BRaTS@Home - Revision history

Al Piskun: images

2026-08-20T19:44:21Z

images

← Older revision		Revision as of 19:44, 20 August 2026
Line 42:		Line 42:

	=== Origins and launch (2007) ===		=== Origins and launch (2007) ===

	[[File:UMSL 01.jpg\|thumb\|upright=1.2\|right\|The University of Missouri-St. Louis, which hosted BRaTS@Home in a physics department lab.\|alt=Aerial view of a university campus with modern buildings and ponds]]

	BRaTS@Home was created by David Coss, a physics graduate student at UMSL working under professor Ricardo Flores on the simulation of gravitational lensing.<ref name=nasa2008>{{cite conference \|last1=Coss \|first1=David \|title=Simulation of Gravitational Lensing \|conference=NASA Missouri Space Grant Consortium Annual Meeting \|location=Missouri, USA \|date=April 2008 \|publisher=NASA Missouri Space Grant Consortium \|url=http://research.davecoss.com/nasa_mo_paper.pdf \|access-date=August 20, 2026 \|archive-url=https://web.archive.org/web/20080827225312/http://research.davecoss.com/nasa_mo_paper.pdf \|archive-date=August 27, 2008 \|url-status=dead}}</ref> Computing deflection angles by direct integration for realistic cluster mass distributions is computationally expensive, so rather than buy time on a conventional cluster, Coss turned to [[wikipedia:BOINC\|BOINC]], which "allows scientists to build a computer cluster at the price of one server" by harvesting the idle time of volunteers' computers.<ref name=aas/>		BRaTS@Home was created by David Coss, a physics graduate student at UMSL working under professor Ricardo Flores on the simulation of gravitational lensing.<ref name=nasa2008>{{cite conference \|last1=Coss \|first1=David \|title=Simulation of Gravitational Lensing \|conference=NASA Missouri Space Grant Consortium Annual Meeting \|location=Missouri, USA \|date=April 2008 \|publisher=NASA Missouri Space Grant Consortium \|url=http://research.davecoss.com/nasa_mo_paper.pdf \|access-date=August 20, 2026 \|archive-url=https://web.archive.org/web/20080827225312/http://research.davecoss.com/nasa_mo_paper.pdf \|archive-date=August 27, 2008 \|url-status=dead}}</ref> Computing deflection angles by direct integration for realistic cluster mass distributions is computationally expensive, so rather than buy time on a conventional cluster, Coss turned to [[wikipedia:BOINC\|BOINC]], which "allows scientists to build a computer cluster at the price of one server" by harvesting the idle time of volunteers' computers.<ref name=aas/>
Line 52:		Line 50:

	=== Operation (2007 to 2010) ===		=== Operation (2007 to 2010) ===

	[[File:BOINC_manager_screenshot.jpg\|thumb\|upright=1.2\|left\|A BOINC client attaching to projects; BRaTS@Home participants attached by entering the project URL in the BOINC manager.\|alt=Screenshot of BOINC manager software]]

	The project was hosted on a computer named ''maxwell'' in a UMSL lab, reachable at the address <code>http://maxwell.dhcp.umsl.edu/brats/</code>.<ref name=home2010>{{cite web \|url=http://maxwell.dhcp.umsl.edu/brats/index.php \|title=BRaTS@Home homepage (capture of 25 March 2010) \|publisher=University of Missouri-St. Louis \|access-date=August 20, 2026 \|archive-url=http://web.archive.org/web/20100325212718/http://maxwell.dhcp.umsl.edu:80/brats/index.php \|archive-date=March 25, 2010 \|url-status=dead}}</ref> Being tied to a campus network had its hazards, and the news archive chronicles a colorful series of interruptions: campus-wide power outages, a router and firewall failure that removed the whole campus from the Internet, an unannounced firewall change that forced a hiatus in early 2008 (used as an opportunity to upgrade to a newer BOINC server), and backbone upgrades by the campus Internet provider.<ref name=oldnews/><ref name=allnews/><ref name=home2009/>		The project was hosted on a computer named ''maxwell'' in a UMSL lab, reachable at the address <code>http://maxwell.dhcp.umsl.edu/brats/</code>.<ref name=home2010>{{cite web \|url=http://maxwell.dhcp.umsl.edu/brats/index.php \|title=BRaTS@Home homepage (capture of 25 March 2010) \|publisher=University of Missouri-St. Louis \|access-date=August 20, 2026 \|archive-url=http://web.archive.org/web/20100325212718/http://maxwell.dhcp.umsl.edu:80/brats/index.php \|archive-date=March 25, 2010 \|url-status=dead}}</ref> Being tied to a campus network had its hazards, and the news archive chronicles a colorful series of interruptions: campus-wide power outages, a router and firewall failure that removed the whole campus from the Internet, an unannounced firewall change that forced a hiatus in early 2008 (used as an opportunity to upgrade to a newer BOINC server), and backbone upgrades by the campus Internet provider.<ref name=oldnews/><ref name=allnews/><ref name=home2009/>
Line 66:		Line 62:

