PDA

View Full Version : Type I supernovae due to planetary impacts?



RGClark
2004-Mar-02, 10:57 AM
From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Type I supernovae due to planetary impacts?
Newsgroups: sci.astro, alt.sci.planetary, sci.physics, sci.geo.geology
Date: 2004-01-08 01:20:37 PST


The news release below discusses observations of a companion star to a
Type I supernova. It mentions that there had been difficulty
confirming the theory that a companion star was necessary for Type I
supernova to occur.
This page also discusses the difficulty in confirming the theory for
Type Ia supernovae:

Source for major type of supernova explosions found
NATIONAL OPTICAL ASTRONOMY OBSERVATORY NEWS RELEASE
Posted: August 6, 2003
"The search for a progenitor for Type Ia supernovae has gone on for so
long that it almost became a point of embarrassment for scientists in
the field," Suntzeff notes. "Supernova 2002ic may not be the prototype
for all Type Ia's, but it is certainly the first crack in the puzzle."
http://spaceflightnow.com/news/n0308/06supernova/

I've been wondering if celestial impacts are common in stellar system
evolution:

From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Re - Strangest Star known is the 'Talk of Astronomy'
Newsgroups: sci.astro, alt.astronomy, sci.physics, alt.fan.art-bell
Date: 2003-09-18 05:27:30 PST
http://groups.google.com/groups?selm=832ea96d.0309180427.27623e75@posting.g oogle.com


Then the explosions seen in Type I supernovae may be due to impacts
of planets to their parent star. This would explain the high amount of
heavy metals seen in such explosions.
In these latest observations of companion stars to the supernovae,
this might be due to the rare cases of planetary systems in binary or
multiple star systems (the rarity being due to gravitational
instability.)

Bob Clark


--------------------------------------------------------------
For email response, send to same userid as above, but append
Hotmail.com instead of Yahoo.com.
--------------------------------------------------------------


************************************************** ***********************
European Space Agency
Science News Release SNR 1-2004
Paris, France 7 January 2004

First supernova companion star found

A joint European/University of Hawaii team of astronomers has for the
first time
observed a stellar 'survivor' to emerge from a double star system
involving an
exploded supernova.

Supernovae are some of the most significant sources of chemical
elements in the
Universe, and they are at the heart of our understanding of the
evolution of
galaxies.

Supernovae are some of the most violent events in the Universe. For
many years
astronomers have thought that they occur in either solitary massive
stars (Type
II supernovae) or in a binary system where the companion star plays an
important
role (Type I supernovae). However no one has been able to observe any
such
companion star. It has even been speculated that the companion stars
might not
survive the actual explosion ...

The second brightest supernova discovered in modern times, SN 1993J,
was found
in the beautiful spiral galaxy M81 on 28 March 1993. From archival
images of
this galaxy taken before the explosion, a red supergiant was
identified as the
mother star in 1993 -- only the second time astronomers have actually
seen the
progenitor of a supernova explosion (the first was SN 1987A, the
supernova that
exploded in 1987 in our neighbouring galaxy, the Large Magellanic
Cloud).

Initially rather ordinary, SN 1993J began to puzzle astronomers as its
ejecta
seemed too rich in the chemical element helium and instead of fading
normally it
showed a bizarre sharp increase in brightness. The astronomers
realised that a
normal red supergiant alone could not have given rise to such a weird
supernova.
It was suggested that the red supergiant orbited a companion star that
had
shredded its outer layers just before the explosion.

Ten years after this cataclysmic event, a European/University of
Hawaii team of
astronomers has now peered deep into the glowing remnants of SN 1993J
using the
NASA/ESA Hubble Space Telescope's Advanced Camera for Surveys (ACS)
and the
giant Keck telescope on Mauna Kea in Hawaii. They have discovered a
massive star
exactly at the position of the supernova that is the long sought
companion to
the supernova progenitor.

This is the first supernova companion star ever to be detected and it
represents
a triumph for the theoretical models. In addition, this observation
allows a
detailed investigation of the stellar physics leading to supernova
explosions.
It is now clear that during the last 250 years before the explosion 10
solar
masses of gas were torn violently from the red supergiant by its
partner. By
observing the companion closely in the coming years it may even be
possible to
detect a neutron star or black hole emerge from the remnants of the
explosion
'in real time'.

Given the paucity of observations of supernova progenitor systems this
result,
published in Nature on 8 January 2004, is likely to "be crucial to
understanding
how very massive stars explode and why we see such peculiar
supernovae"
according to first author Justyn R. Maund from the University of
Cambridge, UK.

