Has Andromeda Moved Closer in 2.5 Million Years?

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Discussion Overview

The discussion revolves around the current position of the Andromeda Galaxy in relation to Earth, specifically whether it has moved closer over the past 2.5 million years, the implications of its movement, and the calculations involved in determining its distance and approach speed. The scope includes theoretical considerations, calculations, and some observational data.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants assert that when observing Andromeda, one sees it as it was 2.5 million years ago, not its current position.
  • There are claims that Andromeda is moving toward the Milky Way at approximately 300 km/s, with some suggesting it is approaching at about 2 billion miles per year.
  • Questions arise regarding whether this movement rate accounts for the effects of dark energy and spacetime acceleration between the two galaxies, with some arguing that dark energy has negligible effects at such scales.
  • Participants present calculations estimating how much closer Andromeda has moved in the last 2.5 million years, with varying results and methods, including one participant suggesting it has moved approximately 2.3562 x 10^19 km closer.
  • There are discussions about the radial velocity of Andromeda relative to the Sun and the implications of the Sun's orbit around the Milky Way on this approach speed.
  • Some participants express uncertainty about the accuracy of their calculations and the assumptions involved, particularly regarding the influence of dark energy and the gravitational binding of the galaxies.
  • Links to external resources and simulations are shared to illustrate the potential future collision between Andromeda and the Milky Way.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the exact calculations of Andromeda's movement or the implications of dark energy. Multiple competing views and uncertainties remain regarding the effects of gravitational binding and the accuracy of distance measurements.

Contextual Notes

Participants express uncertainty about the assumptions underlying their calculations, including the influence of dark energy and the time frame of observations. The discussion includes references to various approximations and the complexities of cosmological measurements.

Who May Find This Useful

This discussion may be of interest to those studying cosmology, astrophysics, or anyone curious about the dynamics of galaxies and their interactions over time.

jonorion
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where is andromeda?

I know that when i look at the andromeda galaxy i am seeing it as it was 2.5 million yrs ago. what i want to know is am i seeing it where it is physically in space now or has it moved closer to us in the 2.5 million yrs that the light has taken to reach us...
 
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Hi and welcome to the forum your seeing where it was not its current position.
 


do you know how much closer to us it is actually?
 


I myself don't nor know how to calculate its current position but I'm sure someone does lol
 


According to the wiki on it, it is moving toward us at 300 km/sec.
 


Does that movement rate account for current spacetime acceleration of the region between andomeda and the milky way?
 


Mordred said:
Does that movement rate account for current spacetime acceleration of the region between andomeda and the milky way?

I think it does. Andormeda and the Milky Way are gravitationally bound, dark energy effects doesn't play a big role at such scales.
 


Astrofan said:
I think it does. Andormeda and the Milky Way are gravitationally bound, dark energy effects doesn't play a big role at such scales.

Mordred said:
Does that movement rate account for current spacetime acceleration of the region between andomeda and the milky way?

Correct. The expansion of the universe has zero* effect since our galaxies are gravitationally bound to each other.

*I say zero, but in reality it is...complicated. The model that predicts and explains expansion models the universe as homogenous when it is not. Whether the metric expansion of space actually happens for bound objects is still up in the air I believe. But either way for all practical purposes we can say it has zero effect.
 
jonorion said:
do you know how much closer to us it is actually?
(according to sites)
Adromeda galaxy is approaching (moving) at about 2 billion miles per yr, 100 to 140 km per second, distance of 2.5 million light years and 'predicted' to be in collision after an initial approx 4.5 billion yrs but the photon we're observing happened (approx) 2.5 million light yrs ago(limitation of light speed). Were getting an actual approximation of 2.5 billion yrs. Here is an (approx) diagram of distance getting closer.

http://www.dmuller.net/cosmology/andromeda.php

Visual approximation (view of the skies and simulation of collision).

http://www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html

http://arxiv.org/pdf/1205.1970.pdf

Just a few questions though. Being noob in cosmology. Is it pertaining to initial computation considering the factor of time/conditions/system/parameter/N-body (timing argument)? Or just an approximation base on movement(local group and getting bigger in our line of sight). And since, we were observing data (photons) that happened 2.5 million years ago. Are there any special consideration(computation) to time or is it included in DL,DA,DC,DT. How did we get such values and are those values referring to actual events(now). Anyone? Thanks in advance.
 
