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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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230 views

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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59 views

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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1answer
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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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63 views

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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0answers
43 views

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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1answer
36 views

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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584 views

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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1answer
158 views

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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91 views

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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102 views

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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1answer
183 views

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 a ...
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1answer
109 views

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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1answer
49 views

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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64 views

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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1answer
39 views

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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1answer
29 views

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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1answer
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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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1answer
321 views

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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1answer
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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{...
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3answers
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Kepler's 3rd law applied to binary systems: How can the two orbits have different semi-major axes?

I suddenly came to the realization that I don't understand something about Kepler's law when applied to binary systems, because I encountered an apparent paradox. There must be an error somewhere in ...
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1answer
122 views

Binary System in General Relativity: Analytical Metric?

My question is quite simple, why an analytical metric can't be found for a static binary system, even for a system under the Schwarschild condition : low field, in the vacuum between the bodies so $T_{...
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165 views

Can planets orbiting a binary star trace out an orbit in the form of an 8 (or $\infty$-sign)? [duplicate]

In this article there is a lot explained about planets orbiting a binary star. It is said that a planet orbits the binary star around the CM of both stars. I couldn't find anything about planetary ...
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2answers
189 views

Spacetime geometry with a system of $n$ interacting black holes [closed]

The Schwarzschild metric is given by $ds^2=-\left(1-\frac{2GM}{rc^2}c^2\right)dt^2+\left(1-\frac{2GM}{rc^2}c^2\right)^{-1}dr^2+r^2d\Omega^2,$ for $d\Omega^2$ the round metric on the $2$-sphere, in ...
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2answers
54 views

Kerr BH effects on inspiral binaries

In the gravitational wave calculation for binary systems: what is the effect of rotation of two BH (or neutron stars, BH-NS,...) on the usual calculations? Is there any EXACT result known?
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2answers
94 views

Is there a model relating GW signal and luminosity of the merger / burst?

To understand fully the importance of the recent observation I would like to know if it is possible to infer the distance or luminosity (in whatever wavelength, or say, the overall power) of the ...
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1answer
68 views

How to identify binary stars in $N$-body simulation?

Binary stars constitute a significant portion of the stars of a globular cluster. I would like to verify that this is true in my $N$-body simulation, but I don't know how to decide whether a star in ...
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1answer
40 views

How would spin of a binary depend on its mass?

I have been reading an article about a code that uses precession analysis on spin of binaries. At the beginning of the article authors describe units of code where they take $c=1$ (speed of light) and ...
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1answer
57 views

Do the stars of the Hulse-Taylor binary follow geodesics?

The Wikipedia definition of a geodesic is, the worldline of a particle free from all external, non-gravitational forces Now for a binary system like Hulse-Taylor I have heard it described as a ...
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78 views

Minimal value of angular momentum in a close binary

I just noticed something interesting with the angular momentum of a close stellar binary. This question is somewhat related to another question of mine, but the question here is clearly different : ...
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1answer
668 views

Conservation of spin angular momentum in a close binary system

Consider a simple model of a close stellar binary, of mass $m_1$ and $m_2 < m_1$, moving on circular orbits around the system's barycenter (no eccentricity, to simplify things). Both star's ...
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2answers
131 views

Paradox from mass transfer in a close stellar binary

I'm considering a simple binary system made of two stars, of mass $m_1$ and $m_2 < m_1$, on circular orbits around their center of mass. Using Newton's theory of gravitation, it is easy to prove ...
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715 views

Quadrupole moment tensor

I am currently working on gravitational waves, and as in every lecture on general relativity I derived the symmetric trace-free perturbation of a Minkowski metric with the Lorenz gauge condition, ...
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1answer
1k views

Mass of each star in a binary star system?

A binary star is composed of two stars that orbit around their centre of mass under the influence of gravity. Consider such a system in which two stars have identical mass. In the centre of mass frame,...
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1answer
208 views

The mass and separation of binary system with only information about one star [closed]

If we can observe that a star and an unmeasurable planet are in circular orbit around a common center of mass. If we know the speed of the star to be $100\,m/s$, the mass of the star to be $2 \cdot 10^...
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1answer
335 views

What is a Roche Lobe?

When dealing with Binary systems and their evolution and mass transfers in the systems, why are equipotential surfaces a point of interest? The one which is called the Roche lobe. Why is the ...
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115 views

Double star system; relative orbit in the case of elliptical orbits

In my physics book they say that the relative distance between two stars (that both have elliptical orbits) in a double-star system equals $4.0 AU$ in the pericenter, and $16.0AU$ in the apocenter. ...
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1answer
255 views

On lifetime of binary stars due to orbital decay by gravitational wave radiation

In the paper: gravitational radiation and the motion of two point masses, in the last But one page and the last page the author derives a formula for the lifetime of a binary whose orbit is decaying ...
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2answers
444 views

Will two planets in a binary star system rotate in the same circle around the mass center every period?

I am modeling a two binary star system, and I am wondering if this is the case. The way I have it right now is that I first figure out the mass center, and then the radius from each of the planet to ...
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0answers
199 views

On gravitational-wave radiation changing orbital parameters [closed]

Two celestial objects of mass $m_{1}$ and $m_{2}$ are orbiting around each other on a very elongated ellipse($\epsilon\approx1$). The system is isolated and there is no other proximate celestial body. ...
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1answer
542 views

What happens to the angular momentum of two merging black holes?

Let's suppose that two black holes of roughly equal mass in a binary system forming from say a large mass stellar binary system are in orbits around their center of mass. Further suppose that we are ...
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2answers
188 views

Can a binary star system create a stationary black hole?

Research over the last 200 years suggests that half or more of visible stars are part of multiple star systems. I apologise for the number of assumptions in my question but, because of the numbers of ...
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2answers
929 views

Determining Mass of Spectroscopic Binaries

I know that the mass of a binary star system is given by Kepler's Law: $$\mathrm{m_1 + m_2 = \frac{4 \pi^2 r^3}{GT^2}}$$ Further we know that: $$\frac{r_2}{r_1} = \frac{v_2}{v_1} = \frac{m_1}{m_2}$$ ...