Stephen Smartt, also from the University of Cambridge, says:
"Supernova
explosions are at the heart of our understanding of the evolution of
galaxies
and the formation of chemical elements in the Universe. It is
essential that we
know what type of stars produce them." For the last ten years
astronomers have
believed that they could understand the very peculiar behaviour of
1993J by
invoking the existence of a binary companion star and now this picture
has
proved correct.

According to Rolf Kudritzki from the University of Hawaii, "The
combination of
the outstanding spatial resolution of Hubble and the huge light
gathering power
of the Keck 10m telescope in Hawaii has made this fantastic discovery
possible."

Supernovae occur when a star of more than about eight times the mass
of the Sun
reaches the end of its nuclear fuel reserves and can no longer produce
enough
energy to keep the star from collapsing under its own immense weight.
The core
of the star collapses, and the outer layers are ejected in a
fast-moving shock
wave. This huge energy release causes the visible supernova we see.
While
astronomers are convinced that observations will match this
theoretical model,
they are in the embarrassing position that they have confidently
identified only
two stars that later exploded as supernovae -- the precursors of
supernovae
1987A and 1993J.

There have been more than 2000 supernovae discovered in galaxies
beyond the
Milky Way and there appear to be about eight distinct sub-classes.
However
identifying which stars produce which flavours has proved incredibly
difficult.
This team has now embarked on a parallel project with the Hubble Space
Telescope
to image a large number of galaxies and then wait patiently for a
supernova to
explode. Supernovae appear in spiral galaxies like M81 on average once
every 100
years or so. The team, led by Stephen Smartt, hope to increase the
numbers of
supernova progenitors known from 2 to 20 over the next five years.

Notes for editors

The team is composed of Stephen J. Smartt and Justyn R. Maund
(University of
Cambridge, UK), Rolf. P. Kudritzki (University of Hawaii, USA),
Philipp
Podsiadlowski (University of Oxford, UK) and Gerry F. Gilmore
(University of
Cambridge, UK).

Animations of the discovery and general Hubble Space Telescope
background
footage are available from
http://www.spacetelescope.org/video/heic0401_vnr.html

For more information, please contact:

Justyn R. Maund
University of Cambridge
Tel: +44 (0)1223 337544
E-mail: jrm@ast.cam.ac.uk

Stephen Smartt
University of Cambridge
Tel: +44 (0)1223 766 651
E-mail: sjs@ast.cam.ac.uk

Rolf. P. Kudritzki
Institute for Astronomy
University of Hawaii
Tel: +1 808 956 8566
E-mail: kud@ifa.hawaii.edu

Lars Lindberg Christensen
Hubble European Space Agency Information Centre
Garching, Germany
Tel: +49 89 3200 6306 (089 within Germany)
E-mail: lars@eso.org

[NOTE: Images supporting this release are available at
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=34455 ]


************************************************** ***********************

Spaceman Spiff
2004-Mar-02, 06:43 PM
And why would he (or you) suspect that a star would explode, merely because a planet "fell into it"? If two normal stars merged (an extremely rare event), they would not explode.

Let's do the experiment: drop a Jupiter into the Sun from a great distance away.

released gravitational potential energy:
G M_Sun * M_Jup/R_Sun = 3.6e45 ergs

The Sun's gravitational binding energy is roughly:
G * (M_sun)^2/R_sun = 3.8e48 ergs, or surprise, surprise, a factor of M_sun/M_jupiter = 1047x larger. The sun goes "burp! thank you."

But as I said above, even the merging of two normal stars does not an exploding star make.

Kaptain K
2004-Mar-02, 07:32 PM
There was an article in Scientific American sometime last year on the consequences of various mergers/collisions. IIRC, the only scenario that resulted in complete destruction of the Sun was a neutron star! :o

RGClark
2004-Mar-05, 04:14 PM
Thanks for the ref. in SciAm, Kaptain K. I'll look that up.


Bob Clark

RGClark
2004-Mar-05, 04:35 PM
And why would he (or you) suspect that a star would explode, merely because a planet "fell into it"? If two normal stars merged (an extremely rare event), they would not explode.

Let's do the experiment: drop a Jupiter into the Sun from a great distance away.

released gravitational potential energy:
G M_Sun * M_Jup/R_Sun = 3.6e45 ergs

The Sun's gravitational binding energy is roughly:
G * (M_sun)^2/R_sun = 3.8e48 ergs, or surprise, surprise, a factor of M_sun/M_jupiter = 1047x larger. The sun goes "burp! thank you."

