# Thread: Cold Jupiter sized interstella objects

1. How far away could we detect a very cold object the size of Jupiter?

If objects could form slowly from interstellar gas & dust over billions of years they would never get as hot as objects formed in dense stellar nurseries or in the disks around stars.
There must be all kind of objects out there that escape from stellar systems & then very slowly gather mass from dust but never building any heat.

I am trying to find an upper limit to how much matter could hide in the massive volume of space between the stars.

2.

3. Originally Posted by PetTastic
How far away could we detect a very cold object the size of Jupiter?

If objects could form slowly from interstellar gas & dust over billions of years they would never get as hot as objects formed in dense stellar nurseries or in the disks around stars.
There must be all kind of objects out there that escape from stellar systems & then very slowly gather mass from dust but never building any heat.

I am trying to find an upper limit to how much matter could hide in the massive volume of space between the stars.
Any object made of gas and dust that is compressed enough gets warmer just by thermodynamical processes. Stars are formed from an object that we call a protostar. They contract slowly at an increasing temperature until the core temperature and pressure is high enough to start nuclear fusion. So even objects that are not (yet) stars, can have temperatures of several thousand degrees.

Even Jupiter was once much hotter than it is now. It has been cooling down since then.

There is a physical limit of mass that can collapse to form a compact object (Jeans criterion). So, in order to be able to form a Jupiter mass object from collapse and accretion, you would have to find environments, where the necessary conditions are met.

Apart from such hypothetical objects, we know that there is a lot of gas surrounding galaxies - mostly hydrogen. But it is difficult to detect, because it is not very dense and it is in its atomic form. Because of the lack of a electric dipole, we can only detect it in the 21 cm spin flip spectral line.

There have be statistical investigations that try to estimate the total mass of the more massive cooled and dark white dwarves. If you want to find a solution for the riddle of the galactic rotation curves, I can already tell you that at least this idea did not work out.

4. The speed of formation should have a very big impact on temperature, due to the sum of quite a few effects.
• An object forming in a low density cloud can more easily radiate heat out through the cloud.
There is a longer time period for the heat to be radiated away while it is still small.
The colder the object the larger convection currents are bringing heat from impacts out to the surface.
For large-scale objects; a thinner accretion associated with slow formation can have a huge surface area to volume ratio.

The Oort cloud does show that objects have formed nearly a lightyear from the sun.

I do agree, even with the massive volume of space between the stars the upper limit on cold normal matter is small.

The cold hydrogen idea also has its problems if it existed in the amounts required it would refract light and also glow when hit by cosmic rays.

5. If these cold Jupiter objects exist we should soon know.
It looks like some of their bigger cousins have been found.

http://www.nasa.gov/mission_pages/sp...r20100624.html[/url]

6. It has been said that the solar system had a cold formation (as in the sun ignited late) because had it been burning at the time, it's (then powerful) solar wind would not have allowed a gas giant as big as Jupiter to form so close in.

I read the other day that it is now believed that the solar system took maybe 100,000,000 years to form instead of the earlier 30,000,000 years.

7. Something that I have thought about a few times is that the solar wind could not just blow the gas away in an instant.
It seems hard to except that the star stopped growing & then sometime later the solar wind started.

I like the idea the solar wind is what stopped the sun growing.
So the sun was still growing embedded in the disk when it started. You can then imagine the first signs of the solar wind being jets escaping at the poles. Then it would need to stop the infall of gas & dust at the suns equator before it could blow out into the plane of the planets.

I think there is a chance that the solar wind took millions of years to push the still in falling gas back out into space. The expanding heliopause could take the form of a dense ring of gas moving outward.
One of my Pet theories is that Jupiter & co could have formed from this ring.

8. Originally Posted by PetTastic
Something that I have thought about a few times is that the solar wind could not just blow the gas away in an instant.
It seems hard to except that the star stopped growing & then sometime later the solar wind started.

I like the idea the solar wind is what stopped the sun growing.
So the sun was still growing embedded in the disk when it started. You can then imagine the first signs of the solar wind being jets escaping at the poles. Then it would need to stop the infall of gas & dust at the suns equator before it could blow out into the plane of the planets.

