you that my reputation is somewhat tarnished here at the forum--too much of a curmudgeon.  :D

Best regards,
ES

Never my dear EigenState, you've been a pillar of sanity for many here. :-*  You're an exemplary zooite even if I don't understand zilch of what you've been talking with Richard.  Math is not my forte, neither is physics.  ;D ;D ;D

 *and find lots of asteroids  ;D

EigenState

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Re: Supernova Science
« Reply #33 on: October 16, 2009, 09:08:29 pm »
Greetings Richard,

I was not faulting Kasen for his presentation at all--just stating my preference for explicitly stated assumptions.  And thanks for sending me more homework.  ;)

You are new here so I should warn you that my reputation is somewhat tarnished here at the forum--too much of a curmudgeon.  :D

Best regards,
ES

Never my dear EigenState, you've been a pillar of sanity for many here. :-*  You're an exemplary zooite even if I don't understand zilch of what you've been talking with Richard.  Math is not my forte, neither is physics.  ;D ;D ;D

My dear Aida,

Thank you, but methinks you are biased in the extreme.  Not that I mind of course.  ;)

Best regards as always,
ES

weezerd

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Re: Supernova Science
« Reply #34 on: October 16, 2009, 09:19:28 pm »
Oi! I overheard that! You do yourself a dis-service my dear ES!
Your contributions and comments have been of great value and cherished in here.
As Aida said, we may well not be able to keep up with you, but that never slowed Einstein or Hawking, so
keep on keeping on!
Oh let me just a moment stay
where time is not and angels play the paeans of the galaxies;
then speed the stardust on its flight
to change dread darkness into light, cold chaos into ecstasy!


Thomas J

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Re: Supernova Science
« Reply #36 on: October 16, 2009, 09:47:36 pm »
I am beginning to sense a conspiracy!  :o
Sense it because I agree with the others above. You are a very helpful and valuable member of the team.  :)
I am very interested in the Universe- I am specialising in the Universe and all that surrounds it.....            Peter Cook.


XYZoo

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Re: Supernova Science
« Reply #37 on: October 17, 2009, 01:25:14 pm »

XYZoo -- Well, I'm not an expert on SN 1987A but I'll try to say something helpful:  Usually the ejected matter from a SN explosion is at first moving very fast (sometimes up to a tenth of the speed of light, 30,000 km/s -- imagine the ticket the police would give you on the highway), so it has a lot of kinetic energy which can be converted into light and heat.  The glowing spots you see are not actually SN ejecta themselves, but gas which had been floating around near the supernova and was heated to very high temperatures after colliding with the SN ejecta.  The reason you see bright spots is because the gas surrounding the SN isn't totally smooth, but is kind of lumpy -- in some places it is denser than others, meaning there's more stuff to heat up and glow.  So parts which are denser than others will appear to glow more brightly in these images.
(...)

Dear Richard,
Thank you very much for taking your precious time to explain these things to me. I got interested in the topic and I am now reading a paper about the geometry of SN1987A, it answers lots of other questions that I had in my mind and prevented me from sleeping  :-\. If anyone else is curious about it, take a look at:
http://arxiv.org/pdf/astro-ph/0502268v1

Richard Scalzo

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Re: Supernova Science
« Reply #38 on: October 17, 2009, 04:00:28 pm »
EigenState -- I have to go with the others here based on what I know so far!  And I appreciate the opportunity to heap homework on you -- it's good to have someone to keep me on my toes and learning cool things too.  :)  There are lots of awesome papers in the literature to which I can point you, so ask away.  ADS is great of course since it has all the citations and references indexed, so it's super easy to follow the paper trail of any line of investigation you please.

XYZoo -- Nice paper!  I don't have time to read it right now but I really hope I can grab some time to take a look at it soon.

cheers,
RS

NGC3314

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Re: Supernova Science
« Reply #39 on: October 23, 2009, 03:54:44 pm »
What assumptions go into the detailed numerical models?  I am thinking chemical composition including relative abundances, temperature assuming LTE, density.  Surely I have missed something.

Caveat - I am not a theorist, a fact pointed out by some professors many years ago. The closest I come on supernova modelling is that I headed a committee that just hired someone who models type Ia explosions. With that said, as I understand it, the modeling process goes roughly as follows:

The initial conditions are taken from a steady-state calculation of the structure of a star just about to explode (silicon-fusing massive star or a white dwarf just edging up on the Chandrasekhar mass limit). That gives the run of temperature, density, and mix of elements with radius in the star. Then one has to follow the energy injection, nucleosynthesis, and dynamics during the explosion (and there are strong hints that this misses important aspects unless it's  done in full 3D simulations). Early in the explosion, energy transport by neutrinos (of all things) can be important. Some of the best algorithms for the nuclear processes are found in the so-called "legacy codes" at Los Alamos. The time and space resolution need to be very fine, since one has to track shock waves, nucleosynthesis, and radiative transfer. Near the surface, the radiative transfer means that the opacity has to be tracked especially finely as a function of wavelength, as does the distribution of where radiation goes from each point since there is scattering and reabsorption to worry about). Then there is the complication of what happens around the newly-collapsed core if it's going to give off a gamma-ray burst. (I have just reminded myself of why I don't do this for a living.)