But as I said above, even the merging of two normal stars does not an exploding star make.

In neither Type I nor Type II supernovae does the star entirely explode, there is always a remnant. Most importantly note the theory for Type I supernovae is for white dwarfs which are typically 1/100th the Sun's radius.
The result is quite a HUGE explosion.
This is not a merger. I'm visioning a direct impact of one body into another. BTW, calculate the velocity of the body impacting at the white dwarf radius. I think you'll be surprised.

Bob Clark

Spaceman Spiff
2004-Mar-05, 07:42 PM
And why would he (or you) suspect that a star would explode, merely because a planet "fell into it"? If two normal stars merged (an extremely rare event), they would not explode.

Let's do the experiment: drop a Jupiter into the Sun from a great distance away.

released gravitational potential energy:
G M_Sun * M_Jup/R_Sun = 3.6e45 ergs

The Sun's gravitational binding energy is roughly:
G * (M_sun)^2/R_sun = 3.8e48 ergs, or surprise, surprise, a factor of M_sun/M_jupiter = 1047x larger. The sun goes "burp! thank you."

But as I said above, even the merging of two normal stars does not an exploding star make.

In neither Type I nor Type II supernovae does the star entirely explode, there is always a remnant. Most importantly note the theory for Type I supernovae is for white dwarfs which are typically 1/100th the Sun's radius.
The result is quite a HUGE explosion.
This is not a merger. I'm visioning a direct impact of one body into another. BTW, calculate the velocity of the body impacting at the white dwarf radius. I think you'll be surprised.

Bob Clark

Ok, so you want to drop a Jupiter (starting from large distance) onto a white dwarf of, say, 1 solar mass?

released gravitational potential energy:
G M_Sun * M_Jup/R_wd = 4 x 10^47 ergs

LUMINOUS energy released from Type 1a SN: ~10^51 ergs.

Hey, don't get me wrong. I wouldn't want to be standing around anywhere near such an event, but this still is a far cry from a Type 1a SN. And how would a planet find itself falling upon white dwarf?

RGClark
2004-Mar-06, 02:36 AM
Ok, so you want to drop a Jupiter (starting from large distance) onto a white dwarf of, say, 1 solar mass?

released gravitational potential energy:
G M_Sun * M_Jup/R_wd = 4 x 10^47 ergs

LUMINOUS energy released from Type 1a SN: ~10^51 ergs.

Hey, don't get me wrong. I wouldn't want to be standing around anywhere near such an event, but this still is a far cry from a Type 1a SN. And how would a planet find itself falling upon white dwarf?

Calculate for me if you will what the impacting speed will be at 1/100th of a Solar radius or better yet at a 1/1000th Solar radius.
I think you'll get an idea where the extra energy will come from.


Bob Clark

JohnOwens
2004-Mar-06, 02:59 AM
Ok, so you want to drop a Jupiter (starting from large distance) onto a white dwarf of, say, 1 solar mass?

released gravitational potential energy:
G M_Sun * M_Jup/R_wd = 4 x 10^47 ergs

LUMINOUS energy released from Type 1a SN: ~10^51 ergs.

Hey, don't get me wrong. I wouldn't want to be standing around anywhere near such an event, but this still is a far cry from a Type 1a SN. And how would a planet find itself falling upon white dwarf?

Calculate for me if you will what the impacting speed will be at 1/100th of a Solar radius or better yet at a 1/1000th Solar radius.
I think you'll get an idea where the extra energy will come from.

Looks to me like he just did figure it using 1/100th R_Sol. Assuming the basic formula is correct (I'm not going to bother checking right now), using 1/1000 R_Sol would just make it around 4 x 10^48 ergs. I haven't checked the math myself either, but that should be evident from the earlier 3.6 x 10^45 ergs for a full R_Sol radius, and the inverse relationship in the formula for the energy and the radius. 1/100 R_Sol gives 100 times as much energy, 1/1000 R_Sol gives 1000 times as much. And I figure he just rounded from 3.6 x 10^47 to 4 x 10^47.

RGClark
2004-Mar-06, 03:22 PM
Looks to me like he just did figure it using 1/100th R_Sol. Assuming the basic formula is correct (I'm not going to bother checking right now), using 1/1000 R_Sol would just make it around 4 x 10^48 ergs. I haven't checked the math myself either, but that should be evident from the earlier 3.6 x 10^45 ergs for a full R_Sol radius, and the inverse relationship in the formula for the energy and the radius. 1/100 R_Sol gives 100 times as much energy, 1/1000 R_Sol gives 1000 times as much. And I figure he just rounded from 3.6 x 10^47 to 4 x 10^47.

