We've spotted a planet surviving its dying star | Hacker News Reader

We've spotted a planet surviving its dying star

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182 pointsgmays69 comments

Perhaps I missed it, but I'm curious to how they know this is a planet which survived the red giant phase vs. a planet which was captured afterwards (or formed from the debris caused from the star -> red giant -> white dwarf transition). Maybe it's covered more in actual paper.

They mention in the article that a handful of previously discovered planets orbiting white dwarfs are believed to have arrived after transition due to their orbits.

Published at https://www.nature.com/articles/s41586-021-03869-6 . "Dying" refers to "survive the volatile evolution of their host stars into white dwarfs."

Out of curiosity, the video part way down ("White Drwarf System Animation Text") showing the dying star... how are these videos created? Is it done in something like Blender? The video credits Keck Observatory, do they have 3d artists on staff for this kind of thing? Do Astronomy grad students just learn how to create visualizations? What's the turnaround for getting something like this made because I'm assuming it was made for the press release.

I work for the Keck Observatory (engineer). Far as I know we do not have any 3D animators on staff. We produce images from our science instruments for the astronomers to download and they all eventually end up here: https://www2.keck.hawaii.edu/koa/public/koa.php

The first extrasolar planets discovered had survived a supernova explosion: https://en.wikipedia.org/wiki/PSR_B1257%2B12

"Dying" is a bit of an under-statement. A white dwarf is to all intents and purposes dead. It has no source of energy, and radiates only because of stored heat.

That heat dissipates so slowly that (AIUI) no white dwarf in the universe has yet had time to cool down enough to stop radiating (i.e. the universe does not yet contain any black dwarves).

So a star that is in the process of collapsing into a white dwarf could reasonably be said to be "dying". Once it's collapsed, it's dead.

How would we see black dwarves?

If there were bright things behind them

The universe is young, a lot of stuff hasn't happened yet. It wouldn't be surprising if we are about the earliest life of this sort that could exist.

I thought the cosmological expansion theory of the standard model was falling apart calling into question the Big Bang theory. If that’s the case, then are we sure we have a good handle on the age of the universe?

Do you have any links where I can read more about that? That's fascinating and I wasn't aware, and I evidently am not using the right search terms to find out more

Maybe unrelated but YouTube has been throwing a lot of faux science and astronomy at me lately. Youtubers reading controversial papers presented as indisputable even when there's no scientific consensus at all on the results.

It's depressing to think about, but for many intents and purposes fake space facts are just as good as true space facts.

Especially for purposes of monetizing YouTube videos.

I believe they’re referring to the “crisis in cosmology”. I’m purely a layman, but I found some videos useful. I believe at least PBS Space-Time [1] is well regarded in physics circles (for laymen explanations.). I found the other one [2] to be more digestible though.

[1] https://youtu.be/72cM_E6bsOs

[2] https://youtu.be/0sfvQ_fsil4

Depends on your perspective I suppose. Most of the stars have already formed and star formation will slowly grind to a halt in a few billion years.

old and young universe then :)

At least, I can understand visualize the time scale of the universe a lot better than I can visual the length scale. Speed of light doesn't feel like 1/1 to humans!

A BD is still hotter than background temp, so you could maybe see faint IR, and you could initially find it as a result of its mass if there are nearby objects orbiting (although now less illuminated), or simply transitioning in front of other stars (I guess that's how they find wandering planets?).

Alternatively, map all the white dwarves, then wait long enough, then look again..

You'd probably also be able to see white dwarves that were on their way to being black (whatever the threshold is).

There's no hard threshold, the star just fades gradually from #FFF to #000.

A fully black dwarf would be so cold it would be indistinguishable from cosmic background radiation, but that's going to take at least a trillion times longer than the current age of the universe. Not just slightly longer.

Right. I'm just saying that if the are any black dwarfs (which there should not be), we should be able to find ~arbitrarily dim ones as well, down to our ability to see.

Given there are no BDs (so they are theoretical) maybe there isn't a threshold defined?

A WD will slowly cool to a BD over Trillions of years, so it's all linear. Funnily enough, they are probably every shade of red/brown in-between - but "brown dwarves" are usually reserved for objects that never where "proper" hydrogen-fusing stars, but are large enough to fuse deuterium.

Gravitational lensing, most likely.

Possibly through gravitational interactions with non-dwarf stars in the same system.

There not being any yet makes either method somewhat more challenging.

https://www.scientificamerican.com/article/living-near-a-whi...

I’ve always found this idea neat.

> By damping trash onto the surface of the white dwarf, one could harvest its gravitational binding energy from the emitted electromagnetic radiation at nearly the yield of nuclear fuel.

This sounds interesting, how would such a method of power generation work?

Well, that very nearly is the method of power generation. It would presumably be paired with some sort of Dyson sphere around the white dwarf. (Remember that a "Dyson sphere" isn't necessarily a solid shell, but just some configuration of matter where no matter which direction the energy goes it is intercepted by something.)