	The scheduler was shut down on April 13, 2010, and volunteers were asked to detach from the project by mid-May 2010, when the university was expected to switch off the server.<ref name=shutdown>{{cite web \|url=http://maxwell.dhcp.umsl.edu/brats/forum_thread.php?id=183 \|title=Scheduler Shutdown (news thread, capture of 17 April 2010) \|publisher=BRaTS@Home message boards \|access-date=August 20, 2026 \|archive-url=http://web.archive.org/web/20100417122439/http://maxwell.dhcp.umsl.edu:80/brats/forum_thread.php?id=183 \|archive-date=April 17, 2010 \|url-status=dead}}</ref> The final statistics export seen by BOINCstats is dated April 12, 2010, and records 79,464 total credits granted to 115 users and 492 host computers, with 45 teams.<ref name=boincstats/> Coss received his Ph.D. in physics in 2010,<ref name=cv>{{cite web \|url=http://davecoss.com/cv.pdf \|title=Curriculum Vitae of David Coss, Ph.D. \|website=davecoss.com \|access-date=August 20, 2026}}</ref> and mirrored the site's content at research.davecoss.com as a keepsake before the original server went dark.<ref name=wind-down/>		The scheduler was shut down on April 13, 2010, and volunteers were asked to detach from the project by mid-May 2010, when the university was expected to switch off the server.<ref name=shutdown>{{cite web \|url=http://maxwell.dhcp.umsl.edu/brats/forum_thread.php?id=183 \|title=Scheduler Shutdown (news thread, capture of 17 April 2010) \|publisher=BRaTS@Home message boards \|access-date=August 20, 2026 \|archive-url=http://web.archive.org/web/20100417122439/http://maxwell.dhcp.umsl.edu:80/brats/forum_thread.php?id=183 \|archive-date=April 17, 2010 \|url-status=dead}}</ref> The final statistics export seen by BOINCstats is dated April 12, 2010, and records 79,464 total credits granted to 115 users and 492 host computers, with 45 teams.<ref name=boincstats/> Coss received his Ph.D. in physics in 2010,<ref name=cv>{{cite web \|url=http://davecoss.com/cv.pdf \|title=Curriculum Vitae of David Coss, Ph.D. \|website=davecoss.com \|access-date=August 20, 2026}}</ref> and mirrored the site's content at research.davecoss.com as a keepsake before the original server went dark.<ref name=wind-down/>

			[[File:UMSL 01.jpg\|thumb\|The University of Missouri-St. Louis, which hosted BRaTS@Home in a physics department lab.\|alt=Aerial view of a university campus with modern buildings and ponds\|350x350px]]

	== Science ==		== Science ==

	=== Gravitational lensing ===		=== Gravitational lensing ===

	[[File:Horseshoe_Einstein_Ring_from_Hubble.jpg\|thumb\|upright=1.25\|right\|Gravitational lensing in the real universe: the Hubble Space Telescope imaged a distant galaxy (blue) bent into a near-complete ring by the gravity of a foreground red galaxy.\|alt=Hubble telescope image of a blue galaxy forming a horseshoe-shaped ring around a red galaxy]]

	[[wikipedia:Gravitational lensing\|Gravitational lensing]] is the deflection of light by gravity. A point mass <math>M</math> deflects a light ray passing at impact parameter <math>b</math> by the angle		[[wikipedia:Gravitational lensing\|Gravitational lensing]] is the deflection of light by gravity. A point mass <math>M</math> deflects a light ray passing at impact parameter <math>b</math> by the angle
Line 102:		Line 98:

	where <math>\phi_\ell</math> is the polar angle of the Fourier mode <math>\boldsymbol{\ell}</math>; Coss's 2009 consortium paper examined the limitations and artifacts inherent in such FFT-based convolution calculations.<ref name=nasa2009/>		where <math>\phi_\ell</math> is the polar angle of the Fourier mode <math>\boldsymbol{\ell}</math>; Coss's 2009 consortium paper examined the limitations and artifacts inherent in such FFT-based convolution calculations.<ref name=nasa2009/>

			[[File:Bullet cluster lensing.jpg\|thumb\|Weak gravitational lensing maps the invisible: in the Bullet Cluster, lensing-derived mass (blue) is offset from the hot gas (red), evidence that most of the cluster's mass is dark matter. BRaTS@Home studied how cluster shape and substructure affect weak-lensing shear signals.\|alt=Astronomical image of two colliding galaxy clusters with overlaid mass contours\|350x350px]]

