The Sun as a White Dwarf Star

by Ian O'Neill on March 19, 2009

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Dusty debris around an old white dwarf star (NASA)

Dusty debris around an old white dwarf star (NASA)

What will happen to all the inner planets, dwarf planets, gas giants and asteroids in the Solar System when the Sun turns into a white dwarf? This question is currently being pondered by a NASA researcher who is building a model of how our Solar System might evolve as our Sun loses mass, violently turning into an electron-degenerate star. It turns out that Dr. John Debes work has some very interesting implications. As we use more precise techniques to observe existing white dwarf stars with the dusty remains of the rocky bodies that used to orbit them, the results of Debes’ model could be used as a comparison to see if any existing white dwarf stars resemble how our Sun might look in 4-5 billion years time…

A comparison of the Sun in its yellow dwarf phase and red giant phase

A comparison of the Sun in its yellow dwarf phase and red giant phase

Today, our Sun is a healthy yellow dwarf star. If you want to be precise, it is a “G V star”. This yellow dwarf will happily burn 600 million tonnes of hydrogen per second in its core for 10 billion years, generating the light that is required to make our planet habitable. The Sun is approximately half-way through this hydrogen burning phase, so it’s OK, things aren’t going to change (for the Sun at least) for a long time yet.

But what happens then? What happens in 4-5 billion years when the supply of hydrogen runs out in the core? Although our Sun isn’t massive enough to entertain the thought of going out in a blaze of supernova glory, it will still go through an exciting, yet terrifying death. After evolving through the hydrogen-burning phase, the Sun will puff up into a huge red giant star as the hydrogen fuel becomes scarce, expanding 200 times the size it is now, probably swallowing the Earth. Helium, and then progressively heavier elements will be fused in and around the core. The Sun will never fuse carbon however, instead it will shed its outer layers forming a planetary nebula.

Once things calm down, a small sparkling jewel of a white dwarf star will remain. This tiny remnant will have a mass of around half that of our present Sun, but will be the size of the Earth. Needless to say, white dwarfs are very dense, intense gravitational pull countered not by fusion in the core (like all Main Sequence stars), but by electron degeneracy pressure.

Relative sizes of IK Pegasi A (left), IK Pegasi B (lower center; a white dwarf) and the Sun (NASA)

Relative sizes of IK Pegasi A (left), IK Pegasi B (lower center; a white dwarf) and the Sun (NASA)

When the Solar System reaches this phase in its evolution, what will it look like? What will become of the asteroids, gas giants, moons and rocky planets? I was very fortunate to chat with astrophysicist Dr John Debes, from NASA’s Goddard Space Flight Center, at January’s American Astronomical Society (AAS) conference in Long Beach (California) who is developing an n-body code simulating an evolving Solar System.

After the Sun has stopped hydrogen fusion in its core, it loses mass as it sheds its outer layers after the red giant phase and subsequent planetary nebula formation. It is estimated that the Sun will lose about 50% of its mass during this time, naturally affecting the Solar System as a whole. As the Sun loses mass, the outer planets (such as Jupiter) will drift outwards, increasing their orbital radii. In the simulation, Debes is very careful to ensure there is a gradual reduction in solar mass to ensure stability in the simulation.

What we are left with is an old Solar System, where little is left of the inner planets (it is likely that anything within the orbit of the Earth will have been swallowed by the Sun as it expanded through the red giant phase). Although the future white dwarf Solar System will seem very alien to present day, some things won’t change. Jupiter’s orbit might have receded with the drop in solar mass, it will remain a planetary heavyweight, causing disruption in asteroid orbits. Using known asteroid data, the motion of these chunks of rocks are allowed to evolve, and over millions of years, they may get thrown out of the Solar System, or more interestingly, pushed closer to the white dwarf. Once the whole system has settled down, resonances in the asteroid belt will become amplified; Kirkwood Gaps (caused by gravitational resonance with Jupiter) will widen, and according to Debes’ simulations, the edges of these gaps will become perturbed even more, making more asteroids available to be tidally disrupted and shredded to dust.

Artists concept of shredded asteroid around white dwarf (NASA/JPL-Caltech)

Artists concept of shredded asteroid around white dwarf (NASA/JPL-Caltech)

The AAS conference was full of amazing research into white dwarf observations. The reason for this is that there are many white dwarf candidates out there with dusty metallic absorption lines. This means that there used to be rocky bodies orbiting these stars, but became pulverised (by tidal shear) for astronomers to analyse. These white dwarf systems can give us a clue as to what mechanisms could be supplying the white dwarfs with dusty material, even giving us a glimpse into the future of our Solar System.

