A more detailed reading of the paper now that I’m home from work produces the following:
They project their models forward for the combined Milky Way / Andromeda system, and find that if you assume most available gas in both galaxies will eventually form stars, our solar system comes in at the 39th percentile—about 61% of terrestrial planets are modeled as coming after ours. If in a complication to this model the merger itself pushes some of this gas into a form that can not form stars, we will be further along in the distribution. See http://www.dailygalaxy.com/my_weblog/2014/02/giant-elliptical-galaxies-why-are-they-red-and-dead.html for reasons such an outcome is possible. I might need to pass this onto some of my astronomer friends.
The 8% figure for the whole universe assumes the eventual conversion of all baryonic mass within dark matter haloes into stellar system mass.
This does not fit with my previous reading on the way that star formation apparently shuts down in galaxies over time (quickly for giant ellipticals, slowly for spirals) and data I have seen both elsewhere and in a brief glance at one of their references indicating rapid decay in average star formation rate across the universe over time. Data I have seen elsewhere, covered in my recent astrobiology post, actually supports a rather small amount of additional stars formed over the history of the universe, tapering down slowly and focused in spiral galaxies.
I don’t know if there is a known mechanism that would allow that amount of gas to accrete, and my cursory beginnings of looking at their references digs up a few places indicating that while some of it will probably fall in to the star-forming discs of galaxies in a sufficiently cool state, most of it will probably not be able to contribute to star formation. From one of their references, Adams & Laughlin 1997: “Additional gas can be added to the galaxy through infall onto the galactic disk, but this effect should be relatively small (see the review of Rana, 1991); the total mass added to the disk should not increase the time scale [of star formation] by more than a factor of 2.”
I’m quite confused by all this. Part of this certainly comes from a major difference in approach between this work, which appears to focus on imputing star formation trajectories as galaxies gain mass by comparing galaxies of different sizes, and much previous work I have looked at involving galaxy classification into star-forming and non-star-forming subpopulations across the history of the universe. More digging is required on my part to reconcile all this, and it may be an area of contention. May be worthwhile to dig up some old astronomy friends of mine. Overall though I am rather skeptical of the significance of the 8% figure at this time. Will get back to you after more looking.
A more detailed reading of the paper now that I’m home from work produces the following:
They project their models forward for the combined Milky Way / Andromeda system, and find that if you assume most available gas in both galaxies will eventually form stars, our solar system comes in at the 39th percentile—about 61% of terrestrial planets are modeled as coming after ours. If in a complication to this model the merger itself pushes some of this gas into a form that can not form stars, we will be further along in the distribution. See http://www.dailygalaxy.com/my_weblog/2014/02/giant-elliptical-galaxies-why-are-they-red-and-dead.html for reasons such an outcome is possible. I might need to pass this onto some of my astronomer friends.
The 8% figure for the whole universe assumes the eventual conversion of all baryonic mass within dark matter haloes into stellar system mass.
This does not fit with my previous reading on the way that star formation apparently shuts down in galaxies over time (quickly for giant ellipticals, slowly for spirals) and data I have seen both elsewhere and in a brief glance at one of their references indicating rapid decay in average star formation rate across the universe over time. Data I have seen elsewhere, covered in my recent astrobiology post, actually supports a rather small amount of additional stars formed over the history of the universe, tapering down slowly and focused in spiral galaxies.
I don’t know if there is a known mechanism that would allow that amount of gas to accrete, and my cursory beginnings of looking at their references digs up a few places indicating that while some of it will probably fall in to the star-forming discs of galaxies in a sufficiently cool state, most of it will probably not be able to contribute to star formation. From one of their references, Adams & Laughlin 1997: “Additional gas can be added to the galaxy through infall onto the galactic disk, but this effect should be relatively small (see the review of Rana, 1991); the total mass added to the disk should not increase the time scale [of star formation] by more than a factor of 2.”
I’m quite confused by all this. Part of this certainly comes from a major difference in approach between this work, which appears to focus on imputing star formation trajectories as galaxies gain mass by comparing galaxies of different sizes, and much previous work I have looked at involving galaxy classification into star-forming and non-star-forming subpopulations across the history of the universe. More digging is required on my part to reconcile all this, and it may be an area of contention. May be worthwhile to dig up some old astronomy friends of mine. Overall though I am rather skeptical of the significance of the 8% figure at this time. Will get back to you after more looking.