Thanks for the response. But I wanted to make a particular point about the VERY high speeds that will be achieved at impact by this massive planetary body.
To calculate it, set the kinetic energy equal to the potential energy. You get this equation:

mV^2/2 = GMm/R

So V = sqrt(2GM/R), with M the star mass, m the planet mass, R the radial distance, and G the gravitational constant, G = 6.67 x 10^(-11)m^3/s^2 x kg.
Try it for R at 1/100th the solar radius and for R at 1/1000th the solar radius.
I think you'll find it interesting.


Bob Clark

Spaceman Spiff
2004-Mar-06, 09:32 PM
Looks to me like he just did figure it using 1/100th R_Sol. Assuming the basic formula is correct (I'm not going to bother checking right now), using 1/1000 R_Sol would just make it around 4 x 10^48 ergs. I haven't checked the math myself either, but that should be evident from the earlier 3.6 x 10^45 ergs for a full R_Sol radius, and the inverse relationship in the formula for the energy and the radius. 1/100 R_Sol gives 100 times as much energy, 1/1000 R_Sol gives 1000 times as much. And I figure he just rounded from 3.6 x 10^47 to 4 x 10^47.

Thanks for the response. But I wanted to make a particular point about the VERY high speeds that will be achieved at impact by this massive planetary body.
To calculate it, set the kinetic energy equal to the potential energy. You get this equation:

mV^2/2 = GMm/R

So V = sqrt(2GM/R), with M the star mass, m the planet mass, R the radial distance, and G the gravitational constant, G = 6.67 x 10^(-11)m^3/s^2 x kg.
Try it for R at 1/100th the solar radius and for R at 1/1000th the solar radius.
I think you'll find it interesting.


Bob Clark

For such a collision of a Jupiter with a WD, I get about 6000 km/s, in the newtonian limit (we're a tad relativistic). So your point is? This doesn't correspond to anywhere near the luminous energy of a SN, as I stated above.

And yeah, if you drop a planet on to a neutron star you reach relativistic type energies. But this is no surprise. The question is why should planets fall on to a WD or neutron star? And why should this be any reasonable explanation for Type Ia supernovae? Do you know what spectrum of light would come from such an event, and how such would evolve in time? Because astronomers measure these, and as such are tests of any hypothesis.

RGClark
2004-Mar-06, 11:20 PM
For such a collision of a Jupiter with a WD, I get about 6000 km/s, in the newtonian limit (we're a tad relativistic). So your point is? This doesn't correspond to anywhere near the luminous energy of a SN, as I stated above.

And yeah, if you drop a planet on to a neutron star you reach relativistic type energies. But this is no surprise. The question is why should planets fall on to a WD or neutron star? And why should this be any reasonable explanation for Type Ia supernovae? Do you know what spectrum of light would come from such an event, and how such would evolve in time? Because astronomers measure these, and as such are tests of any hypothesis.

6000 km/sec is an extraordinary speed for a massive body to be moving at on impact to another body. We are used to seeing small subatomic particles moving at significant fractions of the speed of light but this a Jupiter size mass hitting the star all at once at that speed.
Now think of a fission bomb. It requires high speed of the radioactive materials to achieve fission, requiring high explosives to attain. But of course these are moving at nowhere near 6000 km/sec! I'm suggesting that even Jovian size planets will contain fissionable elements in their solid cores and these high speeds with their induced compressions will induce atomic fission at least.
In fact these relativistic speeds may even be sufficient to induce fusion with the hydrogen/helium in the star and planet.
As to why the planets would impact the star, there has been both observational and theoretical evidence to suggest close-in Jovian planets, 'hot' Jupiters, eventually impact their primaries:

Exploring New Worlds
Scientists puzzle over extrasolar planets
Science News, August 8, 1998
http://sciencenews.org/sn_arc98/8_8_98/bob1.htm

Stars May Be Eating 'Hot Jupiters'
http://www.space.com/scienceastronomy/astronomy/stars_planets_991022.html



Bob Clark

Kaptain K
2004-Mar-07, 12:40 AM
As to why the planets would impact the star, there has been both observational and theoretical evidence to suggest close-in Jovian planets, 'hot' Jupiters, eventually impact their primaries
No, they don't impact the primary. They are in orbit. When the orbit decays to the point where they reach Roche's Limit, they are tidally shredded and the remains form an accretion disk around the primary. From there, the process is the same as with with the white dwarf siphoning material from a companion star. If there is sufficient material, there will be a Type Ia supernova indistinguishable from one caused by accretion from a companion star.