	=== Results ===		=== Results ===

	[[File:Bullet cluster lensing.jpg\|thumb\|upright=1.25\|left\|Weak gravitational lensing maps the invisible: in the Bullet Cluster, lensing-derived mass (blue) is offset from the hot gas (red), evidence that most of the cluster's mass is dark matter. BRaTS@Home studied how cluster shape and substructure affect weak-lensing shear signals.\|alt=Astronomical image of two colliding galaxy clusters with overlaid mass contours]]

	The analysis showed that average shear measured inside and outside half the [[wikipedia:Virial radius\|virial radius]] of the simulated clusters displays a distinct dispersion, varying by 24 percent from the mean across the 21 maps, while the estimated numerical error is of order 5 percent, meaning the dispersion is a reliable physical consequence of the clusters' shape differences. It correlates most strongly with the ratio of smallest-to-largest principal axis lengths of a cluster's isodensity shell. Image ellipticities, important for mass reconstruction, showed very little variance, but the tangential alignment of the average image distortion was strong enough that the locations of mass density peaks were easily resolvable.<ref name=thesis/> In short, the volunteers' computers helped establish how the shapes and substructure of dark matter halos imprint themselves on weak-lensing observables.		The analysis showed that average shear measured inside and outside half the [[wikipedia:Virial radius\|virial radius]] of the simulated clusters displays a distinct dispersion, varying by 24 percent from the mean across the 21 maps, while the estimated numerical error is of order 5 percent, meaning the dispersion is a reliable physical consequence of the clusters' shape differences. It correlates most strongly with the ratio of smallest-to-largest principal axis lengths of a cluster's isodensity shell. Image ellipticities, important for mass reconstruction, showed very little variance, but the tangential alignment of the average image distortion was strong enough that the locations of mass density peaks were easily resolvable.<ref name=thesis/> In short, the volunteers' computers helped establish how the shapes and substructure of dark matter halos imprint themselves on weak-lensing observables.

Al Piskun: Created page with "{{Infobox software | name = BRaTS@Home | logo = | logo caption = | screenshot = | caption = A simulated lensed image of M31 produced with BRaTS ray tracing | description = BRaTS@Home was a completed Astrophysics BOINC project that used volunteer computers to perform gravitational lensing ray-tracing simulations of galaxy clusters, developed by David Coss and sponsored by the University of Missouri..."

2026-08-20T19:38:37Z

Created page with "{{Infobox software | name = BRaTS@Home | logo = | logo caption = | screenshot = | caption = A simulated lensed image of M31 produced with BRaTS ray tracing | description = BRaTS@Home was a completed Astrophysics BOINC project that used volunteer computers to perform gravitational lensing ray-tracing simulations of galaxy clusters, developed by David Coss and sponsored by the University of Missouri..."

New page

{{Infobox software
| name = BRaTS@Home
| logo =
| logo caption =
| screenshot =
| caption = A simulated lensed image of M31 produced with BRaTS ray tracing
| description = BRaTS@Home was a completed Astrophysics BOINC project that used volunteer computers to perform gravitational lensing ray-tracing simulations of galaxy clusters, developed by David Coss and sponsored by the University of Missouri-St. Louis.
| status = Completed
| category = Astrophysics
| compute = CPU
| dependencies = [[wikipedia:BOINC|BOINC]] client
| developer = David Coss
| author = David Coss
| sponsor = University of Missouri-St. Louis
| maintainer = None (project completed 2010)
| released = {{Start date and age|2007|06|05}}
| completed = {{Start date and age|2010|04|13}} (scheduler shut down; website offline by mid-May 2010)
| discontinued =
| repository = {{URL|https://github.com/kd0kfo/cosmology}}
| programming language = C++
| operating system = Windows, Linux
| size =
| stats as of = April 12, 2010 (final statistics export)
| average performance = ~1.1 GFLOPS (average, June 2007 to April 2008)
| active users = 0 (at final export)
| total users = 115
| active hosts = 0 (at final export)
| total hosts = 492
| rac = 0 (at final export)
| credit per day =
| gpu performance = Not applicable (CPU only)
| cpu performance = ~1.1 GFLOPS average (June 2007 to April 2008)
| website = {{URL|http://maxwell.dhcp.umsl.edu/brats/}} (offline; archived)
| license = GPL-3.0 (successor CosApps code)
}}

