# Giant exoplanet orbits smaller dwarf star



## Brian G Turner (Nov 2, 2017)

Interesting piece challenging our notion of solar system formation/stability: Giant 'monster planet' is orbiting a tiny sun and it's got astronomers baffled

Strangely, I'm struggling to find an original science source for this story on NTGS-1b. I'll see if another one comes up later.


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## BigBadBob141 (Feb 26, 2018)

I don't see what the problem is.
Even if the star is half the size of our sun it would still be vast compared to a planet th size of Jupiter.


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## Brian G Turner (Feb 26, 2018)

Here's a direct link to the NGTS telescope site announcement:
Different duo - Dwarf star and giant planet

The suggestion appears to be that existing ideas of planetary system formation cannot account for such a pairing.


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## Ursa major (Feb 26, 2018)

I had to laugh at the Mirror headline: 'Giant "monster planet"...'

Does this mean that Jupiter is also a giant monster planet...?


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## LordOfWizards (Feb 26, 2018)

Ursa major said:


> I had to laugh at the Mirror headline: 'Giant "monster planet"...'
> 
> Does this mean that Jupiter is also a giant monster planet...?



Agreed. The article states that this "monster planet" is about the size of Jupiter. I don't get what the confusion is either. I read through the article, and all they say is "Standard theories state that when a star is formed, only a certain percentage of mass is available for accompanying planets". I'd like to know more about this "Standard Theory" they refer to. There are a myriad of explanations that could be found, including the 'capture' of a rogue planet from another system. Another thought I had was dwarf stars are sometimes the result of what is left over from a red giant. If the system had been there awhile, the star may have expanded and lost mass, etc.

It reminds me of a quote from Max Planck: "A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it." 

And, yes Ursa. We'd best keep an eye on Jupiter, as it might try to eat us when we're not looking.


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## Brian G Turner (Feb 26, 2018)

LordOfWizards said:


> There are a myriad of explanations that could be found, including the 'capture' of a rogue planet from another system.



Ssshh! They don't seem to have caught up with that possibility yet.


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## J Riff (Feb 26, 2018)

Can anyone actually 'see' any planets yet? No, but, they supposedly know what's going on out there with all the trillion or so projected planets in this galaxy alone? A huge star, with small planets round it, would be even more unusual, wouldn't it? Shouldn't it just swallow them all up? Well, I'm baffled too. 
 Wait, just wait until people from a monster planet get here someday and start buying real estate. Each home will be the size of the great pyramid at Giza, with a pool and storage shed. And a nice garden, with a little path...* )


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## LordOfWizards (Feb 26, 2018)

@J Riff, If you look in the article, they mention the *N*ext-*G*eneration *T*ransit *S*urvey (NGTS) Which is an array of high powered telescopes in the Andes. The name suggests to me that they are using a kind of transit detection, which means they measure the light of relatively nearby stars, and watch for a very slight dimming of the starlight. It can only be detected by computer, but it is assumed that the planet is 'transiting" in front of the star, and they calculate the size based on the amount of dimming. 

Hopefully by the time the giants get here, we'll be gone.


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## J Riff (Feb 27, 2018)

I know, I know... it's there all right. Giants are probably there as well. Giant ants, teeny tiny people, who knows? We have to wait for tourism to expand a bit.


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## BAYLOR (Feb 27, 2018)

Brian G Turner said:


> Interesting piece challenging our notion of solar system formation/stability: Giant 'monster planet' is orbiting a tiny sun and it's got astronomers baffled
> 
> Strangely, I'm struggling to find an original science source for this story on NTGS-1b. I'll see if another one comes up later.



Is there any chance that this gas giant might simply be a wandering planet that was captured by the stars gravity?


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## LordOfWizards (Feb 27, 2018)

BAYLOR said:


> Is there any chance that this gas giant might simply be a wandering planet that was captured by the stars gravity?



I wonder if it's coincidence you used the word "wandering" since the original word planet comes from the ancient Greek word _planete_, which meant "wanderer".

I believe it was used because very early astronomers noticed stars that moved over time with respect to the fixed star field behind them; It turns out they were not stars at all, but planets in our system. Telescopes back then were nothing more than a crude lens at the end of a small tube made of wood or leather.


