For Questions That Don't Merit Their Own Thread

[K^2]

To a stellar evolution astronomer, metals are anything that's not hydrogen or Helium. A high metallicity star can have a lot of elements that are lighter than Earth's core on average. So no, I don't think metallicity is necessarily an indicator of heavier terrestrial worlds, but there could be factors leading to a correlation between the two.

On the other hand, I would absolutely expect the metallicity of the star to be correlated to the number of rocky planets in the system. If a star system formed from just a hydrogen gas cloud, I expect it to have just the star and maybe a few gas giant. To form rocky worlds, you have to have remnants of past supernovae mixed in, and that ought to add to the star's metallicity. I just don't know how much of a correlation you'll get if you just plot one against the other.

[DDE]

Bouncing off of that question, is it possible that there was an early population of pure non-metal planets alongside the earliest generation of stars?

Edited January 29, 2022 by DDE

[Gargamel]

48 minutes ago, DDE said:

Bouncing off of that question, is it possible that there was an early population of pure non-metal planets alongside the earliest generation of stars?

Well those would just be gas giants, right? 

[DDE]

56 minutes ago, Gargamel said:

Well those would just be gas giants, right? 

Good question. I believe the textbook explanation is that there's a rocky core beneath the metallic hulydrogen, which would be the original planetsimal that collected the hydrogen around itself. Not sure if the heterogeneities of a metal-deficient accretion disc would suffice to form planets.

[kerbiloid]

https://en.wikipedia.org/wiki/Super-Jupiter

(Cuz the first generation of stars were supergiants of tens solar masses, so the junk heap around them was same giantish.)

Edited January 29, 2022 by kerbiloid

[Terwin]

1 hour ago, DDE said:

Good question. I believe the textbook explanation is that there's a rocky core beneath the metallic hulydrogen, which would be the original planetsimal that collected the hydrogen around itself. Not sure if the heterogeneities of a metal-deficient accretion disc would suffice to form planets.

As we have binary(and trinary) star systems, and the only required difference between a star and a gas giant is the total mass(ie heavy enough to maintain fusion), I see no reason an early star system could not have one or more gas giants(aka brown-dwarf stars which are not the system primary)

[JoeSchmuckatelli]

6 hours ago, DDE said:

Bouncing off of that question, is it possible that there was an early population of pure non-metal planets alongside the earliest generation of stars?

I think I remember reading speculation by a researcher that light first generation 'failed stars' (gas giants) could have been present... But they're anticipated not found.  The gas giants around nowadays are expected to have dense cores - but it took early stars exploding to seed the heavier elements. 

https://academic.oup.com/mnras/article/422/1/215/1020516

(not exactly on point, but quite interesting) 

I wonder if / whether any of those early planets survived (recently discovered 'rogue stars' being ejected from galaxies could support a population of rogue first generation gas planet wandering around between galaxies idea) 

One of the things I remember reading about 18 Sco was that it was dusty, making observations difficult.  It's expected to be a higher metallicity star than Sol, so that coincides with what @K^2writes (my memory is 'rocky' not 'gassy' w/r/t the dust mentioned. 

Edited January 29, 2022 by JoeSchmuckatelli

[JoeSchmuckatelli]

Oh - and back at @K^2-I appreciate the reminder that 'metallicity' =/= metals (easy to forget for non astronomers).

I'm speculating, however, that if you take a star and system like Sol's as a baseline and find a higher metallicity star that it's whole birth and formation environment likely averaged more of the heavier chemical elements.  Is that a fair assumption? 

I know we are sparse on direct observation of rocky exoplanets - I'm just wondering if the theory suggests that rocky planets in such a place would be denser, or if that's one assumption too far? 

[magnemoe]

26 minutes ago, JoeSchmuckatelli said:

I think I remember reading speculation by a researcher that light first generation 'failed stars' (gas giants) could have been present... But they're anticipated not found.  The gas giants around nowadays are expected to have dense cores - but it took early stars exploding to seed the heavier elements. 

https://academic.oup.com/mnras/article/422/1/215/1020516

(not exactly on point, but quite interesting) 

I wonder if / whether any of those early planets survived (recently discovered 'rogue stars' being ejected from galaxies could support a population of rogue first generation gas planet wandering around between galaxies idea) 

One of the things I remember reading about 18 Sco was that it was dusty, making observations difficult.  It's expected to be a higher metallicity star than Sol, so that coincides with what @K^2writes (my memory is 'rocky' not 'gassy' w/r/t the dust mentioned. 

Decent chance large stars was more common back then, much more gas cloud and no metallic cores as aggregates and no supernova compression shocks. 
You don't need to get that much smaller than the sun to get an star who will last over 13 billion years but very old stars are rare so the first was huge and short lived, creating the current universe. 
 

[JoeSchmuckatelli]

1 hour ago, magnemoe said:

no supernova compression shocks.

...well, now you forced me to google Pop.3 supernova:

The Universe's First Supernovae May Have Been Powerful, Asymmetric Jets - ExtremeTech

very interesting!

