could andromeda and milky be in eliptical orbit?

[R1]

Is it possible that Andromeda and The milky way are in some oblong binary orbit.<br /><br />the most recent redshift for Andromeda is around -300, but wouldn't that strictly mean that the<br />spacetime between us is contracting and still be possible that we're in some kind of fast oblong<br />binary orbit since redshift doesn't tell us anything precise about 3D movement except for recession vs. approaching?<br /><br />I thought about parallax but wouldn't we need to look at it from 2 somewhat separated parts in the Milky way to get accurate (if we use parallax)?<br /> <div class="Discussion_UserSignature"> </div>

 

[Boris_Badenov]

<font color="yellow"> <br />Is it possible that Andromeda and The milky way are in some oblong binary orbit. <br /><br /> </font><br /><br /> Excellant question. How would you find out? <div class="Discussion_UserSignature"> <font color="#993300"><span class="body"><font size="2" color="#3366ff"><div align="center">. </div><div align="center">Never roll in the mud with a pig. You'll both get dirty & the pig likes it.</div></font></span></font> </div>

 

[alkalin]

Good point about parallax. We are traveling fairly rapidly around the MW’s center, so in a few years perhaps we might have enough distance between two points to utilize parallax. One problem would be figuring out where we are precisely in our orbit about the MW because this orbit is not precise. It is being influenced by the nearby stars. On local stars I think it is good to only about ten thousand lys utilizing the earth’s orbit around the sun. <br /><br />Parallax would give us a more precise measurement of the distance to Andromeda, but still may not determine orbits of the two galaxies. But there is a good possibility as you suggest that the two are in some kind of orbit about one another. It is not very common for galaxies to actually collide. <br />

 

[MeteorWayne]

Actually, we may be destined to collide.<br /><br />Here's a simulation of the collision <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[R1]

how distant do we need to make the next observation from the earliest measurement we took<br />in order to use parallax measurement? <br /><br /><br />I think motion in a direction other than straight towards us should be detected soon.<br />but we really need to measure as many Andromeda stars as possible and measure their change with respect to <br />more distant objects in its background.<br /><br /><br />I just don't know if by the records not mentioning any other motion other than straight towards us it means<br />that <br /><br />a) they had had sufficient time and measurement completed and they're sure it's 'only' moving towards<br />us, or <br />b) does it mean they're working on this, or <br />c) maybe that they're not even working on this?<br /><br />I wish all the articles I find would elaborate some more.<br /> <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

I would say people are working on it.<br />However while the speed toward us of 300 km/sec is well known due to doppler measurement, the distance to Andromeda is poorly constained (probably +/- 10% or more), and it will take some time to get accurate sideways position measurements. Then converting those measurements to velocity will be subjuct to the distance error.<br />Better estimates might come in our lifetime, but it will likely be thousands of years before anything can be stated with certainty, IMHO. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[doubletruncation]

Recently the proper motions for the LMC and SMC have been measured to better than 10% with hubble from only a 2 year baseline. (See http://xxx.lanl.gov/abs/astro-ph/0508457 and http://xxx.lanl.gov/abs/astro-ph/0606240 ). The proper motion of the LMC is about 2 milli-arcsec per year, whereas that expected for Andromeda (though not measured yet) is about 50 times less than that. Either improving the telescope resolution by a factor of ~50 or waiting 50 years we should be able to get the proper motion for Andromeda as well. One possibility is to look for masers in andromeda since you can then observe them with incredibly high resolution using a Very-Long Baseline Interferometry radio telescope network. This has actually been done for M33 (the other big galaxy in the local group, which is often overlooked for its bigger neighbor andromeda, though honestly I think M33 is far more beautiful!) - see for example http://xxx.lanl.gov/abs/astro-ph/0503058 . <br /><br />Also note that parallax is not the only geometric way of getting distances. You can also use eclipsing binaries to get ~geometric distances (you measure the radius, and mass of the stars geometrically, you measure the temperature of the stars spectroscopically so you know their physical luminosity. You then get the distance from the inverse square law. The biggest assumption making that goes on in this game is the ratio between total and selective extinction by dust). This has been done for an eclipsing binary in Andromeda (see http://www.astronomy.com/asy/default.aspx?c=a&id=3640 ), and the quoted uncertainty in the distance is about 5% and is consistent with, but substantially more precise than, the other distance in <div class="Discussion_UserSignature"> </div>

 

[vandivx]

"<br />Is it possible that Andromeda and The milky way are in some oblong binary orbit."<br />----------<br />I should think that is certain given that our galaxy along with Andromeda and many others are part of local cluster of galaxies which is graviationally bound conglomeration extending all the way to supercluster structures which are all gravitationally bound structures, albeit somewhat loosely<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>