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  • #10


according to my dubious maths, i think andromeda has moved 2.3562 to the 19 km closer to us in the last 2.5 million yrs. can anyone confirm this??
 
  • #11
jonorion said:
according to my dubious maths, i think andromeda has moved 2.3562 to the 19 km closer to us in the last 2.5 million yrs. can anyone confirm this??

How to compute distances below 2 billion light years? Are we supposed to include the tiny value of dark energy or not needed?

Here is the current distance but I'm not sure if it is in realtime or limits of light/time are considered/deducted (I don't know if the values are prior 2.5 million years ago or in real time). Or Messier 110 has been devoured by 'now'(just a thought). Or it is closer than we previously thought (realtime).

http://www.dmuller.net/cosmology/andromeda.php
 
  • #12


jonorion said:
according to my dubious maths, i think andromeda has moved 2.3562 to the 19 km closer to us in the last 2.5 million yrs. can anyone confirm this??
Well let's see my maths also gets dubious with oh so many 0000000000000's, but at a closing speed of 300 km/sec per russ_waters and that website which seems to agree by noting that Andromeda Galaxy is getting 301 km closer to us each and every second of each and every passing day, i get (300 km/s)(3600 s/hr)(24 hr/day)(365.25 day/yr)(2.5 million years) = 2.4(10^16) km. Relativistic effects are minimal at that speed.

At cosmological scales, distances get to be mind-boggling. 2.4(10^16) km is about 2500 light years. So she's 2500 light years closer to us than her observed position. Only minutely closer in the grand scale of things. In another 2.5 billion years, she'll be on our doorstep, although other sites say it is more like 4 billion years, buying us more time to prepare.
 
  • #14


An easy approximation is that 1 km/s for 1 million years is about 1 parsec.

Andromeda Nebula is approaching Sun at a speed of 301 km/s, and that value is known with the precision of +- 1 km/s.

Andromeda Nebula is at a distance of 778 kpc, known with +- 17 kpc.

At that speed, Sun should arrive in 2,6 milliard years.

But the thing is, this is the radial velocity relative to Sun.

Sun is orbiting Milky Way.

Milky Way happens to have rotation plane near Andromeda Nebula.

And Sun happens to be orbiting Milky Way in direction closely approaching Andromeda Nebula.

The orbital speed of Sun around Milky Way is less well known. It turns out that the radial approach speed of Milky Way and Andromeda, as of now, is 109 km/s - with errors +- 4 km/s.

In 100 million years, Sun will have completed half an orbit around Milky Way, and Andromeda Nebula shall be receding at 100 km/h.

Note that within 2,5 million years, the curve of Sun´s orbit will have little effect yet... so the Sun will have approached Andromeda by about 800 pc or 2500 lightyears.

If the mass of Milky Way and Andromeda were negligibly small, then Milky Way and Andromeda should take 7 milliard years to collide - unless they possesses transverse velocity and miss each other.

But the masses are highly unknown. Therefore it is unknown how much Milky Way and Andromeda would accelerate on approach, and when they would have a collision or closest pass.
 
  • #15


Its right here!
 

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  • #17


If anyone gets the program Sandbox Universe, it has a collision between Andromeda and the Milky Way that you can easily load up and watch happen. Pretty neat.
 
  • #18


Universal Sandbox looks very interesting: Thanks for the lead.

A couple of other interesting simulator programs are the Mars24 Sunclock, which tells you the real time on Mars (runs on Java), and Stellarium, which is open source 3D planetarium software program. Both are free.

Download locations.

http://www.giss.nasa.gov/tools/mars24/

and:

http://www.stellarium.org/
 

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