'''BRaTS@Home''' was a [[wikipedia:Volunteer computing|volunteer computing]] project built on the [[wikipedia:BOINC|BOINC]] (Berkeley Open Infrastructure for Network Computing) platform that performed [[wikipedia:Gravitational lensing|gravitational lensing]] ray-tracing simulations. The name is a [[wikipedia:Recursive acronym|recursive acronym]]: '''BRaTS''' stands for ''BRaTS Ray Trace Simulator''.<ref name=home2009>{{cite web |url=http://maxwell.dhcp.umsl.edu/brats/ |title=BRaTS@Home homepage (capture of 22 March 2009) |publisher=University of Missouri-St. Louis |access-date=August 20, 2026 |archive-url=https://web.archive.org/web/20090322190553/http://maxwell.dhcp.umsl.edu/brats/ |archive-date=March 22, 2009 |url-status=dead}}</ref> The project simulated the way [[wikipedia:Dark matter|dark matter]] in [[wikipedia:Galaxy cluster|galaxy clusters]] and other foreground mass concentrations distorts the images of more distant background objects, work that formed the computational core of developer David Coss's doctoral research at the [[wikipedia:University of Missouri-St. Louis|University of Missouri-St. Louis]] (UMSL).<ref name=thesis>{{cite thesis |last1=Coss |first1=David |title=Weak shear study of galaxy clusters by simulated gravitational lensing |type=Ph.D. thesis |institution=University of Missouri-St. Louis |date=2010 |bibcode=2010PhDT.......285C |url=https://ui.adsabs.harvard.edu/abs/2010PhDT.......285C/abstract |access-date=August 20, 2026}}</ref>

BRaTS@Home went online on June 5, 2007 and ran for almost three years, attracting volunteers from 26 countries before being retired in April 2010 upon the successful defense of Coss's dissertation.<ref name=aas>{{cite conference |last1=Coss |first1=David Raymond |last2=Flores |first2=R. |title=BRaTS@Home and BOINC Distributed Computing for Parallel Computation |conference=212th Meeting of the American Astronomical Society |location=St. Louis, Missouri |date=June 2-5, 2008 |bibcode=2008AAS...212.2410C |url=https://ui.adsabs.harvard.edu/abs/2008AAS...212.2410C/abstract |access-date=August 20, 2026}}</ref><ref name=wind-down>{{cite web |url=http://maxwell.dhcp.umsl.edu/brats/forum_thread.php?id=182 |title=Project Status (project news forum thread, capture of 27 March 2010) |publisher=BRaTS@Home message boards |access-date=August 20, 2026 |archive-url=http://web.archive.org/web/20100327131814/http://maxwell.dhcp.umsl.edu:80/brats/forum_thread.php?id=182 |archive-date=March 27, 2010 |url-status=dead}}</ref> It is remembered as a small, personable project: run single-handedly by a graduate student from a lab computer, invitation-only for most of its life, and famous among its participants for the occasional campus power outage that briefly silenced the server.<ref name=home2009/><ref name=poweroutage>{{cite web |url=http://maxwell.dhcp.umsl.edu/brats/forum_thread.php?id=179 |title=Power Outage (news thread, capture of 27 March 2010) |publisher=BRaTS@Home message boards |access-date=August 20, 2026 |archive-url=http://web.archive.org/web/20100327131545/http://maxwell.dhcp.umsl.edu:80/brats/forum_thread.php?id=179 |archive-date=March 27, 2010 |url-status=dead}}</ref>

== History ==

=== Origins and launch (2007) ===

[[File:UMSL 01.jpg|thumb|upright=1.2|right|The University of Missouri-St. Louis, which hosted BRaTS@Home in a physics department lab.|alt=Aerial view of a university campus with modern buildings and ponds]]

BRaTS@Home was created by David Coss, a physics graduate student at UMSL working under professor Ricardo Flores on the simulation of gravitational lensing.<ref name=nasa2008>{{cite conference |last1=Coss |first1=David |title=Simulation of Gravitational Lensing |conference=NASA Missouri Space Grant Consortium Annual Meeting |location=Missouri, USA |date=April 2008 |publisher=NASA Missouri Space Grant Consortium |url=http://research.davecoss.com/nasa_mo_paper.pdf |access-date=August 20, 2026 |archive-url=https://web.archive.org/web/20080827225312/http://research.davecoss.com/nasa_mo_paper.pdf |archive-date=August 27, 2008 |url-status=dead}}</ref> Computing deflection angles by direct integration for realistic cluster mass distributions is computationally expensive, so rather than buy time on a conventional cluster, Coss turned to [[wikipedia:BOINC|BOINC]], which "allows scientists to build a computer cluster at the price of one server" by harvesting the idle time of volunteers' computers.<ref name=aas/>

The project came online on June 5, 2007, initially offering work for [[wikipedia:Linux|Linux]] on x86 computers only.<ref name=oldnews>{{cite web |url=http://maxwell.dhcp.umsl.edu/brats/old_news.php |title=BRaTS@Home news archive (capture of 22 October 2007) |publisher=BRaTS@Home |access-date=August 20, 2026 |archive-url=http://web.archive.org/web/20071022170116/http://maxwell.dhcp.umsl.edu:80/brats/old_news.php |archive-date=October 22, 2007 |url-status=dead}}</ref> The first successful work unit was completed the following day.<ref name=oldnews/> The project carried an "alpha testing" label from June 13, 2007, and the first small [[wikipedia:Microsoft Windows|Windows]] (Windows XP) work units went out on June 18.<ref name=oldnews/> On July 17, 2007, Coss removed the beta label, writing that "things are running smoothly and I am at a point where science can be done."<ref name=oldnews/> The statistics service BOINCstats first recorded the project on June 25, 2007.<ref name=boincstats>{{cite web |url=https://www.boincstats.com/stats/48/project/detail |title=BRaTS@Home - Detailed stats |website=BOINCstats/BAM! |access-date=August 20, 2026}}</ref>

