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The expanding shell  around V445 Puppis.  Credit:  ESO

Astronomers Find Type Ia Supernova Just Waiting to Happen

17 Nov , 2009

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Type Ia supernovae are a mystery because no one can predict when or where one might occur. But astronomers are hedging their bets on V445 Puppis. A so-called “vampire white dwarf” that underwent a nova outburst after gulping down part of its companion’s matter in 2000, now, it appears this double star system is a prime candidate for exploding. “Whether V445 Puppis will eventually explode as a supernova, or if the current nova outburst has pre-empted that pathway by ejecting too much matter back into space is still unclear,” said Patrick Woudt, from the University of Cape Town and lead author of the paper reporting the results. “But we have here a pretty good suspect for a future Type Ia supernova!”

This is the first, and so far only nova showing no evidence at all for hydrogen, and provides the first evidence for an outburst on the surface of a white dwarf dominated by helium. “This is critical, as we know that Type Ia supernovae lack hydrogen,” said Danny Steeghs, from the University of Warwick, UK, “and the companion star in V445 Pup fits this nicely by also lacking hydrogen, instead dumping mainly helium gas onto the white dwarf.”

Click here to watch a movie of the expanding shell of V445 Puppis.

The astronomers have determined the system is about 25,000 light-years from the Sun, and it has an intrinsic brightness of over 10,000 times our Sun. This implies that the vampire white dwarf in this system has a high mass that is near its fatal limit and is still simultaneously being fed by its companion at a high rate.

“One of the major problems in modern astrophysics is the fact that we still do not know exactly what kinds of stellar system explode as a Type Ia supernova,” said Woudt, “As these supernovae play a crucial role in showing that the Universe’s expansion is currently accelerating, pushed by a mysterious dark energy, it is rather embarrassing.”

Shell around V445 Puppis  (March 2005). Credit: ESO

Shell around V445 Puppis (March 2005). Credit: ESO


Woudt and his team used the ESO’s Very Large Telescope (VLT) to obtain very sharp images of V445 Puppis over a time span of two years. The images show a bipolar shell, initially with a very narrow waist, with lobes on each side. Two knots are also seen at both the extreme ends of the shell, which appear to move at about 30 million kilometers per hour. The shell — unlike any previously observed for a nova — is itself moving at about 24 million kilometers per hour. A thick disc of dust, which must have been produced during the last outburst, obscures the two central stars.

As Steeghs said, one defining characteristic of Type Ia supernovae is the lack of hydrogen in their spectrum. Yet hydrogen is the most common chemical element in the Universe. Such supernovae most likely arise in systems composed of two stars, one of them being the end product of the life of sun-like stars, or white dwarfs. When such white dwarfs, acting as stellar vampires that suck matter from their companion, become heavier than a given limit, they become unstable and explode.

The build-up is not a simple process. As the white dwarf cannibalizes its prey, matter accumulates on its surface. If this layer becomes too dense, it becomes unstable and erupts as a nova. These controlled, mini-explosions eject part of the accumulated matter back into space. The crucial question is thus to know whether the white dwarf can manage to gain weight despite the outburst, that is, if some of the matter taken from the companion stays on the white dwarf, so that it will eventually become heavy enough to explode as a supernova.

Read the team’s paper.

Source: ESO

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Dave Finton
Member
November 17, 2009 9:21 AM

I wonder if a star going nova really does apply for the title “mini-explosion” =D

Lawrence B. Crowell
Member
Lawrence B. Crowell
November 17, 2009 10:31 AM

If this does explode it might give us better estimates on the use of SNIs as a cosmic standard candle.

LC

ND
Member
ND
November 17, 2009 11:52 AM

A space kablooee. Can’t wait!

Anaconda
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Anaconda
November 17, 2009 12:31 PM

Curious that a star exploding has the same hourglass shape as a star forming.

How does the accepted model explain that?

