MilkyWay@home: Difference between revisions

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== Methods ==

MilkyWay@home studies the history of our galaxy by analyzing the stars in the Milky Way galaxy's '''''[[wikipedia:Galactic_halo|Galactic Halo]]'''''. This includes searching for elusive '''''[[wikipedia:Dark_matter|dark matter]]'''''. This research is done by mapping structures of stars orbiting the Milky Way - many these structures are actually "tidal debris streams," or dwarf galaxies that are being pulled apart by our Galaxy's superior gravitational field. The orbits, shapes, and compositions of these dwarf galaxies provide vital clues to the history of our Galaxy, as well as to the distribution of dark matter. The "N-body" project of MilkyWay@home creates simulated dwarf galaxies and "shoots" them into the Milky Way's gravitational field. We allow the simulated dwarf galaxy's initial conditions to vary until the final simulated dwarf matches what we see in actual halo structures. In other words, we are trying to match dwarf galaxy models to real data, in order to learn more about what is (and what isn't) possible for our Galaxy~~. We use data from the '''''[[wikipedia:Sloan_Digital_Sky_Survey|Sloan Digital Sky Survey]].[https://milkyway.cs.rpi.edu/milkyway/science.php]'''''~~

MilkyWay@home studies the history of our galaxy by analyzing the stars in the Milky Way galaxy's '''''[[wikipedia:Galactic_halo|Galactic Halo]]'''''. This includes searching for elusive '''''[[wikipedia:Dark_matter|dark matter]]'''''. This research is done by mapping structures of stars orbiting the Milky Way - many these structures are actually "tidal debris streams," or dwarf galaxies that are being pulled apart by our Galaxy's superior gravitational field. The orbits, shapes, and compositions of these dwarf galaxies provide vital clues to the history of our Galaxy, as well as to the distribution of dark matter. The "N-body" sub-project of MilkyWay@home creates simulated dwarf galaxies and "shoots" them into the Milky Way's gravitational field. We allow the simulated dwarf galaxy's initial conditions to vary until the final simulated dwarf matches what we see in actual halo structures. In other words, we are trying to match dwarf galaxy models to real data, in order to learn more about what is (and what isn't) possible for our Galaxy.

Using stellar data from the Sloan Digital Sky Survey (SDSS) and the Dark Energy Camera (DEC), we were able to use MilkyWay@home's N-body project to generate a mass estimate of the Orphan-Cehnab's original progenitor dwarf galaxy, the first time such an estimate has ever been made from tidal debris alone. The Orphan-Chenab Stream (OCS) is a tidal stream that was discovered in 2006 while examining the Sagittarius Stream. Because no progenitor core could be detected within the stream, it was originally named the 'Orphan Stream'. However, in 2018, the southern half of the stream was detected and named Chenab. Thus, the stream was renamed 'Orphan-Chenab'.

We found the total mass of the OCS's progenitor to be roughly 2 x 107 solar masses, with a mass-to-light ratio of 73.5 (about 98.6% dark matter). This is interesting because other mass estiamtes of the OCS progenitor placed this value somewhere between 108 and 109 solar masses. This is likely because these mass estimates used velocity dispersions for their calculation and assumed the system to be in equilibrium. However, we have also shown that the OCS has an unbound and heavily disrupted progenitor, shattering any assumption of dynamic equilibrium. We also find that the majority of the OCS's mass (especially its dark matter) resides within the tails of the stream, making them ideal candidates for indirect dark matter detection experiments.

It should still be noted, however, that this measurement is incomplete as our optimizations using MilkyWay@home require an in-depth analysis of the sources of systematic error, such as the accuracy of our Milky Way gravitational potential and the validity of our progenitor models. We also need to include the effects of the Large Magellanic Cloud as it was shown in 2019 to have a measurable effect on the Southern tail of the OCS (Erkal et. al. 2019). In future work, we plan on quantifying this systematic error as the effects of different galactic models on our final fitted mass.

