General Astronomy Questions

[JMBuilder]

1. What does a completely dead white dwarf look like? Is it like a solid planet?

2. Are neutron star "fragments" a real thing? Can the "fragments" continue to sustain their reactions?

3. How big would a neutron star with the mass of an average-size planet be?

4. Do bigger stars have bigger habitable zones?

5. Say you had a binary-ish star system consisting of a massive star and a relatively low-mass star. Is it possible to have planets stably orbiting the massive star further out than the lower-mass star?

[Sirad]

1 hour ago, JMBuilder said:

4. Do bigger stars have bigger habitable zones?

As for this one i can answer:

The Bigger the Star (in Terms of Mass) the lesser the 'Habitable Zone'. Radiation emitted from 'Bigger' Stars tend to have much shorter Wavelengths so the Radiation has a much more Fatal impact upon us Carbon Based Lifeforms. Big Blue Monsters Radiate that much Energy and High energetic Particles, that even any Atmosphere or Magnetic Field any Planet can come up with, gives absolutely no protection. Given that, Bigger stars even have much shorter Lifespans (500M Years and even much less)

Think of a Solar Wind that high Particle momentum, equal out of CERN.

Any Atmosphere given in any potential Habitable Zone around a Big Blue One will be Eroded by sheer radiation Pressure from Solar Wind. So will any Liquids & Longer Molecules be Destroyed/Ionized by impact Momentum of Photons/Particles.

Bigger Star = shorter Lifespan = more Radiation = lesser habitable Zone

Smaller Star = longer Lifespan = less radiation = bigger habitable Zone

hope i could helped.

[UmbralRaptor]

1 hour ago, JMBuilder said:

1. What does a completely dead white dwarf look like? Is it like a solid planet?

2. Are neutron star "fragments" a real thing? Can the "fragments" continue to sustain their reactions?

3. How big would a neutron star with the mass of an average-size planet be?

4. Do bigger stars have bigger habitable zones?

5. Say you had a binary-ish star system consisting of a massive star and a relatively low-mass star. Is it possible to have planets stably orbiting the massive star further out than the lower-mass star?

1. Dead as in what? The white dwarf stars we can observe are, well, white-hot. If we assume cooling times far longer than the present age of the universe, then one could presumably get more planet-like conditions. Sort of.

2. "fragments" as in what, and what do you mean by reactions? The high densities/pressures necessary for the weirdness of neutron star interiors cannot exist without lots of mass if that's what you're getting at. The exact amount would require rather detailed calculations, though.

3. Planetary masses mean you have nowhere near enough to maintain neutron degeneracy, and even electron degeneracy only becomes a thing somewhere in the Jupiter to brown dwarf range. Again, "size" is not that well defined, and especially not average. Do you mean mass, diameter, or something else, and what kind of planet (earth-like, super-earth, ice giant, gas giant, something else)?

Ignoring the confinement problem, and assuming spheres with a density of 1e17 kg/m³, though:

Body	Mass (kg)	Neutronium radius (m)
Mercury	3.302e23	924
Earth	5.9736e24	2425
Neptune	1.0243e26	6290
Jupiter	1.8986e27	16549

So somewhere between <1 km to <17 km radius for most planet-like masses. But these numbers are only meaningful in a /r/theydidthemath/ sense.

4. I'm going to assume that "bigger" means higher mass main sequence star, in which case, yes. The greater luminosity means that the habitable zone is further out and due to the way the inverse square law works will have a greater volume.

5. If you organize things correctly, yes. Ish. Really the planets are orbiting the mutual center of mass of the two stars, and this works best if the stars are in a somewhat close orbit.

[kerbiloid]

If you tear a neutron star to pieces, those pieces keep so much energy, that once nothing presses them from around, they immediately will turn into an overheated gas with no chemical bounds of course 
So probably you would see just something like a supernova or so, with clouds of ionized gas getting cold.
Heavy particles contained inside are usually very short-living and should decay right during this burst.