Manchurian Taikonaut
2004-Mar-07, 08:55 AM
heres a good image of super nova remnant LCM N 49


http://imgsrc.hubblesite.org/hu/db/2003/20/images/a/formats/web.jpg

taken by NASAs hubble

tracer
2004-Mar-07, 04:05 PM
Ok, so you want to drop a Jupiter (starting from large distance) onto a white dwarf of, say, 1 solar mass?

released gravitational potential energy:
G M_Sun * M_Jup/R_wd = 4 x 10^47 ergs

LUMINOUS energy released from Type 1a SN: ~10^51 ergs.

Hey, don't get me wrong. I wouldn't want to be standing around anywhere near such an event, but this still is a far cry from a Type 1a SN.
*cough* Chandrasekhar Limit *cough* neutron star formation *cough*

Spaceman Spiff
2004-Mar-07, 05:43 PM
For such a collision of a Jupiter with a WD, I get about 6000 km/s, in the newtonian limit (we're a tad relativistic). So your point is? This doesn't correspond to anywhere near the luminous energy of a SN, as I stated above.

And yeah, if you drop a planet on to a neutron star you reach relativistic type energies. But this is no surprise. The question is why should planets fall on to a WD or neutron star? And why should this be any reasonable explanation for Type Ia supernovae? Do you know what spectrum of light would come from such an event, and how such would evolve in time? Because astronomers measure these, and as such are tests of any hypothesis.

6000 km/sec is an extraordinary speed for a massive body to be moving at on impact to another body. We are used to seeing small subatomic particles moving at significant fractions of the speed of light but this a Jupiter size mass hitting the star all at once at that speed.
Now think of a fission bomb. It requires high speed of the radioactive materials to achieve fission, requiring high explosives to attain. But of course these are moving at nowhere near 6000 km/sec! I'm suggesting that even Jovian size planets will contain fissionable elements in their solid cores and these high speeds with their induced compressions will induce atomic fission at least.
In fact these relativistic speeds may even be sufficient to induce fusion with the hydrogen/helium in the star and planet.
As to why the planets would impact the star, there has been both observational and theoretical evidence to suggest close-in Jovian planets, 'hot' Jupiters, eventually impact their primaries:

Exploring New Worlds
Scientists puzzle over extrasolar planets
Science News, August 8, 1998
http://sciencenews.org/sn_arc98/8_8_98/bob1.htm

Stars May Be Eating 'Hot Jupiters'
http://www.space.com/scienceastronomy/astronomy/stars_planets_991022.html



Bob Clark

To take care of a detail, I've assumed, and so has RGClark, that the planet fell into the star from effective infinity (or d >> R_*). If the planet "fell" in from a last stable orbit, this speed would be approximately sqrt(2) or so smaller. (i.e., the energy about a factor of 2 or so less).

However, as stated above by myself and others, planets don't just fall in whole into a star. They have some angular momentum, unless some mechanism removes it. If their orbit takes them inside the tidal radius of the star, the planet will be distorted and then broken apart. Some or most of that mass may never impact the star. If you're going to drop in a Jovian's mass of material, somehow you've got to remove its angular momentum.

Next, these Jovians whose orbits migrate inward are expected to do so early on in that solar system's history in the presence of the original accretion disk (which acts as a mechanism for removing orbital energy and angular momentum). The presence of a white dwarf means that the system has been present for approximately 1 billion years. If the star had Jovians, and if they were to migrate inward, they would have done so long ago.

As for pushing the WD over the Chandrasekhar limit (1.4 solar masses) by dropping in a planet....I remind everyone that the mass of Jupiter is 1/1047 the mass of the sun. So how many planets are you going to drop in?

Nevertheless, if one were to somehow drop a jupiter onto a WD, conditions might be proper for fusion to occur at the surface of the WD. In this case, then at best you might get 0.7% of the rest mass of the Jovian converted into luminous energy. This energy would be appreciable, perhaps 10^49 ergs.

