stars orbiting non-stars

[Didymus]

I tend to rant in other sections because I've done a satisfactory amount of research in other sections.... But I want to start here by freely admitting that I know very little about astronomy. Not going to pretend at all.

 

But a discussion elsewhere lead me to a question I'd like to ask here:

 

Are you aware of examples of a single system in which a star orbits a non-star (not counting black holes)?

 

And, I'm looking for a clear orbit.... I know that technically while the earth orbits the sync the earth does pull the sun a bit, so technically they're orbiting about eachother.... Just in a -very- weighted fashion. But to my knowledge, stars tend to be the most massive object in a system. Stars may orbit each other, non-stars may orbit each other.... But, outside of black holes (retard stars), do we know of a system including a star with a non-star ad the most massive object?

 

 

Mod repellant: the word "retard" is intended in the context that the light from a black hole is held back.... Retarded from advancing through a black hole's gravitational field. This is in no way an accusation of black holes being mentally or emotionally dense because they aren't sentient in the first place.

[swansont]

I don't see how you will get a more massive object that isn't classified as a star.

[CaptainPanic]

How about stars orbiting a gas nebula, on a very long orbit (a nebula which may ultimately form a more massive star, but has not yet)?

I'm no expert in this field either, btw.

 

Btw, Didymus, I don't think that black holes would have reported your post... but it never hurts to be friendly.

[Greg H.]

I don't see how you will get a more massive object that isn't classified as a star.

 

This is the problem I would see with the idea. From everything I know about Astonomy and astrophysics, the lighter object always orbits the heavier one. As Swansont says, I don't see how you would get a more massive object than a star without it also being a star.

How about stars orbiting a gas nebula, on a very long orbit (a nebula which may ultimately form a more massive star, but has not yet)?

I'm no expert in this field either, btw.

 

Btw, Didymus, I don't think that black holes would have reported your post... but it never hurts to be friendly.

 

I don't think that would work, simply because the density of the "more massive" object isn't high enough. Remember, you can calculate gravity by way of density using the proper equation, and if the density of the object drops, so does the gravitational pull it can exert. Nebulae, despite their impressive size, are not very dense at all. I'm not sure you'd get noticeable pull from it.

[Didymus]

well... yea. So, I guess it comes down to "are there any examples of a non-star object more massive than a star being in the same system as a star." ... which one orbits the other is just a question of which is more massive because they both orbit each other... The more massive one is, the less it tends to be pulled around and the more it tends to pull around the other one....

So yea, the sun does orbit the earth. ... a little.

[Greg H.]

If you want to be technical, all orbits are around a common center of mass. It's just that when one object grossly out masses the other, the center of mass tends to be inside the larger object.

 

As for your question, I don't know of any non-star objects more massive than a star except for black holes, regardless of their location.

[Airbrush]

"Are you aware of examples of a single system in which a star orbits a non-star (not counting black holes)?"

 

No

[swansont]

How about stars orbiting a gas nebula, on a very long orbit (a nebula which may ultimately form a more massive star, but has not yet)?

I'm no expert in this field either, btw.

 

Possible, I suppose, but planetary nebulae have densities of around 100-10,000 particles per cm³. By way of comparison, an ideal gas at STP has more than 10¹⁹. You need more than 10³⁰ kg, which is 10³⁰ moles of hydrogen, or around 10⁵⁴ atoms which is 10⁵¹ cm³ or 10⁴⁵ m³. So the characteristic size is of order 10¹⁵ meters, which is a tenth of a light-year for something around the mass of our sun. And the orbiting star has to be outside of that distance.

 

Star-formation nebulae are denser, at about 10⁶ particles per cm³ so that reduces the size by a factor of 10.

[imatfaal]

I think if you want to be slightly tricksy - and from your OP i think you realised that it would come to that - many stars are in galaxies which are in orbit around larger galaxies. We have a couple of dozen dwarf galaxies around the milky way - and what, in mass terms area they actually orbiting? Dark matter! Our galaxy and Andromeda are both about 400:1 Dark Matter: Baryonic Matter - so in any fair description the dwarf galaxies are orbiting non-stellar matter.