DrFlimmer
Member
DrFlimmer
November 17, 2009 2:42 PM
Quoting from BA (about the same topic): The debris did not expand spherically because the two stars are in a tight orbit, circling each other rapidly. The matter drawn off the normal star forms a thick disk around the white dwarf. When the material on the surface exploded, it couldn’t go through the disk, so it went up and down, above and below the disk. Over time it forms what’s called a bipolar structure, because it comes out of the poles of the star. We see lots of similar bipolar objects, but not usually in a system that’s about to go bye-bye. Someone over at BA also said that it would be visible for a VERY long period… Read more »
ND
Member
ND
November 17, 2009 3:05 PM

DrFlimmer,

We need some telescopes trained on it 24hr to capture it’s light curve as it goes off. Doesn’t have to be expensive.

Nereid2
Member
Nereid2
November 17, 2009 3:11 PM

@Anaconda: it’s not exploding (as a supernova) yet … and may not do so, ever.

An ‘hourglass’ shape is a very common one, and can be produced by several different mechanisms (remember that the ‘shape’ in an astronomical image is merely a 2D distribution of the intensity of electromagnetic radiation detected).

Gomez’s Hamburger is one example (similar mechanism to V445 Puppis); M82 is another (rather different mechanism); and 3C272.1 a third (very different mechanism, although one may not consider to have a classic hourglass shape!)

Anaconda
Member
Anaconda
November 17, 2009 4:15 PM

DrFlimmer, I appreciate the explanation, but isn’t convincing, gravity would act in a spherical fashion and Nereid2’s attempt at explaining why a star close to exploding from old age and a star just forming would look alike.

Trippy
Member
Trippy
November 17, 2009 4:49 PM

I imagine that the similarity has to do with the objects being similar – as has already been pointed out, both types of objects are surrounded by thick disks, and have material flowing out rapidly…

The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
November 17, 2009 4:50 PM
V445 Puppis are among th so-called pre-Asymptotic Giant Branch (pre-AGB) stars, approximately between 5M? and 11M?s. These kind of objects are generally describe as the the Bipolar Planetary Nebulae. It is presumed that the gaseous shells surrounds will only feature prominently in particular areas, which in turn, become formed shapes of unusual structures of the nebula shell. They sometimes either asymmetric, symmetric or mirrored. Uncertain mechanisms exist for these strange structures, but many theorists now suspect these phenomena are strongly influenced by either fast stellar rotation, and display other secondary effects such as magnetic fields, or being associated as close binary systems. In evolutionary terms, these observed structures are related to the initial conditions of envelope ejection by… Read more »
The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
November 17, 2009 4:57 PM
In a verbal paper I’ve presented on these objects, the best quote I’ve found supporting the theory on these objects was written by the specialistt in the field, Bruce Bruce Balick best explains this shell thinning phenomena, in detail; “…Before the shell is punctured… the symmetry of the hot bubble begins to react to the axisymmetric distribution of the pressure ahead of it. For shells whose temperatures are constant (10^4K), the ram pressure follows the initial density distribution. Hence the bubble expands fastest along the symmetry axis where the densities are lowest. Eventually the hot bubble works its way to the polar edge of the shell where the pressure rapidly drops. Without the shell constraining it, the bubble… Read more »
The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
November 17, 2009 5:09 PM

To clarify one point.

When I wrote; “V445 Puppis are among the so-called pre-Asymptotic Giant Branch (pre-AGB) stars, approximately between 5M? and 11M?s.”

This is related to the progenitor, was mass was between 5 and 11 solar masses. These form heavy white dwarfs (WD), similar to the WD-oxygen story in Universe Today a few days back.

Sorry for the confusion.

Lawrence B. Crowell
Member
Lawrence B. Crowell
November 17, 2009 6:04 PM

Hon SB Crumb,

What you write is in line with how a lot of physics is done. You might have a dominant spherical process, but therre are perturbations or complicating processes. So the spherical term is perturbed by Bessel functions and so there are dipole terms and higher. These processes indicate how there are substantial dipolar processes at work, which likely in this case are due to MHD physics.

