Sfork issu 182

content/en/case-studies/gw-discov.md

@@ -3,49 +3,70 @@ title: "Case Study: Discovery of Gravitational Waves"
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-{{< figure src="/images/content_images/cs/gw_sxs_image.png" class="fig-center" caption="**Gravitational Waves**" alt="binary coalesce black hole generating gravitational waves" attr="(**Image Credits: The Simulating eXtreme Spacetimes (SXS) Project at LIGO** )" attrlink="https://youtu.be/Zt8Z_uzG71o" >}}
+{{< figure src="/images/content_images/cs/gw_sxs_image.png" 
+    class="fig-center" caption="**Gravitational Waves**" 
+    alt="binary coalesce black hole generating gravitational waves"
+    attr="(**Image Credits: The Simulating eXtreme Spacetimes (SXS) Project at LIGO** )"
+    attrlink="https://youtu.be/Zt8Z_uzG71o" >}}
 
 <blockquote cite="https://www.youtube.com/watch?v=BIvezCVcsYs">
-    <p>The scientific Python ecosystem is critical infrastructure for the research done at LIGO.</p>
-    <footer align="right">David Shoemaker, <cite>LIGO Scientific Collaboration</cite></footer>
+  <p>
+    The scientific Python ecosystem is critical infrastructure for the research
+    done at LIGO.
+  </p>
+  <footer align="right">
+    David Shoemaker,
+    <cite>LIGO Scientific Collaboration</cite>
+  </footer>
 </blockquote>
 
-## About [Gravitational Waves](https://www.nationalgeographic.com/news/2017/10/what-are-gravitational-waves-ligo-astronomy-science/) and [LIGO](https://www.ligo.caltech.edu)
-
-Gravitational waves are ripples in the fabric of space and time, generated by
-cataclysmic events in the universe such as collision and merging of two black
-holes or coalescing binary stars or supernovae. Observing GW can not only help
-in studying gravity but also in understanding some of the obscure phenomena in
-the distant universe and its impact.
-
-The [Laser Interferometer Gravitational-Wave Observatory (LIGO)](https://www.ligo.caltech.edu)
-was designed to open the field of gravitational-wave astrophysics through the
-direct detection of gravitational waves predicted by Einstein’s General Theory
-of Relativity. It comprises two widely-separated interferometers within the
-United States—one in Hanford, Washington and the other in Livingston,
-Louisiana—operated in unison to detect gravitational waves. Each of them has
-multi-kilometer-scale gravitational wave detectors that use laser
-interferometry.  The LIGO Scientific Collaboration (LSC), is a group of more
-than 1000 scientists from universities around the United States and in 14
-other countries supported by more than 90 universities and research institutes;
-approximately 250 students actively contributing to the collaboration. The new
-LIGO discovery is the first observation of gravitational waves themselves,
-made by measuring the tiny disturbances the waves make to space and time as
-they pass through the earth.  It has opened up new astrophysical frontiers
-that explore the warped side of the universe—objects and phenomena that are
-made from warped spacetime.
-
+## About Gravitational Waves and [LIGO](https://www.ligo.caltech.edu)
+
+[Gravitational
+waves](https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves)
+are ripples in the fabric of spacetime, generated by cataclysmic events in the
+universe such as collision and merging of two black holes, coalescing binary
+stars, supernovae or [compact
+binaries](https://wwwmpa.mpa-garching.mpg.de/~hsr/researchcb-en.html). Observing
+GW can not only help in studying gravity but also in understanding some of the
+obscure phenomena in the distant universe and its impact. Two of the most recent
+events in the context of gravitaional waves are the focus of this case study:
+
+* [GW observations from LIGO/Virgo
+GW150914](https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves):
+The original discovery of gravitational waves from a binary black hole merger
+* [GW observations from LiGO/Virgo
+GW170817](https://en.wikipedia.org/wiki/GW170817): The first direct detection
+of neutron start mergers 
+
+The [Laser Interferometer Gravitational-Wave Observatory
+(LIGO)](https://www.ligo.caltech.edu) was designed to open the field of
+gravitational-wave astrophysics through the direct detection of gravitational
+waves predicted by Einstein’s General Theory of Relativity. It comprises two
+widely-separated interferometers within the United States—one in Hanford,
+Washington and the other in Livingston, Louisiana—operated in unison to detect
+gravitational waves. Each of them has multi-kilometer-scale gravitational wave
+detectors that use laser interferometry.  The LIGO Scientific Collaboration
+(LSC), is a group of more than 1000 scientists from universities around the
+United States and in 14 other countries supported by more than 90 universities
+and research institutes; approximately 250 students actively contributing to the
+collaboration. LIGO discovery GW150914 is the first observation that is
+significant in being the first observation both confirming the existence of
+gravitational waves as well as proves the ability to directly measure them. 
+
+Gravitational waves allow scientists to observe and study the universe in a
+brand new way, ushering in the era of gravitational wave astronomy.
 