I think there is a chance that the solar wind took millions of years to push the still in falling gas back out into space. The expanding heliopause could take the form of a dense ring of gas moving outward.
One of my Pet theories is that Jupiter & co could have formed from this ring.
There is lot of correct reasoning involved. It is true that the moment a star starts the fusion process, its stellar wind can stop the accretion process preventing it from further growth. This is mainly correct for relatively low mass stars, but not for high mass stars, because in this case, you would not be able to form stars beyond stellar masses of about 8 solar masses. Recent 3D model calculations show that the circumstellar disc reduces the radiative pressure along the equator, so that the accretion process can continue, even though the star already ignited its fusion. The main reason for this is that the intense radiation is absorbed at inner radii of the disc and then re-radiated as IR radiation in all directions, especially perpendicular to the disc plane. Most of the wind is diverted along polar regions (flashlight effect).

With stars like the sun, the heating of the inner disc radii is less important, because these stars are cooler and radiate more IR light that can penetrate the disc into larger radii. But it could also just be a coincidence, because pre-stellar evolution of high mass stars is much shorter than for low mass stars like the sun. So, the accretion process already essentially stops before the pre-stellar object (protostar) evolves into a real star with hydrogen fusion. There is a phase of slow contraction of the protostar without mass accretion until the core temperatures rise high enough to support stable hydrogen burning. So, at least the inner region of the circumstellar disc is already depleted before the strong stellar/solar wind sets in. This scenario is most probably also true for the sun.

The jets have nothing to do with stellar wind. Although there is still a lot to learn about jet formation, it seems clear that jets do not originate from the protostar, but from the disc. There are also disc winds that are produced by surface heating from the evolving protostar. The stellar wind is produced by the star itself as soon as nuclear fusion has set in.

Planet formation already sets in during the formation of the star. So, planets should be more common around low mass stars than around high mass stars, because there is more time to form planetesimals before the stellar wind blows the gas and dust away. We observe these disrupting circumstellar discs around young high mass stars, and also around other stars that are in the vicinity of high mass stars.

The rings around Saturn and Jupiter are the result of tidally disrupted asteroids and moons. There is a similar phenomenon in the phase after the stellar accretion onto the protostar has stopped. We find circumstellar discs that are not primordial anymore, but are the result of interactions between rocks and planetesimals inside the planet forming disc, what we call debris discs. They clearly show a different grain size distribution than protostellar accretion discs. Although the gas planets may have formed by accreting gas onto a rocky core, the rings are not the remainders of this process.

9. you would not be able to form stars beyond stellar masses of about 8 solar masses
(basically you can form big stars by doing it slowly & keeping the temperature down delaying the start of fusion)

When thinking about big stars, I always get stuck at this point:

Fusion starts driving convection currents in the star.
Convection currents amplify the magnetic field up to full star strength.
The magnetic field drives the solar wind.

But even if the star swells up a bit when fusion starts, it will be still be rotating at a different speed to the disk.
So the stars magnetic field will get very highly contorted at the point where the rotation speed changes fastest. This would produce an extremely hot excited layer between the star and infalling gas.
It is difficult to see how a big stars can continue to form, but they do exist.

10. Originally Posted by PetTastic
you would not be able to form stars beyond stellar masses of about 8 solar masses
(basically you can form big stars by doing it slowly & keeping the temperature down delaying the start of fusion)
No, you can't. There is no way of doing it slowly. Gravitation cannot be avoided. As soon as a certain amount of matter has accreted on the protostar, the pressure and the temperature in the core is so high that the fusion ignites. The protostar is at that stage so dense that the heat cannot be efficiently radiated away by IR radiation. The protostar simply heats up. There is no way around it. And high mass stars evolve much quicker than low mass stars. While low mass stars are still in their protostellar phase, some high mass stars are already close to their final stage.

In order to form high mass stars (i.e. beyond 8 solar masses), the main process that allows it is the anisotropic radiation field due to the explained influence from the disc.
Originally Posted by PetTastic
When thinking about big stars, I always get stuck at this point:

Fusion starts driving convection currents in the star.
Convection currents amplify the magnetic field up to full star strength.
The magnetic field drives the solar wind.
Protostars are already fully convective. In contrast, the fusion produces an inner radiative zone in low mass stars. High mass stars have an inner convective zone, while the outer layers are purely radiative.
Originally Posted by PetTastic
But even if the star swells up a bit when fusion starts, it will be still be rotating at a different speed to the disk.
So the stars magnetic field will get very highly contorted at the point where the rotation speed changes fastest. This would produce an extremely hot excited layer between the star and infalling gas.
I am not sure that this is true. Do you have any reference for this? The magnetic field does not only reside in the star, but also penetrates the disc and envelope. If anything, the interaction should support magnetic breaking.