LC

Nereid2
Member
Nereid2
November 17, 2009 6:05 PM
@Anaconda: First, let’s address the “a star close to exploding from old age”. DrFlimmer, I appreciate the explanation, but isn’t convincing, gravity would act in a spherical fashion and Nereid2’s attempt at explaining why a star close to exploding from old age and a star just forming would look alike. Recall that Type Ia SNe are (as far as we can tell) the nuclear detonation of a white dwarf (WD) star … and that the trigger for the detonation involves the acquisition of mass (hydrogen, helium, in some mixture) by transfer from a close binary companion. The progenitor (of the Ia SNe – the almost-but-not-quite-at-the-limit white dwarf – would slowly dim, grow cold, and fade away … if… Read more »
Astrofiend
Member
Astrofiend
November 17, 2009 6:19 PM
The Wikipedia page on Planetary Nebula has a brief discussion of how the complex and often bipolar structures of planetary nebula may come about via the interplay of various processes. The cause of the interesting morphologies can be to do with asymmetries in the progenitor star or system, the interaction of out-flowing material moving at different speeds, the presence of magnetic fields, the presence of planets etc. The page has an interesting computer simulation showing the effect of a small stellar asymmetry leading to bipolar outflows. There are studies supporting variously all of these claims – some are more favored than others, but nobody would dispute that a lot more work is going to be needed to nail… Read more »
The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
November 17, 2009 6:47 PM
Lawrence B. Crowell Says: “What you write is in line with how a lot of physics is done. You might have a dominant spherical process, but there are perturbations or complicating processes. So the spherical term is perturbed by Bessel functions and so there are dipole terms and higher. These processes indicate how there are substantial dipolar processes at work, which likely in this case are due to MHD physics.” Magnohydrodynamics is certainly at play in the scenarios seen. The problem of course is the hugh diversity in forms amount bipolar outflows. The spherical model seems most important when the star throws it atmosphere away from the star. The whole visible shell we see is a consequence of… Read more »
Trippy
Member
Trippy
November 17, 2009 6:57 PM
AFAIK, no white dwarfs have been resolved, let alone imaged (i.e. every WD is indistinguishable from a point source. Similarly, no T Tauri star, or other pre-main sequence star, has been resolved (I am less sure of this though). A 1 solar mass white dwarf would have a radius of about 5,000 km (earth has a mean radius of 6,370 km). According to C. Pinte et al 2008 ApJ 673 L63-L66, the inner radius of a T-Tauri disk is about 0.42 AU, and according to M. Küker, Th. Henning and G. Rüdiger in Astrophysics and Space Science Volume 287, Numbers 1-4, who’s models, incidentally, accounted for magnetic influences on the proto-star and accretion disk, a 1 solar mass… Read more »
Nereid2
Member
Nereid2
November 17, 2009 7:47 PM

It’s actually an interesting exercise to try to think of all the ways a star (other than the Sun) may be imaged (at least in the UV/visual/NIR wavebands), other than as a point source.

There are several which will yield basic info such as radius, some measure of limb darkening, and some measure of gross shape – speckle interferometry, intensity interferometry, deconvolution of eclipse light curves (in eclipsing binaries), stellar occultations (by the lunar limb), more?

The light version of radio LBI (long-baseline interferometry) is just starting, and may produce reconstructed images of stellar discs (albeit with rather low S/N), and then there’s the technique for reconstructing starspots …

DrFlimmer
Member
DrFlimmer
November 18, 2009 4:59 AM

Great posts HSBC and LBC (and others). Complicated stuff, indeed, I will have to read it once or twice, again wink .

Does anyone know if there is a spectrum available of the outflow? If it is not exactly perpendicular to the line-of-sight, one should be able to detect Doppler shifts. This would clearly prove beyond any doubt that we have an outflow.

Lawrence B. Crowell
Member
Lawrence B. Crowell
November 18, 2009 6:17 AM
@Hon. Salacious B. Crumb, Of course the physics is seriously complicated. The dipolar structure here might be a precursor for a dipole supernova. I can’t comment on the structure of SN1s in detail, but some supernova events have dipole physics as well. So when the star explodes some instability, such as a dipolar MHD prescuror, might induce Rayleigh-Taylor instabilities or some other physics. These dipole terms might amplify in the shock wave physics of a supernova. So the whole thing might explode in a dipolar configuration. I am not theorizing, but making a plausible conjecture. To be honest I hope that does not happen. That would probably throw a huge monkey wrench on our standard candle calibration of… Read more »
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