White dwarf mergers

Bikeman (Heinz-Bernd Eggenstein)
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Topic 195229

Hi all!

Recently, some research has shaken the foundations of the previously accepted theory of super nova type Ia explosions: iirc the idea for the main scenario was that a white dwarf in a binary system would accrete matter from the companion star, e.g. a giant star. This would go on until the additional matter reached a certain limit that would ignite a thermonuclear explosion, pretty much ripping the white dwarf into pieces.

New X-ray observations

http://www.nasa.gov/mission_pages/chandra/news/H-10-042.html

show a different picture. A new theory proposes that most of the observed Ia super novae are actually mergers of white dwarfs.

Mergers between two neutron stars have long been studied as sources for gravitational waves.

Are white dwarf - white dwarf mergers fundamentally different as far as GW are concerned? Can we hope to detect the GWs with LIGO or the other detectors directly after a "near" Ia supernova?

CU
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tullio
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White dwarf mergers

We need a supernova in our Galaxy. Last ones were in 1572 (T.Brahe) and 1604 (J.Kepler). To this one Galileo dedicated a story in Padova dialect under a pen name, in order probably to escape the Inquisition. He was teaching in Padova and having a love affair with Marina Gamba. Prof. Enrico Bellone, also of Padova University, published it recently in a book "Galileo e l'abisso. Un racconto", e "Dialogo de Cecco di Ronchitti da Bruzene. In perpuosito de la Stella Nuova". Codice Edizioni, Torino,2009. The "Dialogo" is printed both in Padova dialect and a translation in XVII century Italian by prof.Bellone.
Tullio

Mike Hewson
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RE: Are white dwarf - white

Quote:
Are white dwarf - white dwarf mergers fundamentally different as far as GW are concerned? Can we hope to detect the GWs with LIGO or the other detectors directly after a "near" Ia supernova?


My guess is no ( not radically different compared with BH and NS combo's ), but as white dwarves ( or dwarfs ? ) are lower mass and more variably so I think too, then the energy available for GW production during inspiral/collision is lower than NS or BH. The odds of detection would also depend on the usual lifetime stuff - how many are about, how quickly they evolve, what fraction goes bang in this way etc.

Of additional interest in the article is the mention of a likely significant re-jig of their use as 'standard candles'. That is : they may not be so standard after all, I think they're implying a much wider variability in behaviour with merger vs accretion. So if mergers are the rule then the whole calibration stepladder of universal expansion is in for a real shake up. Hence 'dark' energy et al .....

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Bikeman (Heinz-Bernd Eggenstein)
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RE: We need a supernova in

Message 98864 in response to message 98862

Quote:
We need a supernova in our Galaxy. Last ones were in 1572 (T.Brahe) and 1604 (J.Kepler). To this one Galileo dedicated a story in Padova dialect under a pen name, in order probably to escape the Inquisition. He was teaching in Padova and having a love affair with Marina Gamba. Prof. Enrico Bellone, also of Padova University, published it recently in a book "Galileo e l'abisso. Un racconto", e "Dialogo de Cecco di Ronchitti da Bruzene. In perpuosito de la Stella Nuova". Codice Edizioni, Torino,2009. The "Dialogo" is printed both in Padova dialect and a translation in XVII century Italian by prof.Bellone.
Tullio

I remember reading about those two events recently, they were milestones in astronomy IIRC since Brahe (and his academic heir Kepler) were able to show that the "new star" would not move relative to the "fixed star sphere". AFAIK this shattered the ancient belief that these "novae" or "guest stars" would actually be a phenomenon that took place somewhere between the Earth and the Moon, and was NOT associated to the fixed star sphere which was assumed to be eternal and immutable.

Those were type II (core collapse) super novae, their remnants can still be seen today:

Brahe's nova:

(looks like Pizza Tonno, but you have to imagine it as a 3D structure, easier to see in

Kepler's nova:

)
HB

tullio
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I think I saw a nova (not a

I think I saw a nova (not a supernova) in 1954. It was visible in full daylight. The 1987 supernova in a Magellanic Cloud (don't remember which one) raised a lot of speculations about possible GWs and neutrino observed both under Monte Bianco and at Kamiokande in Japan. Even such an experienced person like Edoardo Amaldi published some of the results obtained in Frascati (GWs) and Monte Bianco tunnel (neutrinos).
Tullio

Bikeman (Heinz-Bernd Eggenstein)
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RE: I think I saw a nova

Message 98866 in response to message 98865

Quote:
I think I saw a nova (not a supernova) in 1954. It was visible in full daylight. The 1987 supernova in a Magellanic Cloud (don't remember which one) raised a lot of speculations about possible GWs and neutrino observed both under Monte Bianco and at Kamiokande in Japan. Even such an experienced person like Edoardo Amaldi published some of the results obtained in Frascati (GWs) and Monte Bianco tunnel (neutrinos).
Tullio

Yeah, SN1987A , in the Large margellanic Cloud.

One of the papers discussing possible (but never really accepted) correlations between GW detector, neutrino detectors and the SN is linked in this discussion.

CU
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Odysseus
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RE: […] white dwarves (

Message 98867 in response to message 98863

Quote:
[…] white dwarves ( or dwarfs ? ) [...]


The normal plural is “dwarfsâ€. “Dwarves†is an archaistic coinage of the fantasy author J.R.R. Tolkien’s (paralleling “wharves†&c.), so should be reserved for that race of beings from his legendarium.

Bikeman (Heinz-Bernd Eggenstein)
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I just found a nice article

I just found a nice article on exactly this topic on the AEI website :

http://www.einstein-online.info/spotlights/galactic-binaries

Looks like this might be something that LISA may catch (even the GW caused by orbital motion, NOT the GW produced by a merger event!):

Quote:
the frequencies are such that the proper instrument to detect them is the Laser Interferometer Space Antenna, LISA, a space-borne gravitational wave detector that might be deployed around 2020.

Hmm...wasn't LISA supposed to be deployed before 2020 ??? Another delay??? "might be deployed" doesn't sound very definitive either :-(.

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tullio
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I just downloaded a

I just downloaded a prepublication copy of a Decadal Survey in Astronomy and Astrophysics by the US National Research Council which lists LISA in third position among large space projects. It should be launched by 2025 in cooperation with ESA.
Tullio

Bikeman (Heinz-Bernd Eggenstein)
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RE: I just downloaded a

Message 98870 in response to message 98869

Quote:
I just downloaded a prepublication copy of a Decadal Survey in Astronomy and Astrophysics by the US National Research Council which lists LISA in third position among large space projects. It should be launched by 2025 in cooperation with ESA.
Tullio

Really, 2025????? It will take some more time (2 yrs?) after launch for the transit to its final orbit, commissioning and calibration before the first science data comes in :-(. This mission get's delayed faster than time progresses, meaning it will never happen if this goes on like this :-(

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tullio
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This book's authors (a who is

This book's authors (a who is who of American astronomy and astrophysics) never heard of BOINC and Einstein@home. Maybe the discovery of one and probably two pulsars by volunteers should open their eyes.
Tullio

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