We have a physical picture for the link between planetary systems and dusty white dwarfs,” Debes said when describing his model in relation to the mysterious dusty white dwarf observations. “Dusty white dwarfs are truly a mystery! We think we know what might be going on, but we don’t have a smoking gun yet.”

However, Debes is getting close to finding a possible smoking gun, he’s basing his model on some of the key characteristics of these ancient dusty remnants to see what the Solar System could look like in billions of years time.

So, where does this dust come from? As the asteroid orbits are perturbed by Jupiter, they may get close enough to be tidally disrupted. Get too close and they will get shredded by the gravitational shear created by the steep tidal radius of the compact white dwarf. The asteroid dust then settles into the white dwarf. The presence of this dust has a very obvious signature in the absorption lines of spectroscopic data, allowing researchers to infer an accretion rate for metal-rich white dwarfs. In Debes’ model, he has set the upper limit to 1016 g/year and a lower limit to 1013 g/year, consistent with observed estimates.

Spectra of G29-38. Could this resemble the spectra of the Sun after turning into a white dwarf? (NASA/Spitzer)

Spectra of G29-38. Could this resemble the spectra of the Sun after turning into a white dwarf? (NASA/Spitzer)

In his evolved Solar System model, Jupiter’s gravity controls this accretion rate, pushing asteroids toward the white dwarf and, by using a powerful supercomputer to track the perturbations and eventual shredding of known asteroids, there may be an opportunity to arrive at a profound conclusion. Debes is able to use his model to compare observations of known dusty white dwarfs with the simulated outcome of the Solar System. With reference to previous studies (in particularly Koester & Wilken, 2006 in the journal Astronomy & Astrophysics), Debes has found some similar white dwarf “Suns”.

For G29-38, the canonical dusty white dwarf, they [Koester & Wilken] estimate a total mass of 0.55 solar masses–about what people believe the mass that our own sun will have remaining when it becomes a white dwarf,” Debes added. “But mass estimates are a bit uncertain–I’ve seen estimates ranging from 0.55-0.7 solar masses for this particular white dwarf.”

The Su<span>n's future? The whit</span>e dwarf G29-38 (NASA)

The Sun's future? The white dwarf G29-38 (NASA)

Another good candidate is a DAZ [a metal-rich white dwarf] called WD 1257+278, which does not show dust but is spot on with the mass expected for the Sun–0.54 MSun,” said Debes. “Its accretion rate is also consistent with my model predictions so far assuming an asteroid belt mass and characteristic perturbation timescale that I found in my simulations.”

Debes is continuing to make his model more and more sophisticated, but already the results are promising. Most exciting is that we may already be observing white dwarfs, like G29-38 or WD 1257+278, giving us a tantalizing glimpse of what our Solar System will look like when the Sun becomes a white dwarf star, ripping apart any remaining asteroids and planets as they stray too close to the Sun’s tidal shear. However, it also raises the question: if white dwarfs like G29-38 are being fed by the remains of tidally-blended asteroids, are there massive planets shepherding asteroids in these white dwarf systems too?

About 

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Hello! My name is Ian O'Neill and I've been writing for the Universe Today since December 2007. I am a solar physics doctor, but my space interests are wide-ranging. Since becoming a science writer I have been drawn to the more extreme astrophysics concepts (like black hole dynamics), high energy physics (getting excited about the LHC!) and general space colonization efforts. I am also heavily involved with the Mars Homestead project (run by the Mars Foundation), an international organization to advance our settlement concepts on Mars. I also run my own space physics blog: Astroengine.com, be sure to check it out!

Olaf March 19, 2009 at 4:44 PM

Salaciousn can you explain it is simple lifeform terms. ;-)

A bit too abstract your explanation of Oils for me.

Do you mean he is religious and wants to get rid of all heritics?

OilIsMastery March 19, 2009 at 5:44 PM

Layman,

“If you do not believe in the Big Bang- what do you believe?”

See here: http://www.bigbangneverhappened.org/

“…their theory is incorrect but they don’t have an accepted theory to replace it and that I think is very psychologically bothersome to particularly scientists who have gone into science in order to be certain about the world, to be sure that they’re right and so forth, and it’s a very insecure position. Some scientists have joked that well a scientist would rather be wrong than uncertain. We sort of have to live with uncertainty which is, well, it’s an interesting and challenging situation.” — Halton C. Arp, astronomer, 1998

“And do you have proof of your beliefs?”