From early on, enrollment was restricted: new accounts required an invitation code, a state of affairs still in effect as late as 2009.<ref name=home2009/> The demand for codes grew so heavy that Coss removed his email address from the front page, directing volunteers to the message boards instead.<ref name=allnews>{{cite web |url=http://maxwell.dhcp.umsl.edu/brats/all_news.php |title=BRaTS@Home news archive (capture of 2 February 2008) |publisher=BRaTS@Home |access-date=August 20, 2026 |archive-url=http://web.archive.org/web/20080202130300/http://maxwell.dhcp.umsl.edu:80/brats/all_news.php |archive-date=February 2, 2008 |url-status=dead}}</ref>

=== Operation (2007 to 2010) ===

[[File:BOINC_manager_screenshot.jpg|thumb|upright=1.2|left|A BOINC client attaching to projects; BRaTS@Home participants attached by entering the project URL in the BOINC manager.|alt=Screenshot of BOINC manager software]]

The project was hosted on a computer named ''maxwell'' in a UMSL lab, reachable at the address <code>http://maxwell.dhcp.umsl.edu/brats/</code>.<ref name=home2010>{{cite web |url=http://maxwell.dhcp.umsl.edu/brats/index.php |title=BRaTS@Home homepage (capture of 25 March 2010) |publisher=University of Missouri-St. Louis |access-date=August 20, 2026 |archive-url=http://web.archive.org/web/20100325212718/http://maxwell.dhcp.umsl.edu:80/brats/index.php |archive-date=March 25, 2010 |url-status=dead}}</ref> Being tied to a campus network had its hazards, and the news archive chronicles a colorful series of interruptions: campus-wide power outages, a router and firewall failure that removed the whole campus from the Internet, an unannounced firewall change that forced a hiatus in early 2008 (used as an opportunity to upgrade to a newer BOINC server), and backbone upgrades by the campus Internet provider.<ref name=oldnews/><ref name=allnews/><ref name=home2009/>

In June 2008, Coss presented the project at the 212th meeting of the [[wikipedia:American Astronomical Society|American Astronomical Society]] in St. Louis, reporting that 182 users in 26 countries had joined, that 795 computers had connected to the server between June 2007 and April 2008, and that the volunteers supplied an average computing power of 1.1 billion [[wikipedia:FLOPS|floating point operations per second]] (GFLOPS). At the time, the BOINC platform as a whole averaged more than 1,000 [[wikipedia:FLOPS|teraFLOPS]], putting the scale of the small academic project in perspective.<ref name=aas/>

The project had an active community life for its size, with [[wikipedia:Internet forum|message boards]], participant profiles, a playful "BRaT of the day" profile feature, team competition (45 teams were registered over the project's life), certificates, and an RSS news feed.<ref name=home2009/><ref name=boincstats/> On January 23, 2010, Coss held an online discussion and question-and-answer session with volunteers about the project's results.<ref name=home2010/>

=== Completion (2010) ===

BRaTS@Home was, by design, a finite project: it existed to produce the simulations for Coss's dissertation. On March 24, 2010, he announced that he would defend his dissertation on April 9, 2010, and that the project would therefore come to an end. He thanked the volunteers, noting that the dissertation images combined data sets produced on multiple computers, so that "if you have been granted credit... it is likely your computer contributed to part of that."<ref name=wind-down/>

The scheduler was shut down on April 13, 2010, and volunteers were asked to detach from the project by mid-May 2010, when the university was expected to switch off the server.<ref name=shutdown>{{cite web |url=http://maxwell.dhcp.umsl.edu/brats/forum_thread.php?id=183 |title=Scheduler Shutdown (news thread, capture of 17 April 2010) |publisher=BRaTS@Home message boards |access-date=August 20, 2026 |archive-url=http://web.archive.org/web/20100417122439/http://maxwell.dhcp.umsl.edu:80/brats/forum_thread.php?id=183 |archive-date=April 17, 2010 |url-status=dead}}</ref> The final statistics export seen by BOINCstats is dated April 12, 2010, and records 79,464 total credits granted to 115 users and 492 host computers, with 45 teams.<ref name=boincstats/> Coss received his Ph.D. in physics in 2010,<ref name=cv>{{cite web |url=http://davecoss.com/cv.pdf |title=Curriculum Vitae of David Coss, Ph.D. |website=davecoss.com |access-date=August 20, 2026}}</ref> and mirrored the site's content at research.davecoss.com as a keepsake before the original server went dark.<ref name=wind-down/>