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## J Riff (Mar 5, 2018)

But planets will never move away from their home stars? From what I understand, it's almost impossible for planets or stars to move much closer to, or further away from, from the galactic core that everything rotates around. Even a star exploding would not send planets flying off to join other solar systems. The whole mess would just stay where it is in relation to the big black hole or whatever it is hiding in the centre of this milky galaxy. So they say. That's why whatever exploded here in this solar system, is still coming round and hitting the Earth, rather than booting it off for, say, Proxima C or the Pleides. Gravity is apparently serious about this mass-attracts-mass business, it's not my idea. * )


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## Brian G Turner (Mar 5, 2018)

J Riff said:


> But planets will never move away from their home stars?



A class of exoplanets known as "Hot Jupiters" orbit very close to their stars - existing models of planetary formation say that could only happen if the planet had slowly spiraled in. But if it had, then it would have disturbed any existing planets and moons in lower orbits, and effectively slingshot them out of the star system.

As Hot Jupiters have proven to be very common, then this suggests there should be a number of planets and moons which have been forced from their original star systems.

Additionally, re-modeling of the formation of our own solar system suggests it was a very chaotic and violent place - best imagined as something like a game of billiards, where even Jupiter and Saturn might have originally been in closer orbit to the Sun. One particularly successful model even requires another gas giant to have formed in the solar system, only to have been flung out into interstellar space through interactions with existing planets.

So there are just a couple of reasons why it's increasingly believed that there must be a significant number of wandering planets moving through space - and why it makes sense that some of these may be captured by other stars.


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## Venusian Broon (Mar 5, 2018)

Brian G Turner said:


> So there are just a couple of reasons why it's increasingly believed that there must be a significant number of wandering planets moving through space - and why it makes sense that some of these may be captured by other stars.



I can't find the article that talks about it, but from modelling of solar system formation and evolution, some think that there are probably more planets out in interstellar space - 'Rogue Planets' - than there are in orbit around stars. This was backed up by the discovery of some potential candidates a few years ago. Modern estimates of Jupiter-sized rogue planets give supposedly their number at about 0.25 times the number of stars in the galaxy. Of course then, you have to add 'Earth-sized' and smaller planets? (Surely, as they are lower mass and assuming that astronomical objects fits some reasonable power law - don't see why not - there must be much more of them.) As you've stated, Brian, I do think that a great deal of these rogue planets were indeed formed in solar systems but then wrenched out by processes - some of which you mention.

Unfortunately for any idea that a rogue planet might have been gravitationally captured by a star system....while it may be possible, as I've said many times before on this topic, SPACE IS VERY BIG . In four billion years the Andromeda galaxy will collide with out galaxy and when these ~1 trillion stars hits our ~300 million...yep, there are expected to be no direct collisions. Similarly for a rogue planet to just hit a star system is going to be extremely rare. Furthermore the planet must move with a velocity very close to that of its capturer. Also, it must involve a third body (either another planet or star bound to its capturer) to absorb, into its orbit, the orbital energy and angular momentum released by the capture. It all adds up to, 'well the universe is such a big place, so it must have happened _somewhere_, but it's so rare we should not rely on this explanation to explain virtually anything!'

As for this star and planet - the star is described as a red dwarf with a mass half that of our sun, hence it's still main sequence and likely to remain so for many billions of years. So the star should not have lost mass and that cannot be an explanation for said Jupiter sized object to be in it's system.

I believe the standard theory they are referring to is the Solar Nebular Disk Model and my guess is that there probably is a correlation between the mass of the proto-star accretion disk, the mass of star it produces, and how much 'stuff' is left over for planetary formation. In this case it seems said planet has taken a much higher proportion of the 'stuff'. Note however what sort of figures we're dealing with here: Here on Sol, Jupiter is ~0.1% the mass of the Sun. In this system, this big planet is ~0.15% the mass of the red dwarf. Doesn't look much at all!

The problem with all current theories and models of solar system formation is that we've only really had one example to theorise about and measure properly, and it is only in the past few decades that we've been able to start to pick out what other systems do. As each new observation adds to the zoo of star systems perhaps we'll have a better chance at correctly unpicking how solar systems_ can_ form and evolve.


