# Questions tagged [binary-stars]

Binary stars are a system of two stars rotating around their center of mass, as opposed to single stellar systems such as our solar system.

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### Can Binary Stars Escape Each Other?

updated 8/27/2020 While the recession of our Moon from the Earth may slow and even stop, (see When will the Moon reach escape velocity?) binary star systems will (1) never stop experiencing mutual ...
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### Definition of eclipsing binaries?

In the second minimum (the 3rd step) there is a smaller decrease in light intensity. For this to happen, wouldn't you need to be looking at the plane of orbit from above rather than directly along the ...
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### Gravitational force between astronomical bodies in a binary system

If two celestial bodies of similar mass form a binary system and both have fairly relativistic velocities does in that case gravity act with delay and does the picture shown present the problem in the ...
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### Keplerian orbital elements of a binary system: computing the eccentricity vector and angular momentum vector

I have been given a binary system and know a few of the keplerian orbital elements such as ...
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### Ratio of masses of double star problem

I am currently studying Classical Mechanics, fifth edition, by Kibble and Berkshire. Problem 2 of chapter 1 is as follows: The two components of a double star are observed to move in circles of radii ...
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I don't think context is needed but to make sure: I'm doing a homework exercise on binary system. P is the orbital period and E the energy of the system. The following is in the solution when trying ...
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### How do tidal forces change gravitational waves

If there is a binary of two neutron stars, they are going to be deformed because of the tidal forces. I suppose that it will cause a change in the movement of the stars and that will cause a change in ...
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### Eccentricity of two bodies in an unbound orbit

There seems to be two definitions of an eccentricity of orbiting bodies, one for when it’s not bound and the other for when it is bound (Keplerian binary). When the binary is bound there is a simple ...
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### Derive hamiltonian from equations of motion

Is there a method for deriving the hamiltonian given that you know the equations of motion? For example given the equation (equation 5 in paper linked) they simply the derive the Hamiltonian in ...
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### Discerning binary stars

What is the minimum magnification that one would need to discern a pair of binary stars if viewed from Earth? Are there factors other than magnification that matter? If so, why?
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### In which direction would gravitational waves be emitted when two black holes colide?

Imagine two black holes on the x-axis coming together at the origin (not rotating around each other, just falling towards each other). In which direction would the most intense gravitational waves be ...
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### Why do gravitational waves circularize a binary?

I understand that a binary orbiting around one another will circularize due to the emission of GWs due to Peters equations and that highly eccentric binaries evolve faster. But GW emission also ...
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### Find first lagrange point from potential energy of binary system [duplicate]

I am trying to solve a question of a course that I need to TA tomorrow and I am not sure what I am missing here. You first have to derive the potential energy of a test source in a binary system, ...
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### Are there any black hole neutron star binary?

Has a black hole-neutron star binary aver been observed? I mean observed in any way: gravitationally, through eclipse, or any other means. EDIT Thanks to the comment to this question, we know that ...
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### How does the mass loss in a binary system affect the semi-major axis of the orbit?

It is common that during the stellar evolution one of the stars in a binary system would transfer mass into the the other, resulting in the increase of mass of one star and decrease of mass of the ...
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### Why does mass (gas) transfer between binary stars cause them to move apart?

Some binaries, like Algol binaries, move monotonically apart from each other as one steals gas from the other. Why? On a naive level, shouldn't friction and such cause the two stars to move (rotate?,...
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### Existence and evolution of P-type “asymmetrical binaries”

I'm not sure how those are called so let me explain what I mean by "P-type asymmetrical binaries" - I'm thinking of two stars of very different masses (originally) that orbit each-other fairly closely....
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### Free fall and gravitational waves

If you take the Earth-Moon system, from what I understand, the Moon for instance is in free fall towards the Earth-Moon center of mass. However Einstein's equivalence principle says that a body in ...
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### Roche lobes in binary star systems

While studying mass transfer in binary star systems, I came across the concept of Roche lobes and the role of the inner Lagrangian point $L_1$, as shown in the adjoining figure. However, I am having ...
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### What happens to the accretion disk when two black holes merge?

I'm aware that accretion disks around black holes are formed from the swirling mass of matter that is slowly being stripped of its atoms, but what happens to it when two black holes merge? I was ...
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### Position vector of an eccentric binary

For a circular, equatorial ($z=0$) Newtonian binary, the position can be clearly written as, $$x_i = r(\cos \Omega t, \sin \Omega t, 0)$$ for orbital frequency $\Omega$. My question is how would ...
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### Moving objects and gravitational radiation

I have read that GR predicts that moving, massive objects emit some of their energy as gravitational waves. In reality, the energy loss is negligible and undetectable, but in some systems, like PSR ...
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### How do neutron star binaries form?

Do neutron star binary systems come from previously active-star binaries, where where both stars have gone supernova and left behind neutron stars that are still in orbit? Or do they form when two ...
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### What's the shortest “safe” distance from a neutron star merger?