You may also enjoy: https://www.youtube.com/watch?v=t-O-Qdh7VvQ which is a minutephysics on black hole power using much the same principles but attaining yet higher efficiencies.

So we would decelerate the trash, it hits the white dwarf, gets crushed, and then undergoes various nuclear transformations resulting in energy output we would then capture with our Dyson swarm?

Sorry, but it has to be rigid to be a sphere. Angular momentum is a bitch!

PS: Dyson Spheres is misnomer, Olaf Stapledon should be credited for this idea (Star Maker 1937)

I've read somewhere that we now have a ton of junk satellites orbiting earth, and if they happen to crash into each other it could set off a chain reaction that creates a satellite-debris shell around the entire earth, roughly resembling a non-rigid sphere. Is that true?

That's roughly the story in the movie Gravity.

Collisions between orbital junk are most likely to happen between objects in the same orbit. And most junk is in some roughly equatorial orbit. So I'd expect the resulting debris to end up in roughly the same orbit, so that the debris would form a sort of fuzzy disk - not a sphere. I wouldn't expect to observe much debris over the North Pole.

That's more about why "sphere" is a misnomer that leads people to think the idea requires a large rigid shell than a problem with the idea. You can create configurations of matter that continuously and completely englobe a star without it being a rigid sphere. What you can't do is make it so that any other configuration is always receiving sunlight at all times because no part of it ever in shadow, but that is not a requirement to capture all energy from a star, that's merely an engineering question around efficiency.

The result may not be literally a rigid sphere as people think of it, but if the orbits are packed tightly together enough it'll look plenty "sphere-like" from the next star system over.

A rigid Dyson sphere is probably impossible, and its utility is not entirely clear. Making a Dyson swarm around a star is merely a lot of work, and also has the advantage of immediately paying benefits as soon as the very first satellite is launched.

Is "damping" a technical term, distinct from "dumping"? The article uses it more than once so it seems deliberate...

Damping is a physics or maths term. To damp means to (steadily?) decrease the amplitude of a wave or oscillation.

Damping is generally a technique which reduces, slows, or restricts a system. It is not a synonym for dumping. We have old, related terms like the "damper" on a fireplace, which I suspect may invoke a more basic analogy of putting water on wood fuel, i.e. making it damp and slower to burn.

In modern usage, "damping" usually refers to a drag or parasitic affect in some oscillatory system, but it does not have to be oscillatory. It can be other drag effects that convert energy, with a usual assumption that it will bring the system to a new equilibrium. An object falling through the atmosphere can be considered to have its fall dampened by the air drag, converging towards its terminal velocity.

I am not familiar with all the physics involved in falling towards/into such a star, so I do not know if there are field effects which would cause damping of the fall prior to impact of the trash with an actual surface, similar to the atmospheric descent towards earth. I also wonder if they imagine the orbital system is being damped to allow the trash to impact the star, by bleeding off tangential velocity to decay the orbit.

An informative piece, thanks for sharing. (Being tidally locked complicates the situation, I think.)

"Dying" is not referring to the state of the star today, but to the process of death: the planet survived while it's star was dying, which is the interesting bit of the story.

Agreed.

To survive in orbit around a WD is not a remarkable achievement - you just carry on orbiting forever (roughly). Orbiting a red giant would be pretty interesting, though - the RG has an indistinct surface, its diameter and luminosity varies, and it emits a lot of material as wind.

To survive in orbit around a neutron star would be another thing again. Neutron stars have intense magnetic fields, and spin rather quickly, resulting in a rotating field that is wrapped around on itself. That in effect creates a particle accelerator, driving electron flows (the electrons were all expelled when the NS collapsed) with extreme energies.

Short of hanging around near an exploding supernova, I can't imagine a more hostile environment.

Would the magnetic fields of a neutron star create a tidal locking effect through eddy currents in the planet’s core, boosting it into a larger orbit and slowing the spin of the star? Seems like a giant inside out induction motor.

I wonder what the band of survival is, where the planet doesn’t get turned to Swiss cheese first.

I have no idea what the neighbourhood of a neutron star is like, nor what the effects of such intense fields might be. This is theoretical physics and cosmology. I'm not competent even to speculate.

Yes, I get the "induction motor" idea. With fields and voltages that intense, I guess just about anything becomes conductive.

[Edit] I don't know whether those field strengths are consistent with atoms continuing to be atoms - I guess there must be some range beyond which a thing like a planet could maintain its integrity. But (guessing wildly) I would expect there to be a region around a neutron star within which it is impossible for atoms to exist.

Newly discovered Click-Bayitt type stars

Next you are going to say that a phone is dead unless it's being charged.

Please explain how a "charger" for a white dwarf might work! I mean, you could just chuck a huge ball of hydrogen at it; that might work, but it'd be easier to just bundle together two balls of hydrogen and make a new star.

