PDA

View Full Version : How do we know that white dwarfs are Type Ia supernova progenitors?



Tom Mazanec
2012-Feb-27, 11:18 PM
I mean, AFAIK we have never seen a Type Ia before it blew, so how do we know that WDs are what they come from? At least with Type IIs, we have seen some supergiant stars (of all colors, IIRC) explode.

WayneFrancis
2012-Feb-27, 11:27 PM
I thought that it was because the physics is very straight forward which is why they make a very good standard candle. The problems of seeing them first is also that they are a white dwarf and not very luminous to begin with. We might have to detect them by their companion star unless they where very close then we'd have the issue that there is a Super Nova about to go off....very close. So to my laypersons understanding I'm cool with not seeing the progenitors :)

Selfsim
2012-Feb-27, 11:55 PM
I mean, AFAIK we have never seen a Type Ia before it blew, so how do we know that WDs are what they come from? At least with Type IIs, we have seen some supergiant stars (of all colors, IIRC) explode.
You might want to check this out

Earliest-yet observation of August SN2011fe supernova nails it: Destroyed star was white dwarf (http://www.physorg.com/news/2012-01-earliest-yet-august-sn2011fe-supernova-star.html)


A fortuitous observation only four hours after we think the star exploded allowed us to put much more constraining limits on the size of the thing that blew up," said Joshua Bloom, UC Berkeley associate professor of astronomy and first author of a paper interpreting the observation that will appear in the Jan. 10 issue of the Astrophysical Journal Letters.

"The size of the progenitor is so small and the density so high, it pretty much rules out any other reasonable or even fringe possibility. This is a direct confirmation that what blew up is a carbon-oxygen white dwarf."

Hope this helps.

Regards

trinitree88
2012-Feb-28, 01:36 PM
You might want to check this out …

Earliest-yet observation of August SN2011fe supernova nails it: Destroyed star was white dwarf (http://www.physorg.com/news/2012-01-earliest-yet-august-sn2011fe-supernova-star.html)



Hope this helps.

Regards

Notice also that the article mentions that the diameter of the white dwarf's companion is less than a tenth of the sun's, ruling out red giant or main sequence O,B,A,F,G- type stars. That has been the controversy...is it a carbon/oxygen white dwarf and a red supergiant companion (single degenerate model)..or two colliding white dwarves..(double degenerate model)...that fits the bill. The single model held sway for a long time but appears to be incorrect here. SD vs. DD pete

Selfsim
2012-Feb-28, 08:36 PM
And then .. hot off the press (27th Feb, 2012) comes this:

The Merger Rate of Binary White Dwarfs in the Galactic Disk (Badenes & Maoz)
(http://arxiv.org/pdf/1202.5472v1.pdf)
These guys reprocessed 4000 white dwarf spectra (WD) from the SDSS survey, looking for binary WD candidates. They found the princely total of 15, and they say they would've found more, if they were present. Having found these, they then calculated the rate at which these would merge, and then compared that figure with the number of Type 1as seen in distant Milky-Way-looking galaxies.

On average, one double WD merger event happens in the Milky Way about once per century, which happens to be very close to the number of Type 1as observed in galaxies like our own.

They conclude that double WD mergers are thus now, a plausible explanation for Type 1as.

Regards