However, a star overfilling its Roche Lobe in a close binary system with a WD is known to "dump" similar amounts of material, and the result is either called a nova or a Type 1a supernova, depending upon the energy involved in the resultant thermonuclear runaway that occurs on the WD surface or within its interior, respectively. There are a whole category of stars called Cataclysmic Variables that are KNOWN to be in this configuration. Ditto for X-ray binaries, in which a neutron star occurs in a tight orbit with a normal star overfilling its Roche Lobe. So why do we need to drop Jovians onto WD and NS?

tracer
2004-Mar-08, 02:15 AM
As for pushing the WD over the Chandrasekhar limit (1.4 solar masses) by dropping in a planet....I remind everyone that the mass of Jupiter is 1/1047 the mass of the sun. So how many planets are you going to drop in?
If the WD is currently at 1.399 solar masses, it's only gonna take one.

Spaceman Spiff
2004-Mar-08, 02:32 PM
As for pushing the WD over the Chandrasekhar limit (1.4 solar masses) by dropping in a planet....I remind everyone that the mass of Jupiter is 1/1047 the mass of the sun. So how many planets are you going to drop in?
If the WD is currently at 1.399 solar masses, it's only gonna take one.

That doesn't happen very often. In fact the vast majority of WDs are less massive than our Sun.

Spaceman Spiff
2004-Mar-08, 03:02 PM
This is just a follow-up on my post above (http://www.badastronomy.com/phpBB/viewtopic.php?p=219370#219370).

The estimate I gave for the possible energy released in fusion should a Jovian planet and a WD collide really was an upper limit, and not very likely.
Assumptions:
1) 0.7% efficiency in converting matter into energy
2) all of the planet's mass was available to fuse

#1 above only holds for the conversion of H into Helium. All other processes are less than 1/10th as efficient.

#2 is unlikely, even IF the WD were to somehow capture the full Jovian's mass. If fusion were to occur, then as soon as it began in earnest, the energy released would likely blow off the Jovian envelope before the remainder of the mass could undergo fusion. It is conceivable that such a process would be repeated using the material that wasn't blasted to escape velocity.

Even in normal novae it is known that only about a third of the material dumped onto the surface of the WD, via accretion of gas from the secondary star overfilling its Roche Lobe, participates in the hydrogen fusion that ultimately results. The rest is blown off.

In Type 1a supernovae, a substantial fraction of the WD's mass undergoes fusion; this why they are so luminous. The C/O in the WD's central regions may reach sufficient temperatures for C fusion if the WD's mass exceeds 1.3 solar masses. Because the electrons are degenerate, energy released from fusion may run away (lack a pressure/temperature thermostat) to exceed the binding energy of the WD.

But the bottom line is, dumping a Jovian onto a WD is no easy task, and therefore highly unlikely. Stars are found in binary systems. We know of WD's and normal stars as such pairs. We know of such pairs where the normal star has filled its Roche Lobe and is dumping mass, via an accretion disk, onto the WD. The gas viscosity in the disk is the mechanism for removing angular momentum, allowing the gas to eventually fall onto the WD. Thermal energy from the viscous disk is carried away as light.
Depending upon how this mass transfer rate occurs and the mass of the WD, we get wide ranging types of novae, plus -- apparently -- the opporturnity to produce a Type 1a SN that disrupts the entire WD.

RGClark
2004-Mar-09, 12:04 AM
...

But the bottom line is, dumping a Jovian onto a WD is no easy task, and therefore highly unlikely. Stars are found in binary systems. We know of WD's and normal stars as such pairs. We know of such pairs where the normal star has filled its Roche Lobe and is dumping mass, via an accretion disk, onto the WD. The gas viscosity in the disk is the mechanism for removing angular momentum, allowing the gas to eventually fall onto the WD. Thermal energy from the viscous disk is carried away as light.
Depending upon how this mass transfer rate occurs and the mass of the WD, we get wide ranging types of novae, plus -- apparently -- the opporturnity to produce a Type 1a SN that disrupts the entire WD.

A key problem with the standard explanation of the Type 1a supernovae is that the required companion star is so hard to spot. It is true that binary systems are common. Yet with these supernovae, these companions can not be found except perhaps for the one or two in these press releases.
Note this would make sense if these supernovae occurred in systems with planets since stable planetary systems are easier to form in single stellar systems because of the gravitaional instability caused by multiple stars.


Bob Clark

tracer
2004-Mar-09, 06:23 AM
Okay, consider this scenario:

Star a couple of times the size of the sun dies, and leaves behind a white dwarf. After shedding its outer layers as a so-called planetary nebula, the white dwarf is on the high end masswise, at about 1.2 or 1.3 solar masses.

Of course, this star isn't standing out there all by its lonesome. It's got some planets and asteroids orbiting it, perhaps even a "hot jupiter" or two like 51 Pegasi has. It's also got a huge extended Oort-cloud-like halo of comets extending out to half a light-year or so.

