<p>There is no indication nor any astrophysical reason for such a scenario. The most relevant constraints are</p>

<ol>
<li>The Solar velocity is typical for stars in our immediate Galactic neighbourhood. </li>
<li>Soft binaries (those with orbital velocity smaller than the local velocity dispersion $\sigma$) dissolve (Heggie's law: soft binaries become softer and hard binaries harder).</li>
</ol>

<p>These are in contradiction with a Solar binary nature: a viable binary has a large orbital velocity that would put the Sun outside of the typical velocity for local stars. This contradiction can only be temporarily avoided if the current (but not in $\sim1000$ years) orbital velocity and the velocity of the massive binary companion add up to a typical stellar velocity. This is an unlikely chance.</p>

<p>Binaries with a stellar-mass black hole always form from an ordinary stellar binary, with one of the stars going supernova. Often, such binaries are quite compact. All this is ruled out for the Sun.</p>

<p>Finally, black holes of intermediate masses (100 to $10^5$ M$_\odot$) haven't (yet?) been detected unambigously (though there are several objects that have been claimed to be such intermediate-mass black holes also IMBHs).</p>

CC BY-SA 3.0
2015-04-28T15:10:27.740Z
You are very professional, haha. What I asking is an unusual case.  Let me put it this way. Can we tell there is a massive black hole nearby just based on the orbit of our sun? In sun's 3D velocity, there may be a small component caused by the black hole.
questionhang
CC BY-SA 3.0
2015-04-28T15:47:31.203Z
Walter, the Sun does have a peculiar velocity with respect to the local standard of rest of some 10 km/s. I'm not sure what you mean by a "viable binary", but if the Sun were in orbit with a 1000 solar mass black hole in say a $10^4$ year orbit I don't think the orbital motion could be discerned (it would be less than a few km/s). I think the argument would more likely be based on subtle tidal effects on the orbits of the solar system planets that would have become evident. And there are other arguments...
ProfRob
CC BY-SA 3.0
2015-04-28T16:00:37.013Z
@rob  there are visible tidal effects on our solar system now? Anything weird happens in our solar system?
questionhang
CC BY-SA 3.0
2015-04-29T07:43:04.510Z
"Anything weird happens in our solar system?" What kind of question is this? This is guy is not serious at all...
Joan.bdm
CC BY-SA 3.0
2015-04-29T10:34:40.720Z
@joan I am looking for useful comments or suggestions.  It is a dumb question?  I learned a lot from Walter's comment. How about yours?
questionhang
CC BY-SA 3.0
2015-04-28T14:30:03.740Z
2015-04-28T14:30:03.740Z
Walter
<p>Can we track its orbit well now?<br></p>

<p>There is any study that may indicate our sun may be a companion of a big black hole?<br/> </p>

<p>What is the current constrain about its orbit now? There is a 1000 solar mass black hole within 10 pc?</p>

CC BY-SA 3.0
2015-04-28T13:13:37.787Z
Are you referring to Sagittarius A?
user6760
CC BY-SA 3.0
2015-04-28T13:40:23.080Z
@user6760  Sar A* is 8 kpc away, man.
questionhang
CC BY-SA 3.0
2015-04-28T14:53:59.827Z
"Can we track its orbit": does "its" stand for the Sun or for the BH? By "companion" you mean that the Sun is in a binary system? If so there are tens of threads about this already.
Py-ser
CC BY-SA 3.0
2015-04-28T15:35:32.350Z
Are you in fact asking *if* there were a 1000 solar mass black hole nearby, whether we would know based on the kinematics of stars in the solar neighbourhood?
ProfRob
CC BY-SA 3.0
2015-04-28T15:39:35.147Z
@rob  yes, not necessarily 1000M⊙. How much is the max(mass)  that we can exclude currently?
questionhang
<the-sun>
Could our Sun be a companion star of a massive black hole?
questionhang
# Could our Sun be a companion star of a massive black hole?

(Asked by: username_0 on 2015-04-28)

Can we track its orbit well now?

There is any study that may indicate our sun may be a companion of a big black hole?

What is the current constrain about its orbit now? There is a 1000 solar mass black hole within 10 pc?

**Tags:** the-sun
> **Comments:**
> **username_1**: Are you referring to Sagittarius A?  
> **username_0**: @user6760  Sar A* is 8 kpc away, man.  
> **username_2**: "Can we track its orbit": does "its" stand for the Sun or for the BH? By "companion" you mean that the Sun is in a binary system? If so there are tens of threads about this already.  
> **username_3**: Are you in fact asking *if* there were a 1000 solar mass black hole nearby, whether we would know based on the kinematics of stars in the solar neighbourhood?  
> **username_0**: @rob  yes, not necessarily 1000M⊙. How much is the max(mass)  that we can exclude currently?  

---

## 1 answers

### Answer by username_4 on 2015-04-28. Score: 2

There is no indication nor any astrophysical reason for such a scenario. The most relevant constraints are

1. The Solar velocity is typical for stars in our immediate Galactic neighbourhood.
2. Soft binaries (those with orbital velocity smaller than the local velocity dispersion $\sigma$) dissolve (Heggie's law: soft binaries become softer and hard binaries harder).

These are in contradiction with a Solar binary nature: a viable binary has a large orbital velocity that would put the Sun outside of the typical velocity for local stars. This contradiction can only be temporarily avoided if the current (but not in $\sim1000$ years) orbital velocity and the velocity of the massive binary companion add up to a typical stellar velocity. This is an unlikely chance.

Binaries with a stellar-mass black hole always form from an ordinary stellar binary, with one of the stars going supernova. Often, such binaries are quite compact. All this is ruled out for the Sun.

Finally, black holes of intermediate masses (100 to $10^5$ M$\_\odot$) haven't (yet?) been detected unambigously (though there are several objects that have been claimed to be such intermediate-mass black holes also IMBHs).

> **Comments:**
> **username_0**: You are very professional, haha. What I asking is an unusual case.  Let me put it this way. Can we tell there is a massive black hole nearby just based on the orbit of our sun? In sun's 3D velocity, there may be a small component caused by the black hole.  
> **username_3**: Walter, the Sun does have a peculiar velocity with respect to the local standard of rest of some 10 km/s. I'm not sure what you mean by a "viable binary", but if the Sun were in orbit with a 1000 solar mass black hole in say a $10^4$ year orbit I don't think the orbital motion could be discerned (it would be less than a few km/s). I think the argument would more likely be based on subtle tidal effects on the orbits of the solar system planets that would have become evident. And there are other arguments...  
> **username_0**: @rob  there are visible tidal effects on our solar system now? Anything weird happens in our solar system?  
> **username_5**: "Anything weird happens in our solar system?" What kind of question is this? This is guy is not serious at all...  
> **username_0**: @joan I am looking for useful comments or suggestions.  It is a dumb question?  I learned a lot from Walter's comment. How about yours?  

---