 ### Key Objectives
 
 * Though its [mission](https://www.ligo.caltech.edu/page/what-is-ligo) is to
   detect gravitational waves from some of the most violent and energetic
-  processes in the Universe, the data LIGO collects may have far-reaching
-  effects on many areas of physics including gravitation, relativity,
-  astrophysics, cosmology, particle physics, and nuclear physics.
+processes in the Universe, the data LIGO collects may have far-reaching effects
+on many areas of physics including gravitation, relativity, astrophysics,
+cosmology, particle physics, and nuclear physics.
 * Crunch observed data via numerical relativity computations that involves
   complex maths in order to discern signal from noise, filter out relevant
-  signal and statistically estimate significance of observed data 
+signal and statistically estimate significance of observed data 
 * Data visualization so that the binary / numerical results can be
   comprehended.
 
@@ -55,81 +76,93 @@ made from warped spacetime.
 * **Computation**
 
     Gravitational Waves are hard to detect as they produce a very small effect
-    and have tiny interaction with matter.  Processing and analyzing all of
-    LIGO's data requires a vast computing infrastructure.After taking care of
-    noise, which is billions of times of the signal, there is still very
-    complex relativity equations and huge amounts of data which present a
-    computational challenge:
-    [O(10^7) CPU hrs needed for binary merger analyses](https://youtu.be/7mcHknWWzNI)
-    spread on 6 dedicated LIGO clusters 
+and have tiny interaction with matter.  Processing and analyzing all of LIGO's
+data requires a vast computing infrastructure.After taking care of noise, which
+is billions of times of the signal, there is still very complex relativity
+equations and huge amounts of data which present a computational challenge:
+[O(10^7) CPU hrs needed for binary merger
+analyses](https://youtu.be/7mcHknWWzNI) spread on 6 dedicated LIGO clusters 
 
 * **Data Deluge**
 
     As observational devices become more sensitive and reliable, the challenges
-    posed by data deluge and finding a needle in a haystack rise multi-fold.
-    LIGO generates terabytes of data every day! Making sense of this data
-    requires an enormous effort for each and every detection. For example, the
-    signals being collected by LIGO must be matched by supercomputers against
-    hundreds of thousands of templates of possible gravitational-wave signatures.
+posed by data deluge and finding a needle in a haystack rise multi-fold.  LIGO
+generates terabytes of data every day! Making sense of this data requires an
+enormous effort for each and every detection. For example, the signals being
+collected by LIGO must be matched by supercomputers against hundreds of
+thousands of templates of possible gravitational-wave signatures. 
 
 * **Visualization**
 
-    Once the obstacles related to understanding Einstein’s equations well
-    enough to solve them using supercomputers are taken care of, the next big
-    challenge was making data comprehensible to the human brain. Simulation
-    modeling as well as  signal detection requires effective visualization
-    techniques.  Visualization also plays a role in lending more credibility
-    to numerical relativity in the eyes of pure science aficionados, who did
-    not give enough importance to numerical relativity until imaging and
-    simulations made it easier to comprehend results for a larger audience.
-    Speed of complex computations and rendering, re-rendering images and
-    simulations using latest experimental inputs and insights can be a time
-    consuming activity that challenges researchers in this domain.
-
-{{< figure src="/images/content_images/cs/gw_strain_amplitude.png" class="fig-center" alt="gravitational waves strain amplitude" caption="**Estimated gravitational-wave strain amplitude from GW150914**" attr="(**Graph Credits:** Observation of Gravitational Waves from a Binary Black Hole Merger, ResearchGate Publication)" attrlink="https://www.researchgate.net/publication/293886905_Observation_of_Gravitational_Waves_from_a_Binary_Black_Hole_Merger" >}}
+    Once the obstacles related to understanding Einstein’s equations well enough
+to solve them using supercomputers are taken care of, the next big challenge was
+making data comprehensible to the human brain. Simulation modeling as well as
+signal detection requires effective visualization techniques.  Visualization
+also plays a role in lending more credibility to numerical relativity in the
+eyes of pure science aficionados, who did not give enough importance to
+numerical relativity until imaging and simulations made it easier to comprehend
+results for a larger audience.  Speed of complex computations and rendering,
+re-rendering images and simulations using latest experimental inputs and
+insights can be a time consuming activity that challenges researchers in this
+domain.
+
+{{< figure src="/images/content_images/cs/gw_measurement.png" 
+    class="fig-center" alt="gravitational waves measurement" 
+    caption="**LIGO measurement of gravitational waves at Hanford and Livingston comparing signals to those expected due to a black hole merger event**" 
+    attr="(**Graph Credits:** LIGO Scientific Collboration & Virgo Collaboration" 
+    attrlink="https://physics.aps.org/featured-article-pdf/10.1103/PhysRevLett.116.061102" >}}
 