Now, up until the time the star dies, all of these objects have been in more-or-less stable orbits. But now, all of a sudden, they've got this huge expanding planetary nebula wafting through their midst. This gas, although extremely rarefied, will induce some amount of drag on all these objects orbiting the dead star. For objects like Oort-cloud comets, which are all in extremely eccentric orbits and spend most of their millennia at or near apastron, this tiny amount of drag is going to reduce their velocity while they're at or near apastron.

And what happens to an object at apastron that loses velocity? Its periastron distance becomes shorter. Now all these comets that used to keep a safe distance from the star they were orbiting find themselves skirting dangerously close to this newly-formed white dwarf in the center of the star system. So close, in fact, that many many many of them are bound to spiral in to it.

The mass of an entire Oort cloud full of comets has got to far exceed the piddling little couple of Jupiter masses inside the star's regular planetary system. It is this mass, not the mass of one or two Jovian planets, that falls onto the white dwarf, pushes it up past the Chandrasekhar Limit, and gives us a Type I Supernova.

Kaptain K
2004-Mar-09, 08:22 AM
The best estimate of the total mass of the Sun's Oort cloud is sgnificantly less than one Jovian mass.

Spaceman Spiff
2004-Mar-09, 04:14 PM
The best estimate of the total mass of the Sun's Oort cloud is sgnificantly less than one Jovian mass.

Yes, the current estimates are in the range of several Earths, though this remains under investigation with a large uncertainty.

Spaceman Spiff
2004-Mar-09, 04:24 PM
Okay, consider this scenario:

Star a couple of times the size of the sun dies, and leaves behind a white dwarf. After shedding its outer layers as a so-called planetary nebula, the white dwarf is on the high end masswise, at about 1.2 or 1.3 solar masses.

Of course, this star isn't standing out there all by its lonesome. It's got some planets and asteroids orbiting it, perhaps even a "hot jupiter" or two like 51 Pegasi has. It's also got a huge extended Oort-cloud-like halo of comets extending out to half a light-year or so.

Now, up until the time the star dies, all of these objects have been in more-or-less stable orbits. But now, all of a sudden, they've got this huge expanding planetary nebula wafting through their midst. This gas, although extremely rarefied, will induce some amount of drag on all these objects orbiting the dead star. For objects like Oort-cloud comets, which are all in extremely eccentric orbits and spend most of their millennia at or near apastron, this tiny amount of drag is going to reduce their velocity while they're at or near apastron.

And what happens to an object at apastron that loses velocity? Its periastron distance becomes shorter. Now all these comets that used to keep a safe distance from the star they were orbiting find themselves skirting dangerously close to this newly-formed white dwarf in the center of the star system. So close, in fact, that many many many of them are bound to spiral in to it.

The mass of an entire Oort cloud full of comets has got to far exceed the piddling little couple of Jupiter masses inside the star's regular planetary system. It is this mass, not the mass of one or two Jovian planets, that falls onto the white dwarf, pushes it up past the Chandrasekhar Limit, and gives us a Type I Supernova.

Interesting scenario.
Can you point me to a peer-reviewed paper that reports such numerical simulations?
Is this enough time for such rarefied gas involved in the slow and fast wind (envelope ejection) episodes to impart significant drag? Keep in mind, too, that as the star's former envelope "wafts past" the comets they feel an increasingly smaller interior mass. I'd have to see a numerical simulation.

RGClark
2004-Mar-09, 05:53 PM
...Nevertheless, if one were to somehow drop a jupiter onto a WD, conditions might be proper for fusion to occur at the surface of the WD. In this case, then at best you might get 0.7% of the rest mass of the Jovian converted into luminous energy. This energy would be appreciable, perhaps 10^49 ergs.
...


Where do you get the .7% figure from? Are you assuming only one specific type of nuclear reaction?

This post from Tracer under the thread "The Sun as a hydrogen bomb" indicates there are nuclear fusion reactions resulting in 1/4 of a star's core mass being consumed:


tracer
Bad Master
Joined: 17 Dec 2002
Posts: 1567
Location: Silicon Valley, CA, USA
Posted: Tue Mar 09, 2004 3:47 pm** *Post subject:
------------------------------------------------------------------------
Even if all the hydrogen in the sun's core were deuterium, I don't know if it would "explode."

