How big is the Milky Way?

[brellis]

Recently, red giants were discovered 500,000 light years from the core of the Andromeda Galaxy, making it much bigger than previously thought. Today, this bbc article suggests the Magellanic Clouds are not likely to be bound by the Milky Way, because it's not big enough. Could there be unseen stars orbiting the Milky Way from distances beyond our current estimate, restoring the Mag. Clouds to companion status? <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000"><em><strong>I'm a recovering optimist - things could be better.</strong></em></font> </p> </div>

 

[tfwthom]

Every thing you want to know about The Local Group of Galaxies <br /> <div class="Discussion_UserSignature"> <font size="1" color="#3366ff">www.siriuslookers.org</font> </div>

 

[dragon04]

I guess in a way, it's a matter of semantics. <br /><br /><font color="yellow">Today, this bbc article suggests the Magellanic Clouds are not likely to be bound by the Milky Way, because it's not big enough. Could there be unseen stars orbiting the Milky Way from distances beyond our current estimate, restoring the Mag. Clouds to companion status?</font><br /><br />Let's work with an object that is at least one solar mass and then determine the needed velocity required for its gravitational capture by the Milky Way.<br /><br />One could argue that this would be the maximum "diameter" of the galaxy.<br /><br />In regards to the Magellanic Clouds, it should be easy enough to calculate their velocities and vectors (with sufficient resolution) and apply orbital mechanics to determine if they are moving towards, away, or in orbit of the galaxy, I'd think.<br /><br />There have been documented cases of stars being "ejected" from the Galaxy, so I'd think it logically would follow that we could determine whether our companion "galaxies" were here to stay, or just passersby.<br /> <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

 

[nexium]

Let'assume that Andromeda has 4 times the mass of our galaxy, but it is twice as far from the Magenellic Clouds. The gravity would be equal, and the clouds would orbit neither. Amdromedia is lots more than twice the distance, so there is presently nothing (we know of) other than our galaxy for the Maginellic Clouds to orbit. That may change in a few million years, and is likely to change in a few billion years.<br />Black holes up to 1000 solar mass may orbit 100,000 light years to one million light years from the center of our galaxy, but these would not add much mass to our galaxy unless there are millions of these black holes. Neil

 

[brellis]

Thanks for the reference. It's helpful to know that while the Andromeda Galaxy is similar to the Milky Way, it has been estimated to be larger than the Milky Way but less dense. As we're better able to observe Andromeda than our own Galaxy, we can [finally] see the elusive "stellar halo" of red giants surrounding Andromeda.<br /><br />To rephrase my original question: does the confirmation of the stellar halo change the math as to the Mass of Andromeda? Can we assume a similar stellar halo exists unseen around our Milky Way, and if we make that assumption, would that affect calculations recently published that place the Magellanic Cloud in "passerby" status in relation to our Milky Way? <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000"><em><strong>I'm a recovering optimist - things could be better.</strong></em></font> </p> </div>

 

[brellis]

hi steve, thanks for the post.<br /><br />in another article on the stellar halo observations, they said that if you could see with the naked eye what they've measured with spectograph, Andromeda would appear as large as the Big Dipper! They also said that Andromeda and the Milky Way were affecting objects so far away from their centers that the two Galaxies were practically touching. <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000"><em><strong>I'm a recovering optimist - things could be better.</strong></em></font> </p> </div>

 

[tropicalzone]

approx 100,000 light years across