 

I was hoping I could say that Sol was in fact orbiting Andromeda along with the rest of the Milky way - but is seems we are not so much orbiting as crashing.

[EdEarl]

The smallest stars can be 8.3% of the mass of the Sun. The smallest neutron star is about 1.4 Solar masses, which means is the largest possible planet (i.e., cold rocky sphere) must be less than 1.4 Solar masses. Any planet larger than 8.3% Solar mass would tend to fuse elements lighter than iron, especially hydrogen and helium--the most abundant elements in the Universe. Therefore, this planet would necessarily be made of iron and heavier elements. Iron is 0.6 as abundant as silicon and hydrogen is 40,000 times as abundant as silicon. Is it possible a star orbits a planet, yes. Is it likely, IMO no, even though the universe is very large. It is possible a star orbits a burned out star, but it would be very hot compared to a planet.

 

I'm not an expert, and may have made a mistake in this analysis.

[CaptainPanic]

 

Possible, I suppose, but planetary nebulae have densities of around 100-10,000 particles per cm³. By way of comparison, an ideal gas at STP has more than 10¹⁹. You need more than 10³⁰ kg, which is 10³⁰ moles of hydrogen, or around 10⁵⁴ atoms which is 10⁵¹ cm³ or 10⁴⁵ m³. So the characteristic size is of order 10¹⁵ meters, which is a tenth of a light-year for something around the mass of our sun. And the orbiting star has to be outside of that distance.

 

Star-formation nebulae are denser, at about 10⁶ particles per cm³ so that reduces the size by a factor of 10.

 

Right, so let us increase the mass and volume of that nebula by a factor 1000, then the characteristic size would logically increase by a factor 10, and the size becomes one light year. You can totally have a star at 4 light years (distance of our Sun to the Centauri system) orbiting such a heavy nebula. I admit that it would be a long orbit, which takes many thousands of years... but I am not sure if our OP cares about that.

[swansont]

 

Right, so let us increase the mass and volume of that nebula by a factor 1000, then the characteristic size would logically increase by a factor 10, and the size becomes one light year. You can totally have a star at 4 light years (distance of our Sun to the Centauri system) orbiting such a heavy nebula. I admit that it would be a long orbit, which takes many thousands of years... but I am not sure if our OP cares about that.

 

There can also be no other star within that distance, or else you would be orbiting the star. (BTW I get an orbital period of tens of millions of years, but I didn't double-check the numbers)

[theholykrael]

I apologise for being a little late to this discussion, but as an avid student of Astronomy and Physics, I thought I'd make a suggestion for a possible setup.

 

Firstly though, I've seen it mentioned that "The lighter object orbits the heavier one", and while I appreciate the logic that's actually not strictly the case. You can take as an example any number of stars in binary orbits, where you may have a range of differing masses, and even mass exchange between them (hence the term Mass Exchange Binaries).

 

My own personal thoughts are that you could have a very young star orbiting at a reasonable distance from a protostellar accretionary disk.

Basically that's a star orbiting what will eventually also be a star, and likely a few planets.

[Didymus]

Aye, I'm definitely a believer that gravity is 2-ways. The earth pulls me down with a force of 150 pounds.... I pull the earth with a force of 150 pounds. Only reason I move more than it is because its inertia is bigger than mine. Likewise the earth orbits the sun.... But the sun does orbit the earth.... A bit.

 

Thank you for your input.

[Z07]

If the barycenter is within one object then the two objects don't orbit each other. The example of the Earth and the Sun has the barycenter well within the Sun. In the Earth-Moon system the barycenter is within the Earth. In those examples, therefore, the Earth orbits the Sun and the Moon orbits the Earth. The Sun doesn't orbit the Earth "a little".

[Greg H.]

If the barycenter is within one object then the two objects don't orbit each other. The example of the Earth and the Sun has the barycenter well within the Sun. In the Earth-Moon system the barycenter is within the Earth. In those examples, therefore, the Earth orbits the Sun and the Moon orbits the Earth. The Sun doesn't orbit the Earth "a little".