11. No, you can't. There is no way of doing it slowly. Gravitation cannot be avoided.
The rate of growth is dependant on cloud density.
Surface temperature depends on rates of heat loss vs heat coming from infalling gas.
Core temperature is dependant on the original temperature of matter that was crushed down into it.

http://www.nasa.gov/mission_pages/sp...r20100624.html
An article on very cold brown dwarf stars that have been found.
Most computer models predicted they should exist.
As cold brown dwarfs have no solar wind, in theory they should still be very slowly growing.

My knowledge is a bit out of date, years back I was supporting simulation & graphics libraries used in this area. In practice that ment debugging user simulations & sometimes the user's physics.

12. Originally Posted by PetTastic
No, you can't. There is no way of doing it slowly. Gravitation cannot be avoided.
The rate of growth is dependant on cloud density.
Initially, yes. But you need a critical density, before the growth can start in the first place. The accretion rate is time dependent. But stellar models show that the evolution time from the protostellar phase until the star starts the fusion process only depends on the mass of the final star.
Originally Posted by PetTastic
Surface temperature depends on rates of heat loss vs heat coming from infalling gas.
Surface temperature of what? The fully developed star? This only depends on its mass. Of the protostar? This depends on its mass and evolutionary stage. Young protostars have temperatures of down to 10 K, when they are still deeply embedded in their natal core. The temperature rises as soon as they become optically thick for IR radiation. Then they evolve up to so called T Tauri stars that can have surface temperatures of several thousand degrees even without nuclear fusion.
Originally Posted by PetTastic
Core temperature is dependant on the original temperature of matter that was crushed down into it.
What core? The one that evolves into a star? Or the core of the final star? Either way, it is not true. All molecular clouds have essentially the same temperature, because they are heated by the interstellar radiation field. The temperature of individual prestellar cores depends on the equilibrium of heating due to gravitational compression plus accretion and cooling by radiation of dust grains (is a function of density, i.e. evolutionary stage during the protostellar collapse) and atomic and molecular excitation.
Originally Posted by PetTastic
As cold brown dwarfs have no solar wind, in theory they should still be very slowly growing.
Stellar wind is existent for fully developed stars. They do not grow anymore. The only exception is the high mass stars that reach the critical core temperature already while they are still accreting material.

13. The real test of any of this is what telescopes like the Spitzer satellite find.

Initially, yes. But you need a critical density, before the growth can start in the first place.
The probability that any stars other than the first generation in the galaxy, formed from hydrogen gas reaching critical density is very low. The presence of any seed object reduces the gas density required greatly, reaching near zero for planet sized seeds.

I find the models that show, dust collapsing into filaments, then sections of the filaments collapsing into seed objects, that then accrete gas are fairly believable.
Anyway a cloud big enough to get hydrogen to critical density would be so large that the probability of it containing no rocky seed objects is very low.

The protostar is at that stage so dense that the heat cannot be efficiently radiated away by IR radiation.
This assumes a fast forming object totally embedded in its disk. A slow forming object could have a much thinner disk maybe looking more like Saturn's rings.

Stellar wind is existent for fully developed stars
The brown dwarf objects that Spitzer saw were as cold as 450 Kelvin so more like big versions of Jupiter. Therefore they would have no solar wind & being in interstellar space could still be attracting gas & dust.

Until we got a telescope as cold as the Spitzer in space the only stellar objects we could see forming was the hot ones. Now it will be interesting to see if objects can form cold or the Spitzer objects formed hot & are tens of billions of years old.

14. How can you say that space is massive? Our solar system may be huge, and it may be all there is to space. We have no solid evidence on how "infinitely big" the 'universe' is. For all we know, matter and time just-stops. At an edge.