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## Lumens (Mar 5, 2018)

J Riff said:


> But planets will never move away from their home stars?


Yes they will. This happens due to a phenomenon called 'orbital resonance'. Small nudges on every orbit will build up over time to sling even monster planets out of a solar system, or into the sun.


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## night_wrtr (Mar 5, 2018)

Venusian Broon said:


> I can't find the article that talks about it, but from modelling of solar system formation and evolution, some think that there are probably more planets out in interstellar space - 'Rogue Planets' - than there are in orbit around stars.



Maybe this one from 2011?
Lonely Rogue Worlds Surprisingly Outnumber Planets with Suns

BUT, here is an article (2017) that argues against that. 
Rogue Planets: Not as Plentiful as Thought - Sky & Telescope


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## Venusian Broon (Mar 5, 2018)

night_wrtr said:


> Maybe this one from 2011?
> Lonely Rogue Worlds Surprisingly Outnumber Planets with Suns
> 
> BUT, here is an article (2017) that argues against that.
> Rogue Planets: Not as Plentiful as Thought - Sky & Telescope



Yeah they are a bugger to spot, what with no light anywhere near 'em!

I think the 0.25x figure I quote is in line with the 2017 research which comes up with 75 million Rogue Jupiters - I note that it says that's a maximum figure as they may be counting 'Jupiters' that are still bound to their stars. I would still think that we could be talking about hundreds upon hundreds of millions of rogue planets Earth size and smaller out there.


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## J Riff (Mar 6, 2018)

Into their sun yes, out of their big loop around the core, not likely, not for ages. So, nothing much 'wandering' around the galaxy. Even out here in the sticks, everything was locked in millions of years ago. At 67,000 MPH we are stuck around a Sun going 450,000 per, can't see any way of breaking out of that.


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## Venusian Broon (Mar 6, 2018)

J Riff said:


> Into their sun yes, out of their big loop around the core, not likely, not for ages. So, nothing much 'wandering' around the galaxy. Even out here in the sticks, everything was locked in millions of years ago. At 67,000 MPH we are stuck around a Sun going 450,000 per, can't see any way of breaking out of that.



Nope, not at all, physics tells us different. Unless you think Voyager 1 & 2 ain't comfortably cruising into the interstellar space of our galaxy.

You just need to achieve escape velocity from the solar system. And usually, for an object in orbit, one gravity assist from a large object is all you need.

Jupiter has probably been sending enormous numbers of sizeable objects into deep interstellar space for billions of years, causing plenty of galactic wanderers. (In fact the Nice model for our own solar system evolution suggests that Jupiter caused an Ice giant to be ejected from out solar system)

To send an object into inter-_Galactic _space, i.e. outside the milky way, requires a much higher escape velocity (relative to galactic core and mass)...but stars have been observed being forcibly 'chucked' out of the galaxy by natural gravitational interactions of other objects also.


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## J Riff (Mar 6, 2018)

If our Sun blew up, all the wreckage would lump together and keep rotating at the same distance from the galactic core. Nothing would wander off to Proxima, or anywhere else. And, nothing comes here from other solar systems. It's too far. You may start out well, blasted off by a super-nova, but would be attracted back to the main mass of matter comprising this solar system, long before you'd start being attracted to anything else, even if only a few light years away. It would seem that one could head inward, towards the core, but velocity and angular momentum deny this. So, no wandering solar bodies of any kind, not at those speeds. Simple physics. )


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## night_wrtr (Mar 6, 2018)

There are examples of hypervelocity stars that are already on their way out of the galaxy beyond escape velocity.


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## Venusian Broon (Mar 6, 2018)

J Riff said:


> Simple physics.



You don't seem to understand the basic concepts of 'escape velocity', which is the simple physics you need: Escape velocity - Wikipedia

Basically when material attains or goes faster than this velocity it will _never return _to the original massive object. It is not about it being attracted to another massive object as if somehow it can only escape if it 'latches' onto another body. (Anyway, an object that has attained escape velocity for a solar system will still be bound to the galactic core and remain in its influence _anyway_, unless it has also attained the escape velocity for escaping that much bigger object.)