« Last Edit: October 24, 2009, 06:00:35 pm by NGC3314 »

EigenState

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Re: Supernova Science
« Reply #40 on: October 23, 2009, 06:04:39 pm »
Greetings,

Splendid and thank you!

Is there any possibility that such modeling efforts might lend themselves to a BOINC-like approach to which we volunteers could contribute?

Best regards,
EigenState

Richard Scalzo

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Re: Supernova Science
« Reply #41 on: October 25, 2009, 05:53:46 am »
Hi all,

Sorry I've been inactive lately, I've been working very hard on an exciting SN Ia paper!  I hope to submit it to ApJ within the next week or so, and I'll link the astro-ph listing here once I have one.

cheers,
RS

Lovethetropics

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Re: Supernova Science
« Reply #42 on: October 25, 2009, 06:51:20 am »
That is wonderful Richard!  Congratulations! ;D ;D

 *and find lots of asteroids  ;D

echo-lily-mai

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Re: Supernova Science
« Reply #43 on: October 25, 2009, 07:23:42 pm »
Great news!  ;D

Art does not reproduce the visible....  Paul Klee

Richard Scalzo

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Re: Supernova Science
« Reply #44 on: November 20, 2009, 01:20:26 am »
Dear Zooites,

So unfortunately, the paper hasn't yet been submitted; as my collaborators and I reviewed it we ran into a couple of data analysis snags which are taking a while to iron out.  They won't affect my final result in any major way, but since we plan to release a processed version of the data with the paper for other scientists to play with, it's important that we understand exactly what we are releasing.  A bit disappointing since I'm on the job market this year and want to be able to point to this paper as an example of something awesome I'm doing.  But, due diligence will be done.

The SN I've analyzed looks a lot like SN 2003fg, the one described in

http://www.lbl.gov/Science-Articles/Archive/Phys-weird-supernova.html

which was found by the SNLS collaboration and written up by Andy Howell, one of Zookeeper Mark's American colleagues.  The press release does a good job of describing why the SN is important:  We think the energy which SNe Ia release as visible light comes from radioactive decay, specifically the decay of the isotope nickel-56 into cobalt-56.  SN 2003fg was so bright that it must have produced a very large amount of nickel to begin with.  But the expansion was so slow, given the amount of nickel (based on the brightness), that the assumption was that the white dwarf that exploded to form the SN must have had a very high mass -- so that the gravitational attraction of the total SN mass pulled back on the expanding SN ejecta, decelerating them.  An approximate guess they made was that the white dwarf was around 2 solar masses.

What's weird about this is that nobody knows how to make a 2-solar-mass white dwarf!  The Indian scientist S. Chandrasekhar (after whom the Chandra X-ray Space Telescope is named) calculated back in 1930 that you couldn't make a white dwarf more massive than about 1.4 solar masses, or something catastrophic would happen -- either an explosion or a collapse to a neutron star.  In fact, most people believe SNe Ia result when a white dwarf in a binary system steals enough mass from its companion to put it over the Chandrasekhar limit, thus exploding.  Something like this forces us to re-evaluate how explosions so bright could happen.  What's more, the slow velocity is really hard to understand for a massive white dwarf, since naively, the more fuel you have, the more powerful the explosion will be and the faster the ejecta will be thrown off.  So the brightness is the main piece of evidence that the original white dwarf had to be very massive, and people were keen to figure out how to explain the brightness some other way.

Many people suggested slightly different models in which you had a 1.4-solar-mass white dwarf which was exploding off-center, so that it looked brighter when viewed from the right angle.  But other measurements made by Japanese scientists of the super-bright SN 2009dc showed that it had to be nearly spherical.  So that gets rid of that option, but still doesn't tell us what the right answer is.

What my paper will eventually get around to showing when folks are done with it ;) is, in a nutshell, that these explosions really are that massive.  But it also gives some interesting modeling conclusions for what the progenitor star looked like and how the explosion had to proceed, which should give people a much better handle on how to model these systems.  I'll be able to say more after I submit the paper, but I figured I'd un-stick the discussion first!

Cheers,
Richard