 ## NumPy’s Role in the detection of Gravitational Waves
 
 Gravitational waves emitted from the merger cannot be computed using any
-technique except brute force numerical relativity using supercomputers.
-The amount of data LIGO collects is as incomprehensibly large as gravitational
-wave signals are small.
-
-NumPy, the standard numerical analysis package for Python,  was utilized by
-the software used for various tasks performed during the GW detection project
-at LIGO. NumPy helped in solving complex maths and data manipulation at high
-speed.  Here are some examples:
-
-* [Signal Processing](https://www.uv.es/virgogroup/Denoising_ROF.html): Glitch
-  detection,  [Noise identification and Data Characterization](https://ep2016.europython.eu/media/conference/slides/pyhton-in-gravitational-waves-research-communities.pdf)
-  (NumPy, scikit-learn, scipy, matplotlib, pandas, pyCharm )
+technique except brute force numerical relativity using supercomputers.  The
+amount of data LIGO collects is as incomprehensibly large and requires careful
+processing like any other data science problem.  Although it is technologically
+more challenging to achieve the requisite sensitivity for capturing
+gravitaional waves and is way harder than dealing with large scale data, yet
+the latter is complex enough to require numerical processing skills of several
+Python tools including
+[NumPy](https://towardsdatascience.com/2020-how-a-i-could-help-astronomers-sorting-big-data-811571705707).
+
+NumPy, the standard numerical analysis package for Python,  was utilized by the
+software used for various tasks performed during the GW detection project at
+LIGO. NumPy helped in solving complex maths and data manipulation at high speed.
+Here are some examples:
+
+* **[Signal Processing](https://www.uv.es/virgogroup/Denoising_ROF.html):**  Glitch
+  detection,  [Noise identification and Data
+Characterization](https://ep2016.europython.eu/media/conference/slides/pyhton-in-gravitational-waves-research-communities.pdf)
+(NumPy, scikit-learn, scipy, matplotlib, pandas, pyCharm )
+* **GW data analysis:**
+  [GwPy](https://gwpy.github.io/docs/stable/overview.html) and
+[PyCBC](https://pycbc.org) are two of the [key LIGO experimentation 
+softwares](https://github.com/lscsoft) 
+that use NumPy and AstroPy under the hood, for providing
+object based interfaces to utilities, tools and methods for studying data from
+gravitational-wave detectors. Both GwPy and pycbc libraries rely on NumPy for
+analysis of the "chirp" signal. For example, in pycbc, the time series data are
+stored in ndarrays and scipy.signal, which operates on NumPy arrays.
 * Data retrieval: Deciding which data can be analyzed, figuring out whether it
   contains a signal - needle in a haystack
 * Statistical analysis: estimate the statistical significance of observational
   data, estimating the signal parameters (e.g. masses of stars, spin velocity,
-  and distance) by comparison with a model.
+and distance) by comparison with a model.
 * Visualization of data
   - Time series
   - Spectrograms
-* Compute Correlations 
-* Key [Software](https://github.com/lscsoft) developed in GW data analysis
-  such as [GwPy](https://gwpy.github.io/docs/stable/overview.html) and
-  [PyCBC](https://pycbc.org) uses NumPy and AstroPy under the hood for
-  providing object based interfaces to utilities, tools and methods for
-  studying data from gravitational-wave detectors.
 
 ## Summary
 
 GW detection has enabled researchers to discover entirely unexpected phenomena
 while providing new insight into many of the most profound astrophysical
-phenomena known. Number crunching and data visualization is a crucial step
-that helps scientists gain insights into data gathered from the scientific
-observations and understand the results. The computations are complex and
-cannot be comprehended by humans unless it is visualized using computer
-simulations that are fed with the real observed data and analysis.  NumPy
-along with other Python packages such as matplotlib, pandas and scikit-learn
-is [enabling researchers](https://www.gw-openscience.org/events/GW150914/) to
-answer complex questions and discover new horizons in our understanding of the
-universe.
-
-{{< figure src="/images/content_images/cs/numpy_gw_benefits.png" class="fig-center" alt="numpy benefits" caption="**Key NumPy Capabilities utilized**" >}}
+phenomena known. Number crunching and data visualization is a crucial step that
+helps scientists gain insights into data gathered from the scientific
+observations and understand the results. The computations are complex and cannot
+be comprehended by humans unless it is visualized using computer simulations
+that are fed with the real observed data and analysis.  NumPy along with other
+Python packages such as matplotlib, pandas and scikit-learn is [enabling
+researchers](https://www.gw-openscience.org/events/GW150914/) to answer complex
+questions and discover new horizons in our understanding of the universe.
+
+{{< figure src="/images/content_images/cs/numpy_gw_benefits.png"
+    class="fig-center" alt="numpy benefits" caption="**Key NumPy Capabilities utilized**" >}}