If the sun went Supernova, then you are clearly incorrect. The energy of the explosion would easily accelerate masses of the star well beyond any capture of the original system. i.e. by giving it a velocity well over the escape velocity of the original mass. You can actually observe this today in the Crab Nebula - the still expanding supernova remnant.

As this internet paper states (Expansion of the crab nebula): "_Given that supernovae are highly explosive events, in the absence of some strong retarding force, the resulting supernova remnant should continue to expand uniformly into the surrounding interstellar medium_" So, it will not return to the original point where the star blew up. See - I'm not making it up. 

But there are also other different mechanisms for objects to be ejected from stars' systems by attaining escape velocity. Simple physics.


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## LordOfWizards (Mar 7, 2018)

Lumens said:


> Yes they will. This happens due to a phenomenon called 'orbital resonance'. Small nudges on every orbit will build up over time to sling even monster planets out of a solar system, or into the sun.





Venusian Broon said:


> But there are also other different mechanisms for objects to be ejected from stars' systems by attaining escape velocity. Simple physics.



There are two reasons why I'm reasonably sure that planets can be hurled away from their stars.
1) What Lumens said.
2) Gravity assist.

And I'm reasonably certain that both of these things happen way more frequently early in the formation of a solar/star system. Then you have a ginormous amount of binary systems out there. Eighty percent of them according to this article. Binary systems have more potential than single star systems to throw things around since there can be plenty of "wobble" for lack of a better term. 

The second item is probably the other most common mechanism for hurling planets around. Early in the star system's formation there is a lot of chaos, and orbits are not necessarily even close to being circular (in our system orbits are almost circular. Example: Earth's orbits' eccentricity is only 0.0167) We have already witnessed plenty of those. (Reference: "To date, astronomers have measured the orbital inclinations of 91 exoplanets and more than a third (36) move on orbits that are significantly misaligned, tilted by more than 20 degrees. Nine of them move on retrograde orbits." May 26, 2016 From here.) Two massive planets that closely approach but miss each other can yield a "slingshot" effect due to gravity. Or a planet flung toward it's own star can get gravity assisted from the star. 

And yes, VB, I missed the fact that this was a red dwarf, and therefore still in it's main sequence so it could not be the remnant of a red giant. 

What can be missed is that in this equation: F = (G * m1 * m2) / r^2 because the radius is in the denominator and it is squared, the force of gravity falls off rather quickly, making escape velocity easier to achieve than one might think. Twice the distance = one quarter of the gravitational force. (see graph below) 

Lastly, with regard to the capture of a planet. I understand that due to the vastness of space, the likelihood may be small, but then again we have roughly three billion stars in the Milky Way. The Milky Way is a mere 100,000 light years across, and it is relatively flat. I could show the math, but it would be tortuous for some, so here: The true stellar density near the Sun is estimated as 0.004 stars per cubic light year. 

I looked up rogue planets, and at a minimum, estimates say there are two Jupiter sized planets for every star. Statistically, over billions of years, thats still a lot of chances for planet capture. (given that approach velocities of the crossing paths would need to be nearly perfect). 




 
Escape velocity starts at the surface, but drops off quickly.


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## Venusian Broon (Mar 7, 2018)

LordOfWizards said:


> Lastly, with regard to the capture of a planet. I understand that due to the vastness of space, the likelihood may be small, but then again we have roughly three billion stars in the Milky Way. The Milky Way is a mere 100,000 light years across, and it is relatively flat. I could show the math, but it would be tortuous for some, so here: The true stellar density near the Sun is estimated as 0.004 stars per cubic light year.
> 
> I looked up rogue planets, and at a minimum, estimates say there are two Jupiter sized planets for every star. Statistically, over billions of years, thats still a lot of chances for planet capture. (given that approach velocities of the crossing paths would need to be nearly perfect).



Excellent post LoW, interested in your stats though.