== Science ==

=== Gravitational lensing ===

[[File:Horseshoe_Einstein_Ring_from_Hubble.jpg|thumb|upright=1.25|right|Gravitational lensing in the real universe: the Hubble Space Telescope imaged a distant galaxy (blue) bent into a near-complete ring by the gravity of a foreground red galaxy.|alt=Hubble telescope image of a blue galaxy forming a horseshoe-shaped ring around a red galaxy]]

[[wikipedia:Gravitational lensing|Gravitational lensing]] is the deflection of light by gravity. A point mass <math>M</math> deflects a light ray passing at impact parameter <math>b</math> by the angle

:<math>\hat{\alpha} = \frac{4GM}{c^{2}b},</math>

where <math>G</math> is the gravitational constant and <math>c</math> the speed of light. In the thin-lens approximation, a mass distribution between a distant source and the observer maps the source position <math>\boldsymbol{\beta}</math> to the image position <math>\boldsymbol{\theta}</math> through the lens equation

:<math>\boldsymbol{\beta} = \boldsymbol{\theta} - \boldsymbol{\alpha}(\boldsymbol{\theta}), \qquad \boldsymbol{\alpha} = \frac{D_{ds}}{D_{s}}\, \hat{\boldsymbol{\alpha}},</math>

where <math>D_{ds}</math> and <math>D_s</math> are angular-diameter distances and <math>\boldsymbol{\alpha}</math> is the reduced deflection angle.<ref name=nasa2008/> Because the deflection depends only on the projected mass distribution, lensing offers a way to "see" [[wikipedia:Dark matter|dark matter]], which makes up most of the mass of galaxy clusters but emits no light.<ref name=nasa2009>{{cite conference |last1=Coss |first1=David |title=Gravitational Lensing Shear Simulations Using Fast Fourier Transform |conference=NASA Missouri Space Grant Consortium Annual Meeting |location=Missouri, USA |date=April 2009 |publisher=NASA Missouri Space Grant Consortium |url=http://research.davecoss.com/Coss_MOSGCpaper.pdf |access-date=August 20, 2026 |archive-url=https://web.archive.org/web/20200712022454/http://research.davecoss.com/Coss_MOSGCpaper.pdf |archive-date=July 12, 2020 |url-status=dead}}</ref>

In the weak-lensing regime the distortion is subtle: the shapes of background galaxies are stretched (shear) and magnified (convergence) by small amounts. Both are derived from the two-dimensional lensing potential <math>\psi</math>:

:<math>\kappa = \tfrac{1}{2}(\psi_{,11} + \psi_{,22}), \qquad
\gamma_{1} = \tfrac{1}{2}(\psi_{,11} - \psi_{,22}), \qquad
\gamma_{2} = \psi_{,12},</math>

which combine into the complex shear <math>\gamma = \gamma_{1} + i\,\gamma_{2}</math>. Measuring the statistical alignment of many background galaxies (cosmic shear) reveals the projected mass distribution of the foreground cluster.<ref name=nasa2009/>

=== The BRaTS approach ===

BRaTS@Home attacked the problem by brute-force [[wikipedia:Ray tracing|ray tracing]]: each work unit traced light rays through a model mass distribution, integrating the deflection they accumulate along the line of sight, and computing the resulting deflection angles on a grid.<ref name=aas/><ref name=thesis/> The project's main science application was named <code>ray_trace_ellipse</code>, and at its height it was issued for Windows 98 and later on x86 CPUs (version 3.00) and Linux on x86 CPUs (version 5.00), both installed on August 14, 2007; auxiliary applications named <code>test_app</code> and <code>deflector</code> were used for testing.<ref name=apps>{{cite web |url=http://maxwell.dhcp.umsl.edu/brats/apps.php |title=BRaTS@Home Applications (capture of 22 October 2007) |publisher=BRaTS@Home |access-date=August 20, 2026 |archive-url=http://web.archive.org/web/20071022170037/http://maxwell.dhcp.umsl.edu:80/brats/apps.php |archive-date=October 22, 2007 |url-status=dead}}</ref> The project's logo was itself a demonstration of the code: a ray-traced, gravitationally lensed image of the [[wikipedia:Andromeda Galaxy|Andromeda Galaxy]] (M31), based on an original astrophoto by Rob Gendler.<ref name=aboutimage>{{cite web |url=http://maxwell.dhcp.umsl.edu/brats/about_image.php |title=About the Image (capture of 23 July 2008) |publisher=BRaTS@Home |access-date=August 20, 2026 |archive-url=https://web.archive.org/web/20080723193054/http://maxwell.dhcp.umsl.edu/brats/about_image.php |archive-date=July 23, 2008 |url-status=dead}}</ref>