Take GW170817 for example, the first neutron star collision picked up by LIGO. Given how much data we got from that event, can anyone figure out what the "blast radius" is, and how far away from the ...
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### Event-Horizon Shape in a Binary System

I understand that a solitary black hole has a spherical event horizon. I was wondering whether this still stands in a binary system of two (let's say equal mass) black holes? Could the proximity of ...
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### Why is relativistic beaming/ Doppler beaming occur at non-relativistic speeds

The reflexive motion of a binary star system causes the host star to occasionally wobble towards and away from an observer on Earth, which gives rise to an effect called relativistic beaming. This is ...
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### Which orbit planet will take with 2 stars?

Is there a law or an equation that shows which star gravity will win and suck a a planet that has 2 stars Assume planet P has 2 stars A & B A is smaller than B Planet P is closer to A more than ...
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### Theoretical solution to binary black hole merger based on Hawking and Ellis

Following Hawking and Ellis, Chapter 9, Fig. 60, Pg. 322, the following figure is meant to illustrate the contrast between apparent horizons and event horizons in the case of a binary black hole ...
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### How do inspiraling black holes get closer?

In Newtonian mechanics, binaries are stable. We here on earth are very glad that it will not emit its angular momentum and spiral into the sun. What is different about the black holes and neutron ...
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### Orbital velocity of a binary system

My goal is to find a velocity vector for two planets so that they orbit each other. The planets' masses and distances are known, just not their velocities. When googling for an equation, I found a ...
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### Wind-fed Accretion and White Dwarf stars

Can a White Dwarf star in a binary system accrete matter via the Wind-fed accretion process?
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### Gravitational waves and chirp waveform

When two neutron stars collide emitting gravitational waves, what exactly does the chirp waveform represent and how is it used to infer the distance to the source?
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### On what timescale does gravitational wave emission circularise an orbit?

Gravitational waves remove both energy and angular momentum from a binary orbit. Both rates are enhanced in non-circular (eccentric) orbits and I presume that (like tidal friction) the net effect will ...
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### On Planets orbiting binary stars

Several years ago a discovery was made of planet orbiting a star of a binary system (two stars orbiting each other). Since binary star systems are plentiful in our galaxy, I presume we will be ...
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### Time dilation, and curvature of space caused by two black holes of unequal masses

If you were to try to find the time dilation in a region of space near a black hole you would use the equation $$t_r=\sqrt{1-\frac{2GM}{rc^2}}$$ Would the time dilation from two black holes be this? ...
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### Magnetar's magnetic field near a black hole (novice question)

Even light cannot escape the event horizon of a black hole. Now, imagine a magnetar orbits a black hole. The magnetar orbits too far to be ripped and consumed by the black-hole. However, its magnetic ...
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### How do compute an energy momentum tensor, given some equations of motion

This problem can be found in a paper called "Gravitational Radiation From Point Masses In A Keplerian Orbit", but I do not have access to this, so cannot see how to do it. I have been given ...
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### Penrose diagram for two black holes?

Is there a Penrose diagram for two black holes near each other. Perhaps they are colliding or circling each other? Or can this method only describe a single black hole.
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### Barycenter of a binary star system

It is said that the barycenter of 11 Draconis (Thuban) and 10 Draconis which compose a binary star system is a central point. Is this central point a material or immaterial object? Does the size of ...
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### When a star undergo collapse in a binary system what effect it has on its companion star? [closed]

when a star in its lifetime fuses up all its hydrogen and then collapse under gravitational force, till the temperature inside become high enough to restart the fusion of helium and radiation pressure ...
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### Are all binary stars also variable stars?

Since variable stars are the once whose luminosity change according to our perception and all binary stars must go through eclipsing, Can we say that all binary stars are also variable stars?
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### Binary Stars In the Universe

Almost 80% of stars seen in the universe are Binary stars.What makes them so abundant in the universe? Why isn't there other numbers but exactly two that is abundant?
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### Would two objects orbiting each other emit gravitational waves on every direction or only on their plane of rotation?

Imagine a system where two massive objects are orbiting each other, something like a binary black hole or neutron star system. Such a system should emit gravitational waves. I'm curious on the ...
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### The contact binary star system in Cygnus

Astronomers are predicting that they will combine in 2020. Thus creating a red nova that will be visible to the naked eye here on earth. The stars are about 1,800 light years from earth. My question ...
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### How does the delay of pulsar signals prove that gravity travels at the speed of light?

In the Hulse-Taylor binary pulsar system, the orbit of the two neutron stars results in the warping of space time causing the pulses to arrive earlier and later because of the longer distance ...
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### What happens to the singularities of two black holes in the moment they merger?

Let's assume the merger of a binary black hole and consider especially the moment of the transition from the last stable orbit to the merger, i.e. the transition where two black holes form one black ...
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### Hulse-Taylor binary data gap in the nineties

I was wondering what is the reason there are no data points in the famous Hulse-Taylor plot of the period decay in the 1990s. Does anyone know why no one collected data during this period?
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### Rotating Binary Blackhole Double (Kerr) Solution Approximation

As a continuation of my previous inquiry, since the Kerr spacetime metric ds^2=-c^2d\tau^2=-\left(1-\frac{r_sr}{\Sigma}\right)c^2dt^2+\frac{\Sigma}{\Delta}dr^2+\Sigma d\theta^2+\left(r^2+a^2+\frac{...