My understanding is that the number of stars in the Milky way is a factor of 10 less - usually given as 300 million, or a range of 200-400 million because it's tricky finding exactly how many dim red dwarfs are actually out there. The 0.004 local star density value is stated explicitly in Wikipedia and corresponds to each star having a 'box' of space approximately 6 light years sided in length. (or if you want curves, a circle of space with a radius of 3.9 light years )

As for the estimates for rogue planets - as @night_wtr pointed out, a more recent, detailed survey using much more data downed this 2x planet per star limit to 0.75x and they stated that it was a high limit, as they there was a fair chance that they were also recording micro lensing from Jupiter-sized planets that were still bound to star systems.

Now it's true that the extent of the gravitationally bound extent of the solar system could be viewed as 1 light year in diameter, so that seems to fill that '6 light year box' reasonably well...but objects so far out (a big band of comet-like objects) are really easy to knock out of the system by perturbation - as escape velocity that far out is tiny.

To correctly estimate chances of planet capture you have to really match velocities, as you've stated and that's the thing I think that makes such capture so unlikely. On top of this also you have to provide a mechanism for the rogue planet to lose any excess angular momentum that it may bring etc. as the chances of it coming in _exactly _as it should to just take it's place in orbit are should be in practical terms zero.

Essentially it means that the rogue planet coming in has to hit a very specific spot, hence extremely tiny, for the velocity that it's carrying, and also interact with a capture mechanism _in situ_ at the correct place that will allow it to be bound. I don't know how one would go about statistically calculating this, but I'm sure this figure for 'normal' situations must be astronomically tiny. Possibly lots of chances of it _perhaps _happening (loads of 'fly-bys'), but virtually no chance of rogue planets actually getting captured. Even given billions of years.

There is one exception - planets should also be able to form on their own in nebula. So if they do so in the vicinity of star systems forming they will have the advantage of being relatively well matched velocity-wise, so they could be potential for more actual capture of rogues in these 'star nurseries'. Also very new planetary discs will be pretty hectic with large numbers of bodies, so again I think there should be more opportunity for these star systems to accommodate outsiders via gravitational mechanics.


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## Brian G Turner (Mar 7, 2018)

Venusian Broon said:


> There is one exception - planets should also be able to form on their own in nebula. So if they do so in the vicinity of star systems forming they will have the advantage of being relatively well matched velocity-wise, so they could be potential for more actual capture of rogues in these 'star nurseries'. Also very new planetary discs will be pretty hectic with large numbers of bodies, so again I think there should be more opportunity for these star systems to accommodate outsiders via gravitational mechanics.



Something else we might add to the discussion is brown dwarfs, which are proving to be surprisingly common - but difficult to detect.

In simple terms, they are somewhere between a gas giant planet and a small star, with the caveat that they don't have enough mass for fusion to take place in their core - which makes them very dim and very difficult to detect.

However, in the past few years we've been able to detect them more easily, including a binary brown dwarf just over 6 light years away - and now the 3rd nearest (detected!) star system to Earth: Luhman 16 - Wikipedia


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## Venusian Broon (Mar 7, 2018)

Brian G Turner said:


> Something else we might add to the discussion is brown dwarfs, which are proving to be surprisingly common - but difficult to detect.



The survey that looked for Rogues (the one giving 0.75x rogues per star in the galaxy, mentioned above) should have picked up brown dwarfs as part of the 'Jupiter-sized objects' (Brown dwarfs should be close in volume/radius to Jupiter), given that they used Gravitational Lensing to make the calculation and I'd guess that the larger the mass, the easier it would be to detect the lensing effect. However, I can't see if they made any comment on that, so perhaps they weren't looking at getting data on brown dwarfs??? I would have to research and read up!

There is actually quite a debate as to if brown dwarfs are common - surveys in 2012 stated that there were surprisingly few - maybe only one brown dwarf for each six main sequence stars: NASA - WISE Finds Few Brown Dwarfs Close To Home.

This is a bit counterintuitive for me, I'd think there should be more brown dwarfs lying about, but apparently in our vicinity it's just not the case!

However one should be careful with such a small sample - another more recent paper: How Many Brown Dwarfs in the Milky Way? suggests a bigger proportion of 2 MS stars to each BD. The other interesting point in this work is that the figure they arrive at is for 'high mass' brown dwarfs, so we still have to add in the BD's that are lower in mass than 0.03 stellar masses and higher than 13 Jupiter masses.

Could be masses of interesting stuff lying out there in the dark .