[Jacke]

With low metallicity, the Jeans Mass, the minimum mass of a particular interstellar gas cloud that will collapse, goes up.  The metallicity effect is not mentioned directly in this article:

https://en.wikipedia.org/wiki/Jeans_instability

but I remember it well from long ago astrophysics courses.  This would affect both stars and their planetesimals which form whatever planets they have.  Also, as gas clouds collapses, the Jeans Mass drops, so clouds will fragment, causing multiple stars and planetesimals to form.

[K^2]

19 hours ago, DDE said:

Good question. I believe the textbook explanation is that there's a rocky core beneath the metallic hulydrogen, which would be the original planetsimal that collected the hydrogen around itself. Not sure if the heterogeneities of a metal-deficient accretion disc would suffice to form planets.

In the Solar System, yeah. The heavier materials will form a core and collect lighter materials. It's almost like a nucleation site. But you can definitely get at least brown dwarves from just hydrogen. It's hard to say without running simulations how small the smallest gas giants would be if they have no rocky core, but given that the highest estimates of the Jupiter's icy/rocky portion of the core's mass is a little over 10% of the total mass, it sounds like something of that size could have formed and survived ignition even without a core of heavy elements. So my guess would still be that yes, some of the earliest proto-stars could have had some pure hydrogen gas giants orbiting them.

But if anyone wants to take the time to do a literature search to see if anyone has actually done simulations, I'd be very curious to see the results.

[kerbiloid]

Sleeping whales.

Spoiler

 

 

Isn't 'Oumuamua?

Edited January 30, 2022 by kerbiloid

[StrandedonEarth]

6 hours ago, kerbiloid said:

Sleeping whales.

  Hide contents

 

 

Isn't 'Oumuamua?

I was thinking the same thing. Needs to be a sperm whale though

[JoeSchmuckatelli]

If I were kicking it out in the Asteroid Belt and had LOS on the Orion constellation - but the sun was between me and it - could I still make out the constellation? 

(I know the sun will be the brightest thing I can see, but without atmosphere to create glare, will the stars beyond be visible? 

[JoeSchmuckatelli]

Associated question: could we put an observatory at the Martian L5 and use the sun for gravitational lensing? 

[Gargamel]

2 minutes ago, JoeSchmuckatelli said:

Associated question: could we put an observatory at the Martian L5 and use the sun for gravitational lensing? 

I’d like to be corrected on this if I’m wrong, but my gut reaction is that it’s too close and not massive enough to be an effective magnifier for the purpose described.   That and blocking out the sun would reveal the corona which might more than negate any advantage it might impart.  

[SOXBLOX]

1 hour ago, JoeSchmuckatelli said:

Associated question: could we put an observatory at the Martian L5 and use the sun for gravitational lensing? 

Nah. The focus of the solar gravitational lens is waaay out there, on the very farthest edge of the solar system. The Wikipedia page says the focal point is at 542 AU, which is 360-something times the orbit of Mars. You still get a gravitational lensing effect at Mars, you just can't really use it for imaging things. It's like looking through a pair of glasses sideways.

[monophonic]

2 hours ago, JoeSchmuckatelli said:

If I were kicking it out in the Asteroid Belt and had LOS on the Orion constellation - but the sun was between me and it - could I still make out the constellation? 

(I know the sun will be the brightest thing I can see, but without atmosphere to create glare, will the stars beyond be visible? 

Assuming the Sun does not glare them out within whatever optics (incl. Mk1 Eyeball) you are using, they should be visible. Block the Sun behind a disc or edge of the window or whatever and you should see the stars just fine.

[kerbiloid]

2 hours ago, JoeSchmuckatelli said:

Martian L5 and use the sun for gravitational lensing? 

No, because the Son lensing distance is at 550 (from another source, 650) AU from the Sun.

[kerbiloid]

1. The Shuttle was able to lift 29.5 t.

2. The Shuttle was able to return 14.5 t.

3. The Shuttle didn't have any flight abort option but separating and gliding to a runway.

How can the Shuttle land with the 29.5 t heavy cargo on flight abort, when it was able to land just 14.5 t?

(The abort modes included both atmospheric and suborbital options).

[JoeSchmuckatelli]

 a loop-de-loop with the hatches open? 

[Hyperspace Industries]

Since water rockets lose pressure (and therefore thrust) as water (and therefore mass) is shot out the back, could you be able to tune a water rocket to have a constant thrust to weight ratio? What would you need to tune?

[lrd.Helmet]

2 hours ago, kerbiloid said:

1. The Shuttle was able to lift 29.5 t.

2. The Shuttle was able to return 14.5 t.

3. The Shuttle didn't have any flight abort option but separating and gliding to a runway.

How can the Shuttle land with the 29.5 t heavy cargo on flight abort, when it was able to land just 14.5 t?

(The abort modes included both atmospheric and suborbital options).

For a trip to the ISS it could bring around 15 t. So I guess they had the capability to bring more to LEO, but they never intended to use it for that. 

[kerbiloid]

15 minutes ago, lrd.Helmet said:

For a trip to the ISS it could bring around 15 t. So I guess they had the capability to bring more to LEO, but they never intended to use it for that. 

It was built by 1985, long before the ISS, and even before the idea that Mir-2 and Freedom projects can be united.

And it was developed as a replacement for all existing launch vehicles, to fly every two weeks.

So, 29.5 t were for reasons.