For his dissertation, Coss simulated gravitational lensing of realistic galaxy clusters using six high-resolution Adaptive Refinement Tree [[wikipedia:N-body simulation|N-body]] simulations of clusters (including hydrodynamics), plus a simulation of one group undergoing a merger. Each cluster's three-dimensional particle distribution was projected along three orthogonal lines of sight, yielding 21 projected mass density maps with representative masses and concentrations for the concordance cosmology.<ref name=thesis/>

Two simulation methods were compared. The first was the direct-integration ray tracing performed by BRaTS@Home's volunteers; the second computed shear maps with the [[wikipedia:Fast Fourier transform|fast Fourier transform]] (FFT), a technique also used in observational mass reconstructions. In Fourier space the convergence and shear are related by the Kaiser-Squires relation,

:<math>\hat{\gamma}(\boldsymbol{\ell}) = \hat{\kappa}(\boldsymbol{\ell})\, e^{2i\phi_{\ell}},</math>

where <math>\phi_\ell</math> is the polar angle of the Fourier mode <math>\boldsymbol{\ell}</math>; Coss's 2009 consortium paper examined the limitations and artifacts inherent in such FFT-based convolution calculations.<ref name=nasa2009/>

=== Results ===

[[File:Bullet cluster lensing.jpg|thumb|upright=1.25|left|Weak gravitational lensing maps the invisible: in the Bullet Cluster, lensing-derived mass (blue) is offset from the hot gas (red), evidence that most of the cluster's mass is dark matter. BRaTS@Home studied how cluster shape and substructure affect weak-lensing shear signals.|alt=Astronomical image of two colliding galaxy clusters with overlaid mass contours]]

The analysis showed that average shear measured inside and outside half the [[wikipedia:Virial radius|virial radius]] of the simulated clusters displays a distinct dispersion, varying by 24 percent from the mean across the 21 maps, while the estimated numerical error is of order 5 percent, meaning the dispersion is a reliable physical consequence of the clusters' shape differences. It correlates most strongly with the ratio of smallest-to-largest principal axis lengths of a cluster's isodensity shell. Image ellipticities, important for mass reconstruction, showed very little variance, but the tangential alignment of the average image distortion was strong enough that the locations of mass density peaks were easily resolvable.<ref name=thesis/> In short, the volunteers' computers helped establish how the shapes and substructure of dark matter halos imprint themselves on weak-lensing observables.

== Legacy ==

The project's ray-tracing and shear software was later packaged by Coss as ''CosApps'' (Cosmology Applications) and released as [[wikipedia:Free and open-source software|open source]] under the [[wikipedia:GPL-3.0|GNU General Public License v3]] on [[wikipedia:GitHub|GitHub]] in November 2012. The package provides <code>ray_trace_ellipse</code>, which can compute deflections in parallel across network-connected computers using [[wikipedia:MPI|MPI]], and <code>physcalc</code>, which calculates lensing shear from the coupled partial differential equations relating convergence and shear.<ref name=github>{{cite web |url=https://github.com/kd0kfo/cosmology |title=kd0kfo/cosmology |website=GitHub |access-date=August 20, 2026}}</ref> The code was registered with the [[wikipedia:Astrophysics Source Code Library|Astrophysics Source Code Library]] in December 2017 as ascl:1712.008.<ref name=ascl>{{cite web |url=http://ascl.net/1712.008 |title=CosApps: Simulate gravitational lensing through ray tracing and shear calculation |website=Astrophysics Source Code Library |date=December 2017 |bibcode=2017ascl.soft12008C |access-date=August 20, 2026}}</ref> Coss went on to a career in high-performance computing, including building a BOINC-based grid computing system at [[wikipedia:St. Jude Children's Research Hospital|St. Jude Children's Research Hospital]].<ref name=cv/>

The project is also a good early example of a BOINC project that ran to completion and delivered its promised science, wrapping up cleanly with a dissertation, a public results discussion, and a farewell archive for its participants.<ref name=wind-down/><ref name=shutdown/>

== Publications ==

=== Papers listed on the BOINC publications page ===

The BOINC project maintains a list of scientific publications arising from BOINC-based computing; the following entries are listed there for BRaTS@Home.<ref name=pubs>{{cite web |url=https://boinc.berkeley.edu/pubs.php |title=Publications by BOINC Projects |website=boinc.berkeley.edu |access-date=August 20, 2026}}</ref>