Edited June 10, 2016 by kerbiloid

[JMBuilder]

By "dead white dwarf," I mean the remnant of a white dwarf after it has completely cooled down. Would it basically be just a big rock? Would it be anything at all?

So far, the answers are pretty informative.

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More questions:

Is it really possible for a black hole to have a habitable zone like in the movie Interstellar?

Can a neutron star have a habitable zone?

Edited June 11, 2016 by JMBuilder

[YNM]

On 6/10/2016 at 10:59 AM, JMBuilder said:

1. What does a completely dead white dwarf look like? Is it like a solid planet?

2. Are neutron star "fragments" a real thing? Can the "fragments" continue to sustain their reactions?

3. How big would a neutron star with the mass of an average-size planet be?

4. Do bigger stars have bigger habitable zones?

5. Say you had a binary-ish star system consisting of a massive star and a relatively low-mass star. Is it possible to have planets stably orbiting the massive star further out than the lower-mass star?

8 hours ago, JMBuilder said:

By "dead white dwarf," I mean the remnant of a white dwarf after it has completely cooled down. Would it basically be just a big rock? Would it be anything at all?

So far, the answers are pretty informative.

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More questions:

(6.) Is it really possible for a black hole to have a habitable zone like in the movie Interstellar?

(7.) Can a neutron star have a habitable zone?

1. Probably. Nobody knows. We haven't even spot one going dimmer over the years.

2. Fragments... If a neutron star were to hypothetically fragment off, then what the fragments will be depends on their bulk mass. Or so I guess, it could also instantly explodes off. It really depends on what happens in the meantime - these stars, while gravitationally and degenerately "stable", required a lot of energy to compress (hence why there's still the supernova, the remnant star (neutron star or black hole) are only from the core). All other part of the exploding star were required to compress them !

3. Already answered above.

4. Classically (ie. only taking into account bolometric EM radiation and using the standard between 100 - (-15) deg C for life), yes. But not realistically. Bigger stars tends to emit more particle radiation, or emits very high-energy photons. "Bigger" is actually a bit confusing - do you mean more mass (like, class O/B/A/F main sequence star) or radius (which will include things like Red Giant Sun) ? The former makes a lot of UV radiation, the latter makes a lot of particle radiation - not good in any way. Not to mention they die out fast.

5. Classically, yes. Realistically, should be yes too. But I don't know the details.

6. Interesting question. I've wondered for long too.

IMHO it probably can. As long as the accretion disk is "live", then you can. But of course these accretion disk requires "food", so probably the area around it will be very, very hostile to life.

Definitive answer ? Could somebody answer (least, research) better than me ?

7. No ? They only emit things higher than UV light and/or radio wavelength... While there can exist visual or IR radiation the other radiations will render the whole area unsuitable for life.

Edited June 12, 2016 by YNM

[cubinator]

7. Well, a neutron star is basically an object that didn't get *quite* dense enough to become a black hole. As such, it could have an accretion disk that would be at least warm, but unlikely to be habitable.

[JMBuilder]

Yet another question... 

Once again involving the high-mass star and low-mass star binary system, what effect would binary stars like that have on the system's habitable zone if the two stars were orbiting relatively close to each other? Would the zone be even narrower? Would it be wider?

[cantab]

What does a completely dead white dwarf look like? Is it like a solid planet?

So we're talking about a white dwarf (or black dwarf) that no longer emits light, it's only visible by the light it reflects. Some things we do know. It would be a virtually featureless spheroid with no significant terrain. But beyond that is some speculative. But I think the surface will be a mixture of diamond, dry ice, and/or solid oxygen. All these are light coloured, so I think a "black dwarf" would actually be white in reflected light. It will be surrounded by a hydrogen and helium atmosphere.

If the black dwarf is very cold, which it will be if it's lost all internal heat and is far from any stars, that atmosphere will condense out. I wonder if the result wouldn't be a solid hydrogen crust, covered in a layer of superfluid helium. If so, then despite the strong gravity that layer may well shimmer and ripple.