15. Only a quick response this time. Maybe more later.
Originally Posted by PetTastic
The probability that any stars other than the first generation in the galaxy, formed from hydrogen gas reaching critical density is very low. The presence of any seed object reduces the gas density required greatly, reaching near zero for planet sized seeds.
I wasn't talking about population III stars, i.e. primordial stars that must have formed out of hydrogen alone. None really knows, how this was possible. Contemporary star formation needs hydrogen, other trace gases and some dust. This is necessary to provide cooling. Cooling is necessary to avoid heating of the forming prestellar core for a while, whose temperature simply increases due to fundamental thermodynamics. If the core heats up too quickly, a dense object like a protostar would never form. The criterion to start gravitational collapse still exists. Trace gases are mainly CO (carbon monoxide), the dust consists of sub-micrometer sized grains of silicates and graphite that grow during the star formation process. There are never planetesimals or rock sized particles involved. These seeds are only needed for planet formation from the circumstellar disc.
Originally Posted by PetTastic
I find the models that show, dust collapsing into filaments, then sections of the filaments collapsing into seed objects, that then accrete gas are fairly believable.
Yes, this scenario is correct. These seeds are called prestellar cores, but they are not solid objects. They consist of dense entities of gas and dust.
Originally Posted by PetTastic
The protostar is at that stage so dense that the heat cannot be efficiently radiated away by IR radiation.
This assumes a fast forming object totally embedded in its disk. A slow forming object could have a much thinner disk maybe looking more like Saturn's rings.
No.
Originally Posted by PetTastic
The brown dwarf objects that Spitzer saw were as cold as 450 Kelvin so more like big versions of Jupiter. Therefore they would have no solar wind & being in interstellar space could still be attracting gas & dust.
How brown dwarves form is still a subject of current research. Currently it seems that there a several scenarios that are able to produce them. But generally, their basic formation process is no different from the formation of other stars. They can also form from gravitational collapse, although they are less dense so that the core temperatures are too low to ignite fusion processes. Don't confuse the effective temperature of a star with its core temperature.
Originally Posted by PetTastic
Until we got a telescope as cold as the Spitzer in space the only stellar objects we could see forming was the hot ones. Now it will be interesting to see if objects can form cold or the Spitzer objects formed hot & are tens of billions of years old.
No. Spitzer, and currently Herschel, are phantastic tools, but cold objects have been observed from ground for decades using millimetre and submillimetre telescopes. In addition, Spitzer was not the first infrared space telescope. There were IRAS and ISO.

16. The famed Voltaire was possibly misunderstood by many and criticised by some. In that regard you may be similar.
Originally Posted by Voltaire
How can you say that space is massive?
Poor choice of words. Massive implies mass, i.e. matter, whereas what you seem to be talking of here is the 'siae' of space.

Originally Posted by Voltaire
Our solar system may be huge, .
No it isn't. It is tiny, miniscule, insignificant, unbelievably small.

Originally Posted by Voltaire
......and it may be all there is to space.
Do you have anything at all, apart from a third rate education, with which to substantiate this claim. The only way I can see this would be true is if we are a computer simulation. Is that what you are suggesting? Please feel free to embarrass me with an elegant, logical alternative.

Originally Posted by Voltaire
For all we know, matter and time just-stops. At an edge.
Is the edge guarded by fluffy bunny rabbits?

Welcome to the forum, by the way.

17. Aah, the refreshing Ophiolite. I hope, Voltaire, you don't get intimidated. And I hope, Ophiolite, you don't take offence from my remarks. While others try to use a rapier to lay open the errors of other forum members, he frequently uses the axe. But he is usually right. Just like in this case.

Also welcome from my side, Voltaire, and I hope you are here to learn. There are many skilled and experienced people on this forum. And I can tell you that you are completely wrong. The solar system has a diameter of about 100 AU only counting planets and TNOs/KBOs. If you include the hypothetical Oort cloud, it increases to several thousand AU. This is still much smaller than the distance to the nearest stars (several parsecs, 1 pc = 206265 AU), let alone the size of the Milky Way (diameter several dozen kiloparsecs). It is also well established that the closest other galaxies like the Andromeda galaxy are several million parsecs away.

We have already discussed in many threads that there is no edge of the universe, just like there is no centre. Do you believe that the Earth is in the centre of the universe?

But don't let this thread derail, because it is about the formation of planet sized objects, and not about the nature of the universe. If you want to discuss this, please open a new thread. Thank you.

18. Originally Posted by Dishmaster
And I hope, Ophiolite, you don't take offence from my remarks.
The day I take offence at a well intentioned, accurate statement I would lose all moral right to castigate young (and old) offenders with my double edged, diamond coated axe. :wink:

I've been very nice to Voltaire on another thread where he was being quite inventive.

19. Looking at my notes on some of the old models that were trying to predict what IRAS would see in 1981.
Jupiter as it was 4 billion years ago.
5 x current radius (equator, half the size of the sun)
Density less than 0.2 g/cm³
Gravity at cloud tops 0.2 g
1500K surface temperature.
Energy output 120 x current output.
Disk diameter 2,000,000 km.
Disk 500 km thick at planet.
Infalling gas delivering 3 MJ per gram to disk.

Sounds like a fun object!
Do these numbers sound ok?

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