Technically neither one orbits the other; they both orbit the barycenter of the system. This is why stars wobble when they have a solar system (or a companion star) attached to them. It is, in fact, possible for the barycenter of the solar system as a whole to exist above the surface of the sun, given the proper planetary alignments:

 

 

 

If all the planets were aligned on the same side of the Sun, the combined center of mass would lie about 500,000 km above the Sun's surface.¹

 

So if you really wanted to be technical about it, it's also wrong to say the Earth orbits the Sun.

---

1. Barycentric Coordinates (Astronomy) - Wikipedia

[acsinuk]

Just joined this forum.

The idea of non-stars is most interesting as these would normally be called major planets and I suppose if there was only one major planet and a smallist star then the pair would orbit the common gyro barycentric centre as shown in the wiki reference above.

The question is why do stars give out energy and planets, asteroids moons etc all absorb energy.

Could it be that stars are made of antimatter whilst everything outside of the stars surface is made of matter?? What do you think?

CliveS

[ajb]

The question is why do stars give out energy and planets, asteroids moons etc all absorb energy.

Could it be that stars are made of antimatter whilst everything outside of the stars surface is made of matter?? What do you think?

CliveS

Everyting absorbs and reemits energy.

 

And we know why stars emitt so much energy, they convert there mass into energy via nuclear fusion.

[swansont]

Just joined this forum.

The idea of non-stars is most interesting as these would normally be called major planets and I suppose if there was only one major planet and a smallist star then the pair would orbit the common gyro barycentric centre as shown in the wiki reference above.

This is an issue I alluded to earlier — it's quite likely you can't have a planet that is more massive than a star, because then the planet would simply collapse under its own gravity and start the fusion process, i.e. it's a star.

[Didymus]

Bingo. That's the point of this thread.

 

 

I.e. if mass is required for fusion then.... Yes fusion is the process for giving off light and heat and radiation.... But the source of the energy for fusion is gravity.

 

Thus solar power, wind power, hydroelectric power are all second hand means to harness the force of gravity. Thus energy being created since gravity being harnessed and work performed does not deplete a finite amount of gravity that exists within an object. Thus negating the conservation of energy.

[ajb]

...deplete a finite amount of gravity that exists within an object. Thus negating the conservation of energy.

What is an "amount of gravity"?

 

The main source of energy for a star is its mass. Nuclear fusion converts some of this mass into energy.

[acsinuk]

Wait a minute though. Originally, we had to conserve mass but after relativity we decided that what we really meant was that we must conserve energy. Right . But because there is nothing identifiable inside molecules apart from the electric charges and neutrons so why dont we establish the new physics law that only electric charge must be conserved and further that if these charges are not balanced that the resultant unbalance will be emitted as electromagnetic energy. Simple!

CliveS

[ajb]

....further that if these charges are not balanced that the resultant unbalance will be emitted as electromagnetic energy.

I don't quite see what you are saying. However we do know that accelerating electric charges emitt electromagnetic radiation.

[swansont]

Bingo. That's the point of this thread.

 

 

I.e. if mass is required for fusion then.... Yes fusion is the process for giving off light and heat and radiation.... But the source of the energy for fusion is gravity.

 

Thus solar power, wind power, hydroelectric power are all second hand means to harness the force of gravity. Thus energy being created since gravity being harnessed and work performed does not deplete a finite amount of gravity that exists within an object. Thus negating the conservation of energy.

 

Fusion is exothermic. It does not need a source of energy, as such. What is required are the conditions to overcome an activation potential.

[EdEarl]

 

ScienceDaily.com Sep. 5, 2013 — Astronomers are constantly on the hunt for ever-colder star-like bodies, and two years ago a new class of objects was discovered by researchers using NASA's WISE space telescope. However, until now no one has known exactly how cool their surfaces really are -- some evidence suggested they could be room temperature.

 

A new study shows that while these brown dwarfs, sometimes called failed stars, are indeed the coldest known free-floating celestial bodies, they are warmer than previously thought with temperatures about 250-350 degrees Fahrenheit.

The article also says that if one of these objects was orbiting a star, it would probably be called a planet. Thus, a star just slightly larger than one of these cool brown dwarfs orbiting with a cool brown dwarf, will probably be called a star and planet. Since the two can be fairly close in size, they may orbit each other with the center of rotation being outside both of them. IMO it is not a non-star orbiting a star, but that's just my opinion.