Consider the Helium Flash: The core of a red giant is about half-and-half hydrogen and Helium-4 in the same kind of electron-degenerate state ao a white dwarf. When the hydrogen-burning shell around the core raisies its temperature to a critical level, about half the Helium-4 in the core -- in other words, 1/4 of the core's entire mass -- all spontaneously undergoes thermonuclear fusion into Carbon-12 in a matter of seconds.



Bob Clark

Spaceman Spiff
2004-Mar-09, 06:36 PM
...Nevertheless, if one were to somehow drop a jupiter onto a WD, conditions might be proper for fusion to occur at the surface of the WD. In this case, then at best you might get 0.7% of the rest mass of the Jovian converted into luminous energy. This energy would be appreciable, perhaps 10^49 ergs.
...


Where do you get the .7% figure from? Are you assuming only one specific type of nuclear reaction?

This post from Tracer under the thread "The Sun as a hydrogen bomb" indicates there are nuclear fusion reactions resulting in 1/4 of a star's core mass being consumed:


tracer
Bad Master
Joined: 17 Dec 2002
Posts: 1567
Location: Silicon Valley, CA, USA
Posted: Tue Mar 09, 2004 3:47 pm** *Post subject:
------------------------------------------------------------------------
Even if all the hydrogen in the sun's core were deuterium, I don't know if it would "explode."

Consider the Helium Flash: The core of a red giant is about half-and-half hydrogen and Helium-4 in the same kind of electron-degenerate state ao a white dwarf. When the hydrogen-burning shell around the core raisies its temperature to a critical level, about half the Helium-4 in the core -- in other words, 1/4 of the core's entire mass -- all spontaneously undergoes thermonuclear fusion into Carbon-12 in a matter of seconds.



Bob Clark

Tracer was describing the amount of mass undergoing fusion. I was describing the amount of mass converted into energy. All one does is compare the mass of the net reactants to the mass of the net products. The difference, if positive, is the energy released into the environment.

In converting hydrogen into helium, just under 0.7% of the hydrogen undergoing fusion is converted into energy, and most of that would be luminous energy. In converting helium into carbon (and then oxygen), the efficiency is about 10x smaller. It's even smaller the closer you get to iron.

tracer
2004-Mar-09, 08:40 PM
Can you point me to a peer-reviewed paper that reports such numerical simulations?
Is this enough time for such rarefied gas involved in the slow and fast wind (envelope ejection) episodes to impart significant drag? Keep in mind, too, that as the star's former envelope "wafts past" the comets they feel an increasingly smaller interior mass. I'd have to see a numerical simulation.
Hmph! Party pooper.

Tom Mazanec
2009-Feb-03, 06:23 PM
"The team, led by Stephen Smartt, hope to increase the
numbers of
supernova progenitors known from 2 to 20 over the next five years."
It is about five years since this was written.
Anyone have stats on known progenitors?

timb
2009-Feb-03, 10:35 PM
In neither Type I nor Type II supernovae does the star entirely explode, there is always a remnant.


In a type Ia supernova the white dwarf is completely unbound.

Hornblower
2009-Feb-05, 12:09 AM
Now think of a fission bomb. It requires high speed of the radioactive materials to achieve fission, requiring high explosives to attain.

No speed is required to achieve fission, which is caused by capture of neutrons by fissile uranium or plutonium nuclei. We could build up a critical mass of the stuff at a snail's pace, and enough neutrons would be captured to get a sustained chain reaction going.

The purpose of the high explosive detonator action is to abruptly transform the main charge from a subcritical storage configuration to a supercritical form in which a runaway chain reaction builds up quickly, and to hold it together long enough for the reaction to consume the main charge before it flies apart.

Jerry
2009-Feb-06, 07:19 PM
The dirth of supernova progenitors is surprising. Type Ia more-or-less universally show evidence of polarization in the light curves. So a collisional mechanism has to be considered a possibility: This runs counter to our expected dynamics for stars, but given the high number of binary systems we do see; the probability of binaries hurling their partners into a system they would otherwise orbit increases.

Jerry
2009-Feb-18, 04:29 AM
http://lanl.arxiv.org/abs/0902.2794v1

An Extremely Low Luminosity and Extremely Low Energy Supernova
Foley et al

Subluminous, but with the spectral signature of a type Ia

It is easy to differentiate, because of the low expansion velocity; but it also tells us you don't have to reach a critical mass to trigger a type Ia spectral event.

The expanding range of possible luminousities devalues the use of 'type Ia' as standard candles; especially the optomistic practice of using 'type Ia' at cosmic distances to determine whether or not the universe is expanding. (It would only take a slight contamination of events not quite this peculiar to skew the results towards accelerated expansion.)