== Project team / Sponsors ==

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 == Methods ==
-MilkyWay@home studies the history of our galaxy by analyzing the stars in the Milky Way galaxy's '''''[[wikipedia:Galactic_halo|Galactic Halo]]'''''. This includes searching for elusive '''''[[wikipedia:Dark_matter|dark matter]]'''''. This research is done by mapping structures of stars orbiting the Milky Way - many these structures are actually "tidal debris streams," or dwarf galaxies that are being pulled apart by our Galaxy's superior gravitational field. The orbits, shapes, and compositions of these dwarf galaxies provide vital clues to the history of our Galaxy, as well as to the distribution of dark matter. The "N-body" project of MilkyWay@home creates simulated dwarf galaxies and "shoots" them into the Milky Way's gravitational field. We allow the simulated dwarf galaxy's initial conditions to vary until the final simulated dwarf matches what we see in actual halo structures. In other words, we are trying to match dwarf galaxy models to real data, in order to learn more about what is (and what isn't) possible for our Galaxy.  We use data from the '''''[[wikipedia:Sloan_Digital_Sky_Survey|Sloan Digital Sky Survey]].[https://milkyway.cs.rpi.edu/milkyway/science.php]'''''
+MilkyWay@home studies the history of our galaxy by analyzing the stars in the Milky Way galaxy's '''''[[wikipedia:Galactic_halo|Galactic Halo]]'''''. This includes searching for elusive '''''[[wikipedia:Dark_matter|dark matter]]'''''. This research is done by mapping structures of stars orbiting the Milky Way - many these structures are actually "tidal debris streams," or dwarf galaxies that are being pulled apart by our Galaxy's superior gravitational field. The orbits, shapes, and compositions of these dwarf galaxies provide vital clues to the history of our Galaxy, as well as to the distribution of dark matter. The "N-body" sub-project of MilkyWay@home creates simulated dwarf galaxies and "shoots" them into the Milky Way's gravitational field. We allow the simulated dwarf galaxy's initial conditions to vary until the final simulated dwarf matches what we see in actual halo structures. In other words, we are trying to match dwarf galaxy models to real data, in order to learn more about what is (and what isn't) possible for our Galaxy.
-Using stellar data from the Sloan Digital Sky Survey (SDSS) and the Dark Energy Camera (DEC), we were able to use MilkyWay@home's N-body project to generate a mass estimate of the Orphan-Cehnab's original progenitor dwarf galaxy, the first time such an estimate has ever been made from tidal debris alone. The Orphan-Chenab Stream (OCS) is a tidal stream that was discovered in 2006 while examining the Sagittarius Stream. Because no progenitor core could be detected within the stream, it was originally named the 'Orphan Stream'. However, in 2018, the southern half of the stream was detected and named Chenab. Thus, the stream was renamed 'Orphan-Chenab'.
-We found the total mass of the OCS's progenitor to be roughly 2 x 107 solar masses, with a mass-to-light ratio of 73.5 (about 98.6% dark matter). This is interesting because other mass estiamtes of the OCS progenitor placed this value somewhere between 108 and 109 solar masses. This is likely because these mass estimates used velocity dispersions for their calculation and assumed the system to be in equilibrium. However, we have also shown that the OCS has an unbound and heavily disrupted progenitor, shattering any assumption of dynamic equilibrium. We also find that the majority of the OCS's mass (especially its dark matter) resides within the tails of the stream, making them ideal candidates for indirect dark matter detection experiments.
-It should still be noted, however, that this measurement is incomplete as our optimizations using MilkyWay@home require an in-depth analysis of the sources of systematic error, such as the accuracy of our Milky Way gravitational potential and the validity of our progenitor models. We also need to include the effects of the Large Magellanic Cloud as it was shown in 2019 to have a measurable effect on the Southern tail of the OCS (Erkal et. al. 2019). In future work, we plan on quantifying this systematic error as the effects of different galactic models on our final fitted mass.
 == Project team / Sponsors ==