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## LordOfWizards (Mar 7, 2018)

Venusian Broon said:


> My understanding is that the number of stars in the Milky way is a factor of 10 less - usually given as 300 million, or a range of 200-400 million because it's tricky finding exactly how many dim red dwarfs are actually out ther



Quickly (I'm on my lunch break) This is from Wikipedia: "The Milky Way is a barred spiral galaxy with a diameter between 100,000 and 180,000 light-years. The Milky Way is estimated to contain 100–400 billion stars." Here is the link: Milky Way
But if you ask google directly it says 250 Billion + or - 150 Billion.


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## Venusian Broon (Mar 7, 2018)

LordOfWizards said:


> Quickly (I'm on my lunch break) This is from Wikipedia: "The Milky Way is a barred spiral galaxy with a diameter between 100,000 and 180,000 light-years. The Milky Way is estimated to contain 100–400 billion stars." Here is the link: Milky Way
> But if you ask google directly it says 250 Billion + or - 150 Billion.



Duh, <hits head> Of course! I had a bit of a nomenclature failure at one unfortunate spot in my old notes, out by a factor of 1000


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## night_wrtr (Mar 7, 2018)

Venusian Broon said:


> In four billion years the Andromeda galaxy will collide with out galaxy and when these ~1 trillion stars hits our ~300 million...yep, there are expected to be no direct collisions.



Just wanted to step back into this comment because it is mind blowing all on its own when thinking on the vastness of space. Speaking on the power of gravity, even though two galaxies can merge without direct collisions, it will totally destroy their shape and structure. New stars form at a higher rate burning out its resources and will set other stars into a different motion, throwing many out of the galaxy altogether.


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## Venusian Broon (Mar 7, 2018)

night_wrtr said:


> Just wanted to step back into this comment because it is mind blowing all on its own when thinking on the vastness of space. Speaking on the power of gravity, even though two galaxies can merge without direct collisions, it will totally destroy their shape and structure. New stars form at a higher rate burning out its resources and will set other stars into a different motion, throwing many out of the galaxy altogether.



It would be spectacular - loads of gas and dust clouds coming together and being contorted and compressed, would start a wave of new star formation all over the place.

But then some parts would likely be shed, as you say. I was reading that some one had calculated there was a 12% probability* that the sun would be swept out of the resultant mega-galaxy completely. Not in a destructive way, just sort of slowly 'bumped' out. But there was also quite a strong chance we might be dragged into the centre...

Which would be bad, because it's the centre where the real 'light-show' would take place. Eventually, no matter what, the two giant black holes at the centres of each galaxy will eventually merge (possibly the only guaranteed 'collision'!) that will release a catastrophic amount of energy, possibly making the new galaxy a Quasar.

Of course this is 4 billion years in the future - by this stage isn't Sol expected to be a red giant and to have fried Earth to a crisp?

Should give us plenty of time to come up with a plan B.




-------------------------------------------------------

* The mind boggles at how one could come up with a firm figure for that scenario!


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## night_wrtr (Mar 7, 2018)

Venusian Broon said:


> Of course this is 4 billion years in the future - by this stage isn't Sol expected to be a red giant and to have fried Earth to a crisp?



The sun will already be too hot and will have evaporated all the oceans long before it gets there. So we probably only have a billion years left in the habitable zone to figure this out. Maybe we will have a nice set of condos on the shores of Pluto by then.

We might want to start working on this now. Someone put on a pot of coffee, please.


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## Brian G Turner (Apr 18, 2018)

Venusian Broon said:


> This is a bit counterintuitive for me, I'd think there should be more brown dwarfs lying about, but apparently in our vicinity it's just not the case!



Interestingly enough, it may simply be that we haven't yet spotted them - the Bad Astronomy blog suggests that we may yet find one or more even closer than Proxima Centauri: Are we overlooking a lot of nearby brown dwarfs?


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## Venusian Broon (Apr 18, 2018)

Brian G Turner said:


> Interestingly enough, it may simply be that we haven't yet spotted them - the Bad Astronomy blog suggests that we may yet find one or more even closer than Proxima Centauri: Are we overlooking a lot of nearby brown dwarfs?



Slimline brown dwarfs then


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