Boffins baffled by planet nugget whizzing round white dwarf that should have killed it Astronomers have discovered an object that orbits dangerously close to its parent white dwarf star. It should have been crushed to death by the dying star’s gravitational pull, but has miraculously stayed intact somehow. “The planetesimal we have discovered is deep into the gravitational well of the white dwarf, much closer to …
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I have heard about this, but I haven't seen the data yet. There are three plausible explanations for this:
1. It's an outer planet that migrated inward. When the star shed its outer layers to become a planetary nebula, an outer planet started plowing through the material and lost energy thereby spiraling in on the white dwarf. When the planet got closer, it disintegrated leaving just part of the core. A variation of this is that it is an iron (or metallic) asteroid that migrated inward.
2. The planet survived the death of the star, although this is highly unlikely. Mercury and Venus will be engulfed by the sun at the end of its life. As the planets plow through the solar material that the sun will puff off, the planets will lose energy and spiral inward. The high-energy plasma that makes up the star will evaporate the planets until there is nothing left. Even an iron core will not survive. Additionally, wildly shifting gravitational forces will cause uneven tidal pressures on the planets and they will be ripped apart. Earth may or may not be consumed in this way.
3. The planetoid formed (or reformed) after the star died and became a white dwarf. There is a fair amount of heavier elements such as silicon and oxygen (mostly hydrogen and helium though) which enabled a planetoid to form there.
Given these three possibilities, I think #1 is the most likely scenario. And yes, I am an astro-boffin.
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Thank you for explaining this. I am passionate about space, but I am no astronomer. I would like to know though : is there any chance that, while our Sun is puffing up and turning red, the Earth's orbit will slowly get larger as the Sun's density goes down ?
I have not found any actual answer on this yet, despite scouring excellent resources such as PBS Eons and SciShow Space on YouTube, not to mention numerous TED talks. Nobody has a definitive opinion on this, it would seem.
Would you have any information to share on that point ?
"It should have been crushed to death by the dying star’s gravitational pull...".
I thought the mechanism was pulling apart, rather than crushing (Roche limit).
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Their physical size is comparable to that of earth, so yes, they are small. According to the kepler's third law calculator I just used the orbit is around 500 000 km which is a little less than the radius of our own sun. The orbital velocity would be around 400 km/s.
The fact that they collapse to such a small volume allows you to fall pretty deep into the gravity well.
The 'year' is two hours long only because it's a few hundred thousand km from the white dwarf. Roughly speaking, a white dwarf packs the mass of the sun into a volume the size of the earth.
If the object is indeed slowly spiralling in as it plows through gas surrounding the white dwarf, it will eventually be orbiting at "treetop" level, whirling around about once every ten seconds at about 1% of the speed of light (again going with that one-solar-mass, one-earth-radius approximation). At its present distance, tidal forces on this rock are not all that significant (i.e., not much pulling it apart). Once you get closer in, it'll get pulled apart and it'll be bits of gravel that do the treetop orbiting. (Though I just did the math... if you were in a spaceship 200 meters/metres across in this "treetop" orbit, you'd feel no gravity at the center, about +1 gee toward the white dwarf if you were on the side toward it, and -1 gee if you were on the side away from it.) A spaceship would hold up under this; a rock would probably fall apart.
Those expecting you'd be ripped to shreds, a la Larry Niven's _Neutron Star_, are probably forgetting that a neutron star is about a hundred times smaller than a white dwarf. Tidal forces go as the _cube_ of distance; try a treetop orbit on a neutron star, and you _will_ be finely shredded.
"So how tall are the trees on a neutron star?"
Teentsy.
See "Dragon's Egg" by Robert Forward. I'd advise reading the Wiki page after the novel because the novel is sort of written like a detective story or a series of scientific discoveries. It's a good story, well-written.
. https://en.wikipedia.org/wiki/Dragon%27s_Egg
So far, our astroboffins have found TWO small but incredibly tough objects orbiting dying stars in the Virgo constellation. Objects that the boffins were not expecting and whose presence baffles said boffins.
I think we should avoid the Virgo constellation in our future space exploration, sounds like a bit of a rough and tumble neighborhood. Perhaps aim for somewhere soft and fluffy instead, or even one of those systems with the diamond-like star in the center. Let's leave the Virgo guys alone for a while longer until we can toughen up a bit. Maybe just observe from a distance of a few light years until then.
Those are already dead stars. This are the leftovers. Just wait 9 billion years and this is going to happen to our solar system. Earth has only 700 million to 2000 million years left and then everything is going to be burned off planet Earth.
Estimation of what is going to happen in the far future.
https://en.wikipedia.org/wiki/Timeline_of_the_far_future
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