I think I'd expect a charger to restore a phone to something like its as-new functionality. I've never heard of any mechanism that could change a white dwarf into not a white dwarf, other than extreme age, or being merged with another object.

The star gets charged up then gets to live a much longer life as a white dwarf.

You haven't been as-new since the day you were born and we both agree you are still in your life.

The classic short story "A Pail of Air" (1951; <https://en.wikipedia.org/wiki/A_Pail_of_Air>) depicts human survivors of a frozen Earth without the Sun.

Why would the planet be destroyed or have it's course altered ? The Star's mass remains the same and so does the gravity. Wouldn't the planet's own gravity hold it up when it's engulfed, and retrain shape when the star becomes a white dwarf ?

Well, there would be some extra drag, for one.

Not an astrophysicist, but it might get torched, blown away by the initial shockwave, or maybe drag between the planet and the solar atmosphere will slow its orbit into a collision course.

> The Star's mass remains the same

What makes you think so? I'm no expert, but matter is definitely expelled in the process of forming a white dwarf. The stuff scouring the inner planets doesn't appear out of thin air...

This random paper also appears to say that the mass lost is on the order of half the initial mass:

https://iopscience.iop.org/article/10.3847/1538-4357/aadfd6/...

> total stellar mass loss ranges from 33% of M_initial at 0.83 M_sun to 83% of M_initial at 7.5 M_sun.

I assume this would accelerate global warming.

Sol is gas, right?

Gasses cool when they expand, right?

What’s the expected surface temperature of Sol after it has expanded past Earth’s orbit?

Looks like it will drop to about half the current surface temperature as it expands (although this seems to be talking about it at around 0.5 AU) http://www.astronomy.ohio-state.edu/~ryden/ast162_4/notes15....

Thanks for the link. I wonder what temperature prevails at 1.0 AU.

On the one hand, artists’ conceptions of boiled oceans and cities in cinders that saddened and discouraged me in my childhood. On the other hand, the heat energy density of Sol today is comparable to a compost heap. When the radius of a sphere doubles, it’s volume increase eight times.

If Sol is too itsy to start helium fusion, maybe orbiting within the post-expansion photosphere - the hydrogen envelope - is chill, damp, and sparky?

The sun won't (potentially) swallow up the Earth for about 8 billion more years. The carbon cycle on this planet will have ended about 7 billion years before then; the increased output of the sun will have boiled away the oceans; plate tectonics will stop, etc. There won't be anything alive on this planet left to see the sun burn out.

Sounds bad for surface life. Morlocks live underground.

> How will the Solar System die? It’s a hugely important question

Why?

Because it's where we live?

It's not. At least not right now. But probably something we should revisit in around 2 billion years. (using we loosely to mean whatever entities humans have become by then). Although it might be cool to get a shout-out from the apex species of 2,000,002,021... we'd like to thank Homo Sapien sapien for first bringing this to the attention of sentient life in this solar system

If you write an article with "we spotted", then please provide some image material, even if only a graph.

While I'm no astrophysiyst I don't think it's a matter of 'their sun was there last week, look, this week it's not' and nor do I think an artist's impression of something orbiting nothing adds any more, nay, indeed adds nothing, to the written description.

The paper contains figures like [1] or [2], which I think do add something to the written description (and obviously the paper authors thought so too, otherwise they wouldn't have included it in the paper). These visuals are quite useful when talking about what we mean by "spotted" (though the context is important and the article only spends maybe two paragraphs on the actual observation method, so there's some danger of misinterpretation)

1: https://www.nature.com/articles/s41586-021-03869-6/figures/1...

2: https://www.nature.com/articles/s41586-021-03869-6/figures/7

Those images would be copyrighted, so may not be available to the publisher of the article.

Where are all the graphical artists at?

We had an Ask HN here, like yesterday.

I'm sure the authors and their institutions would be happy to grant the right to use the images in an article about the paper if somebody asked them. Publicity for the finding is in their best interest. Unless their publishing agreement with Nature restricts this, not sure how strict exclusivity is in those cases

In some cases, for some papers it might be possible to eventually get rights to the charts that would satisfy your own publisher's legal department yes. They'd have to jump through those hoops every time though, and time is money.

It seems to be the cool thing to do lately. Especially if you have a visual web app, a tool that has a functional GUI component, or a breaking story about the planet or a new piece of hardware, you must make sure not to include the one thing that would make it most worthwhile -- a picture.

You'd probably be disappointed. The best you could hope for is a graph of luminous flux vs time, showing the slightest decrease as the planet transits some emission nebulae.

Astronomy "images" are computer generated anyway, often with artistic touches.

Isn't that just a simple formula? I even seen planet destroyed/remains on some of stellar evolution simulators.

It all depends on orbit radius and star mass at the end of Asymptotic Red Giant Branch.

Note that white dwarves aren't stars but rather stellar remnants without energy source.

But, who wants to live forever?

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