Yes. Electrons and electricity have been observed and tested. They are not just a little trick that you can repeat in the lab. All matter is coposed of electricity and all inertia of electromagnetic origin.

“Also how old do you believe that the Universe is- 14 billion years? 6000?
Just curious”

I have never observed the entire universe so I can’t comment on it’s age. Time is a priori so I’m not sure the universe even has an age.

Layman March 19, 2009 at 6:26 PM

Oillsmastery- Thank you for setting us straight on your beliefs.
I read your recommend sight-bigbangneverhappenen.org
I am not a scientist and to be perfectly honest this is my first view of Plasma theory- Most of it is way over my head.
It does go against popular thoughts of currently accepted conventional scientific wisdom.
I have always had a problem with Inflation theory just to make the Big Bang math work- It may well be correct, but how can we ever prove it? In my mind this becomes more like religion- I want more than a faith based science.
What I do know is that it appears that we live in a very large Universe and that we may never know what happened before there was nothing. Black holes seem to exist whether you like it or not. Gravity seems to hold things together or push them apart. Dark matter/dark energy- time will tell…..
We will talk about this again in 5 or 10 thousand years and see what has been learned.

pantzov March 19, 2009 at 6:42 PM

keep givin’ them hell oills!

i’m not all that into your plasma theory, but i do like how you are never afraid to question the limits of what we know.

OilIsMastery March 19, 2009 at 7:04 PM

Layman,

“Black holes seem to exist whether you like it or not.”

Where? In Meinong’s Jungle?

“…the ‘Schwarzschild singularities’ do not exist in physical reality.” — Albert Einstein, mathematician, 1939

“Even mainstream scientists admit that at singularities the ‘laws of physics’ break down. It would be more accurate to say that their own theories break down.” — David Pratt, natural philosopher, 2005

popisfizzy March 19, 2009 at 9:43 PM

I can’t find anything verifying the existence of the David Pratt fellow you speak of, except for quotes which seem to indicate he’s strangely inline with fringe physics. I can see that your quote there is properly attributed to Marcus Chown of New Scientist though. Of course, he’s talking about how our current theories are incomplete and need more refining, i.e. a quantum theory of gravity. Chown (and not this likely non-existance Pratt fellow) isn’t saying that black holes don’t exist.

OilIsMastery March 19, 2009 at 11:28 PM

Popisfizzy,

“I can’t find anything verifying the existence of the David Pratt fellow you speak of, except for quotes which seem to indicate he’s strangely inline with fringe physics.”

I agree with you characterization of Albertin Einstein and General Relativity as “fringe physics.” However, Einstein happened to be correct about black holes.

“I am inclined to think that physicists will not be satisfied in the long run with this kind of indirect description of reality, even if an adaptation of the theory to the demand of general relativity can be achieved in a satisfactory way. Then they must surely be brought back to the attempt to realise the programme which may suitably be designated as Maxwellian: a description of physical reality in terms of fields which satisfy partial differential equations in a way that is free from singularities.” — Albert Einstein, mathematician, 1931

popisfizzy March 20, 2009 at 1:06 AM

Oooh, and twisting words now, eh? You’re rather good at being a crank. Of course, I was talking about quotes from “him” (as attributed by a person with your mannerisms, meaning it was likely you) believing in the expanding Earth theory, which is fringe because there is no viable method for expansion.

And Einstein dislike black holes because of singularities, which is considered a problem in modern physics, likely remedied by a quantum theory of gravity. Of course, he didn’t believe quantum mechanics either. Einstein, and all physicists, are hardly infallible. But they’re certainly less fallible than you, with your quoting and rambling and ignorance and lack of evidence. Silly little man. :P

Sir Arthur Wellesley March 20, 2009 at 1:37 AM

I hope this doesn’t sound stupid but if the orbits of the outter planets change wouldn’t the inner planets orbit change?? Perhaps pushing earth into a deeper orbit so it wouldn’t be consumed?

Excalibur March 20, 2009 at 2:03 AM

Sir Arthur Wellesley:

Correct, as the Sun is expelling mass, all orbiting planets will slowly migrate outwards.

However, as the sun is also expanding, some of the inner planets might get atmospheric ‘drag’ that makes them loose orbital momentum aswell. Inside some limit they would therefor migrate inwards and end up being swallowed.

