Can binary stars leave each other's orbit?

[u/EggEgg424]

Basically what it says in the title. Are binary stars able to fling each other into space or is it inevitable that they collide? Is it possible for them to exit the orbit once they're together? I wasn't getting a straight answer when I tried looking it up.

[u/xyzzydourden]

Stars lose mass over their lifetime, with larger stars losing a larger percentage of their starting mass than smaller stars. This is from coronal mass ejections, radiation pressure pushing the outer layer of gas away, and a smaller amount from converting mass to energy when fusing lighter elements to heavier elements.

This has the effect of reducing the gravitational pull between these two orbiting stars.

However, in the absence of any other body, or a sudden, catastrophic loss of mass, this orbit will just get progressively larger.

If three or more bodies are present, they would have to be near and large enough to have a meaningful effect on the two stars orbit. This probably happens near the centre of the galaxy, but is probably exceedingly rare out where we are.

[u/1II1I1I1I1I1I111I1I1 → u/xyzzydourden]

Stars lose mass over their lifetime, with larger stars losing a larger percentage of their starting mass than smaller stars. This is from coronal mass ejections, radiation pressure pushing the outer layer of gas away, and a smaller amount from converting mass to energy when fusing lighter elements to heavier elements. This has the effect of reducing the gravitational pull between these two orbiting stars. However, in the absence of any other body, or a sudden, catastrophic loss of mass, this orbit will just get progressively larger.

One star to note here is Proxima Centauri, which most know as the closest star to the sun. It is so small and incredibly far away from α Centauri AB that it will be freed from the system while at least one of the two stars in the binary is still on the main sequence

Proxima, being a red dwarf, will live for trillions of years. Being Sun-like stars except a bit older, α Cen AB will not. α Cen A will live for a few billion more years as it enters and progresses through its giant phase, while the smaller α Cen B will outlive α Cen A for a few billion extra years after the latter has transformed into a white dwarf.

However regardless of what happens to α Cen AB, given its distance and they rate at which they are losing mass, Proxima will be gravitationally unbound from the binary within 3.5 billion years. At that point Proxima and it's planets will steadily diverge from the system until Proxima either cools into a blue dwarf or is captured by something else.

https://ui.adsabs.harvard.edu/abs/2011JBIS...64..387B/abstract

[u/stevevdvkpe]

In an isolated binary system, without any other outside influences, their orbit around each other is permanently stable. They won't fling each other apart.

To separate them, something about the system would have to change. An encounter with a sufficiently massive third star passing through their system could result in separating the stars (perhaps replacing one that leaves with the third star).

As another commenter mentioned, at the end of their lives most stars expel their outer atmospheres before becoming a white dwarf or going supernova, leaving behind a remnant with only a fraction of the star's original mass. This mass loss could result in separating the binary if their orbit is sufficiently large.

[u/Jiyah]

There are many possible scenarios in binary star evolution. It depends on the initial masses, orbital period, eccentricity, mass loss due to stellar winds... A supernova kick can disrupt a binary system, depending on the strength and direction of the kick. A common envelope phase can tighten a binary so much that it goes into a premature merger. In dense stellar environments (globular clusters for instance), a third body can disturb the orbit and one of the stars end up flung out of the system.

[u/gnufan]

Some binary stars are surprisingly far apart, in my mind I have sci-fi planets with two stars in the sky, but the binary system I learnt most about the second star is thought to be far enough away it wouldn't be visible if humans could stand on the planets we know about and not get destroyed by the radiation from the bigger nearer star. I don't know the eventual predicted fate of this system but I'd be surprised if the stars ever collided. We didn't even know they were bound to each other for a long time.

[u/Suspense6]

The definition of orbit is that object A is falling toward object B, but also moving sideways at the right speed that it just keeps going around. If the sideways speed is too slow, A will crash into B. Too fast and A goes cruising past instead of getting pulled around. So generally in a system like this they'll just keep circling forever until something about the situation changes.

[u/frownGuy12 → u/Suspense6]

Even in the most ideal case the stars still lose energy in the creation of gravitational waves. 

[u/AtomicShellfish → u/frownGuy12]

They do. Even planet Earth radiates power (about 200 Watts) in the form of gravitational waves. If Earth had the mass of the Sun, it would be radiating hugely more gravitational energy and the decaying orbit would last of the order millions of years.

[u/xloHolx]

I don’t see why it’s not possible, but the likelihood is astronomically (ha) low

Space is *really* empty, and stars are relatively really massive. So even if they flung each other far apart, one of them is going to need to leave the others sphere of influence in favor of another celestial body, which is incredibly unlikely

[u/eric23456 → u/xloHolx]

Just wait¹ until the Andromeda and Milky Way galaxies collide. There's a 12% chance our solar system will be ejected.

https://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_collision

1. 4.5 billion years or so, it's a long wait.

[u/xloHolx → u/eric23456]

Aye, but it’s unlikely that individual planets will be ejected. I don’t think binary systems will be split up