Timeline for Stellar outflows in the Milky Way
Current License: CC BY-SA 3.0
19 events
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| Jun 11, 2020 at 9:33 | history | edited | CommunityBot |
Commonmark migration
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| Mar 10, 2015 at 10:32 | comment | added | user32023 | Thanks for the additional editorial. I'm not looking to draw conclusions just yet, I'm just wondering whether we have enough objective data to say whether there's a net inflow or outflow (or we just don't know). With regard to the additional issues you mentioned about what could cause such a drift of primarily type I stars, I would offer the recent collision with Sat. DET as an example of a force that could pull the bulge gases outward. Most spiral galaxies are thought to have their source in a collision of some sort. | |
| Mar 10, 2015 at 9:22 | history | edited | ProfRob | CC BY-SA 3.0 |
added 1529 characters in body; Post Made Community Wiki
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| Mar 10, 2015 at 1:42 | comment | added | user32023 | @RobJefferies Then we're back to my original question: how do we know (or do we know) whether the net flow is inward, outward or closed? I can reference several computer simulations that show massive streams of ejecta and infalling matter after a collision and we've collided with Sag. DET. as recently as a billion years ago. | |
| Mar 10, 2015 at 0:37 | comment | added | ProfRob | @DonaldRoyAirey It does not. The Sun moves on an approximately circular orbit and executes radial epicycles with a period of about 150 million years. You cannot extrapolate numbers like this backwards and forwards as you are doing. | |
| Mar 10, 2015 at 0:26 | comment | added | user32023 | I agree with your interpretation of the papers but not in your final conclusion. A 'small' drift of 10 km/s means that 1 billion years ago, our sun was 10 kpc further out, beyond the rim and into the halo. It means that in 850 million years, we'll have drifted into the galactic core. This is not a small 'drift'. | |
| Mar 5, 2015 at 22:28 | history | edited | ProfRob | CC BY-SA 3.0 |
added solar motion link
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| Mar 5, 2015 at 22:10 | comment | added | user32023 | Is this the document you're referencing above? arxiv.org/abs/1209.0759 | |
| Mar 5, 2015 at 15:02 | history | edited | ProfRob | CC BY-SA 3.0 |
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| Mar 5, 2015 at 1:37 | comment | added | user32023 | thanks for the charts. I found that study but was unable to parse the chart (in layman's terms). They seem to be giving the velocities relative to Earth. That is, are we looking at radial velocities from the galactic center (similar to your first chart), or are we just looking at the relative flow from Earth? | |
| Mar 5, 2015 at 1:07 | comment | added | ProfRob | @DonaldRoyAirey I invite everyone to look at what you are looking at. The diagram is a rotation curve for the galaxy. Superposed on this is a blue non-Keplerian curve - that looks nothing like $v \propto r^{-1/2}$. The text clearly states "A Galaxy is a bit more complicated. Since there's not just one big mass at the center, the rotation curve should look different [from Keplerian] than that of the Solar System." , and goes on to explain how to calculate the curve properly in the case of mass follows light. I have edited my answer to add the radial information you require. No outflows. | |
| Mar 5, 2015 at 0:57 | history | edited | ProfRob | CC BY-SA 3.0 |
added material about radial disk velocities.
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| Mar 5, 2015 at 0:30 | comment | added | user32023 | Using the link you provided, scroll about 2/3 of the way through the page. There you see a diagram of the rotational velocities in the Milky Way. The blue line is the Kepler prediction, the green line is the observed velocities. How can you disagree when the very first article you Googled has the Kepler velocity curve? | |
| Mar 5, 2015 at 0:02 | comment | added | ProfRob | @DonaldRoyAirey I also disagree even that most explanations come with a diagram with the Kepler prediction superimposed. I just googled "rotation curve of Milky way" and followed the first image that came up on milkyway.cs.rpi.edu/milkyway/science.php Even this layperson's description correctly explains that we do not expect a strictly Keplerian curve. | |
| Mar 4, 2015 at 23:56 | comment | added | ProfRob | @DonaldRoyAirey I have answered several similar queries in the last few weeks. Arguments like this are presented to simplify the discussion (usually for the layperson). A Keplerian orbit has all the mass concentrated at the centre so cannot be applied unless this is the case (or for a spherically symmetric mass distribution). It is approximately true for the case of the Galaxy if mass were to follow light. Real work uses real potentials and if not it should be criticised. [And it's $v \propto (M/r)^{1/2}$.] | |
| Mar 4, 2015 at 22:23 | comment | added | user32023 | Radial, meaning in the direction of the radius of the main disk. I'm not an expert either but I know that the general logic goes like this: the stars in the disk should obey Kepler's laws, however, they're traveling much faster than predictions based on the visible mass of the galaxy. If the stars are falling in or falling out, then we can't use the simple relation:$$ f(v) = \sqrt{GM/r^2}. $$when predicting the rotational velocity of a star at a given radius, r. Every description I've seen of the missing mass issue comes with a diagram of the Kepler prediction to highlight the missing mass. | |
| Mar 4, 2015 at 22:08 | comment | added | ProfRob | "Radial direction of the disk"? Galactic outflows are perpendicular to the disk. I am no great expert, but I doubt that any serious work on dark matter relies on Kepler's laws at all, as it is not valid for a distribution of gravitating matter. What size of radial motions were you thinking of? We know indeed that the motion of gas and stars in the disk is mostly circular. | |
| Mar 4, 2015 at 21:52 | comment | added | user32023 | This is much closer to what I'm looking for, but, as you guessed, for the radial direction of the main disk. Here's the exact issue: our assumptions about Dark Matter are based on the observation of a rotational velocity and an assumption about a stable orbit (Kepler's laws only apply to stable orbits). So somewhere there must be a definitive study showing that there's no radial component (either inward or outward) in order to support the current calculations for the Dark Matter mass of our galaxy. I'm wondering where that data might be. | |
| Mar 4, 2015 at 21:44 | history | answered | ProfRob | CC BY-SA 3.0 |