* {{cite thesis |last1=Coss |first1=David |title=Weak shear study of galaxy clusters by simulated gravitational lensing |type=Ph.D. thesis |institution=University of Missouri-St. Louis |date=2010 |bibcode=2010PhDT.......285C |url=https://ui.adsabs.harvard.edu/abs/2010PhDT.......285C/abstract |access-date=August 20, 2026}}
* {{cite conference |last1=Coss |first1=David Raymond |last2=Flores |first2=R. |title=BRaTS@Home and BOINC Distributed Computing for Parallel Computation |conference=212th Meeting of the American Astronomical Society, Poster 24.10 |location=St. Louis, Missouri |date=June 2-5, 2008 |bibcode=2008AAS...212.2410C |url=https://ui.adsabs.harvard.edu/abs/2008AAS...212.2410C/abstract |access-date=August 20, 2026}}

=== Other publications and presentations ===

Additional papers and presentations by the project author, hosted on the project's research site and documented in the author's curriculum vitae:<ref name=paperspage>{{cite web |url=http://research.davecoss.com/papers.html |title=Presentations of David Coss (capture of 12 July 2020) |website=research.davecoss.com |access-date=August 20, 2026 |archive-url=https://web.archive.org/web/20200712022414/http://research.davecoss.com/papers.html |archive-date=July 12, 2020 |url-status=dead}}</ref><ref name=cv/>

* {{cite conference |last1=Coss |first1=David |title=Simulation of Gravitational Lensing |conference=NASA Missouri Space Grant Consortium Annual Meeting (conference proceedings) |date=April 2008 |publisher=NASA Missouri Space Grant Consortium |url=http://research.davecoss.com/nasa_mo_paper.pdf |access-date=August 20, 2026 |archive-url=https://web.archive.org/web/20080827225312/http://research.davecoss.com/nasa_mo_paper.pdf |archive-date=August 27, 2008 |url-status=dead}}
* {{cite conference |last1=Coss |first1=David |title=Gravitational Lensing Shear Simulations Using Fast Fourier Transform |conference=NASA Missouri Space Grant Consortium Annual Meeting (conference proceedings) |date=April 2009 |publisher=NASA Missouri Space Grant Consortium |url=http://research.davecoss.com/Coss_MOSGCpaper.pdf |access-date=August 20, 2026 |archive-url=https://web.archive.org/web/20200712022454/http://research.davecoss.com/Coss_MOSGCpaper.pdf |archive-date=July 12, 2020 |url-status=dead}}
* {{cite conference |last1=Coss |first1=David |title=Effects of Dark Matter Halo Shape Variations on Weak Gravitational Lensing |conference=NASA Missouri Space Grant Consortium Annual Meeting (talk) |date=April 23-24, 2010 |publisher=NASA Missouri Space Grant Consortium}} (conference talk; results incorporated in the Ph.D. thesis)
* {{cite web |last1=Coss |first1=David |title=BRaTS@Home and BOINC Distributed Computing for Parallel Computation (poster abstract, author's copy) |website=research.davecoss.com |date=2008 |url=http://research.davecoss.com/AAS_abstract.pdf |access-date=August 20, 2026 |archive-url=https://web.archive.org/web/20200712022452/http://research.davecoss.com/AAS_abstract.pdf |archive-date=July 12, 2020 |url-status=dead}}
* {{cite web |last1=Coss |first1=David |title=CosApps: Simulate gravitational lensing through ray tracing and shear calculation (source code release) |website=Astrophysics Source Code Library |date=December 2017 |bibcode=2017ascl.soft12008C |url=http://ascl.net/1712.008 |access-date=August 20, 2026}}

== See also ==

* [[wikipedia:BOINC|BOINC]]
* [[BOINC projects]] (local project registry)
* [[wikipedia:Volunteer computing|Volunteer computing]]
* [[wikipedia:Gravitational lensing|Gravitational lensing]]
* [[wikipedia:Weak gravitational lensing|Weak gravitational lensing]]
* [[wikipedia:Dark matter|Dark matter]]
* [[Cosmology@Home]], a contemporary astrophysics BOINC project that also launched in June 2007
* [[Einstein@Home]]

==References==

{{Reflist}}

== External links ==

* {{URL|https://web.archive.org/web/20090322190553/http://maxwell.dhcp.umsl.edu/brats/|BRaTS@Home homepage (archived by the Wayback Machine)}}
* {{URL|https://www.boincstats.com/stats/48/project/detail|BRaTS@Home final statistics at BOINCstats}}
* {{URL|https://ui.adsabs.harvard.edu/abs/2010PhDT.......285C/abstract|Ph.D. thesis record at NASA ADS}}
* {{URL|https://github.com/kd0kfo/cosmology|CosApps source code (successor software) on GitHub}}
* {{URL|http://ascl.net/1712.008|CosApps record at the Astrophysics Source Code Library}}

[[Category:BOINC projects]]
[[Category:Completed BOINC projects]]
[[Category:Astronomy BOINC projects]]
[[Category:Volunteer computing]]
[[Category:Distributed computing]]
[[Category:Cosmology]]
[[Category:Dark matter]]

{{DEFAULTSORT:BRaTS@Home}}