Feenixx March 20, 2009 at 4:22 AM

Olaf Says (about OilIsMastery):
“On a holistic site he would have some credibility,”

I don’t believe he would. His views often come across to me as reductionist, insular and and protectionist.
I very strongly believe in holism – a belief which provides the basis for my fascination with science, my fascination with observing how the “Big Picture” never quite allows itself to be drawn by “joining the dots”, no matter how precisely those dots are positioned, and how many of them can be defined.
OIM, on the other hand, in a manner of speaking, seems to consider a picture he likes and search for dots, which he then claims can be joined to produce the chosen picture.

I can see some mainstream scientists driven by reductionist thinking – others driven by holism… and I continue to be fascinated while looking in awe at the Universe around me….
… and I continue to drift off-topic. My apologies, but at least I’ve got this niggle off my chest now.

AJames March 20, 2009 at 8:38 AM

Feenix
I do agree with everything you said in the above post except that you did not go far enough. I.e.

I can see some mainstream scientists driven by reductionist thinking – others driven by holism…

In truth, the most successful among scientists and engineers, and indeed partly in the practical sciences, are the ones who can easily switch between holism and reductionism in their thinking – then apply it to the situation requires. Being involved in investigation often need formal and apt application of the scientific method, but every now and then you must look at where it fits into the big picture. Here lies the spark of inspiration, whose insight leads to different ways of thinking or new avenues to explore. For example, Einstein and others seem adept to the switching between these two scientific philosophies. (I.e. The applications passing of trains relative to one another in the experienced part of the world and the when travelling at light speed. Found later in say the increased mass of a proton as it is accelerated to near light speeds.) Also, such ways are often seen with scientists or engineers who are also brilliant in formal education.
I am more amazed at some of the scientists, and many cosmologists who are just fanatical purists of just reductionism. General characteristics are ones who are diligent in the data produced and the painstaking analysis to draw the correct logical conclusions. However, most fail dismally in how their work fits into others or the branch of science they specialise.
Holism is also useful in examining various cracks in theory, and then assessing which one is the best option to discover new concepts or avenues to deeper understanding.
Oils is vulnerable because he absolutely fails to see the true meaning of the scientific method and the reasoning behind it. Instead, he rejects it outright and relies on crazy faith-based philosophies as the means of defining truth. Those who do not follow the path based on doctrine must be wrong (heretical thinking), so the purpose is to expose the weaknesses of accepted Theory – and finding one fault then completely rejects the whole notion of that theorem. I.e. Gravity waves have not been found, therefore gravity doesn’t exist at all. Hence for him it is all or nothing, when the reality is we understand what we perceive as the consequences of mass and the force it exerts very well, but we have yet to absolutely determine the manner of transmission that gives mass its characteristic signature.
The classic example of holism, which exposed Anaconda’s weakness in understanding, was Noether’s Theorem – in which Emily Noether importantly joins the physical systems of symmetry to their corresponding conservation laws. She, for example, is a prime candidate for the profound insight of things through holism. This was help no doubt to the sexist world of science 100 years ago, who applied an missed insight into nature on behaviours of most physical systems.

Feenixx March 21, 2009 at 4:26 AM

AJames says:

[quote]In truth, the most successful among scientists and engineers, and indeed partly in the practical sciences, are the ones who can easily switch between holism and reductionism in their thinking – then apply it to the situation requires.[/quote]

Bang on, enough said!
Thanks for filling in the “missing bit” in my post. :)

Sir Arthur Wellesley March 21, 2009 at 6:18 AM

Excalibur

Thanks for the reply, interesting stuff indeed!

Salacious B. Crumb March 21, 2009 at 7:48 AM

Feenix.

Here is a definitive quote by Einstein towards holism that might help you;

“…in truth the relationship between fundamental laws and facts from experience is not that simple. Indeed, there is no scientific method to deduce inductively these fundamental laws from experimental data. The formulation of a fundamental law is, rather, an act of intuition which can be achieved only by one who watches empirically with the necessary attention and has sufficient empirical understanding of the field in question. The sole criteria for the truth of a fundamental law is only that we can be sure that the relations between observable events can be logically deduced from it. It follows then that a fundamental law can be refuted in a definite manner, but can never be definitely shown to be correct, as one must always bear in mind the possibility of discovering a new phenomenon that contradicts the logical conclusions arising from a fundamental law.” — Albert Einstein 1925

(Just don’t tell Oils…)

Cheers

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