New books on Gravitational Lensing and Supernova Explosions; At 233rd AAS meeting J Silk and Alex Szalay talk about the future of cosmology and archived survey data

Greetings from Palmia Observatory


Well in the last post we had some discussion of gravitational lensing and supernova explosions so before going into some new presentations made at the 233rd AAS meeting, we offer some good reference texts and comments.
Recall that in our previous blog post describing one of the images from the Chandra x-ray observatory showed a view of the Bullet Cluster where two clumps of ordinary gas and two clumps of dark matter are identified.  Gravitational lensing was used to identify what the clump of dark matter was in order to explain the image.  Anyway, in order to more fully understand gravitational lensing, I picked up Scott Dodelson's latest 2017 book.

New textbook on gravitational lensing (Source: Scott Dodelson, "Gravitational Lensing)

I don't have any time right now to start reading this new book, but just opening up the first couple of pages there were these two images of observable gravitational lenses.  The first one is due to a mostly point source lens, like a single galaxy, that is just in a perfect line of sight between us and some distant galaxy.  The foreground galaxy, operating as a gravitational lens, bends the background light into a circular disk of light called an Einstein Ring.  Pretty neat!

The second image is not quite as easy to see in that it is an observed gravitational lens where the lens is not a single galaxy but a cluster of galaxies so that the background light from some more distant galaxy is bent into, not a perfect circle, but a series of arcs.  Measuring how much the light is bent, using general relativity calculations, then is an indication of how much matter, ordinary or dark, is present in the foreground lens.  Again, pretty neat!

Two examples of gravitational lensing; first for point objects and 2nd for a diffuse lens (Source: Scott Dodelson)

Also in the last post we mentioned how Chandra X-ray observations are used to track the evolution of supernova explosions.  Not knowing much about the details of the explosion, like for instance how does the iron core at the very center of the exploding star, get so quickly to the outer edges of the supernova remnant?  So, another great book available at the AAS meeting was this new 2017 edition of "Supernova Explosions."  Now I just have to get it on my reading stack!

Just opening up the book to the first couple of pages, we find this interesting compilation of spectra collected from the four main types of supernova explosions.  Remember that the Type 1a explosions are used as standard candles to measure the expansion of the universe and existence of dark energy, for example.  Again, pretty neat!

This 700 page, 2017 edition of Supernova Explosions looks very informative (Source: Branch and Wheeler)

Early time spectra of the four main types of supernova explosions  (Source: Branch and Wheeler)

Ok, now back to my last day at the 233rd AAS meeting in Seattle.  Joseph Silk, one of the premier cosmology experts, talked about the "future of cosmology."  Studying cosmology and trying to outline the history and evolution of the universe requires more and more data of higher resolution.  Higher resolution measurements allows for constraining the types of theories that are still consistent with the new data.

Joseph Silk in a plenary session lecture: The Future of Cosmology (Source: 233rd AAS meeting in Seattle)

With respect to cosmology the increasing resolution of CMB measurements starting primarily with COBE, then WMAP and finally Planck, many models of cosmology have been ruled out and new schemes have come about to explain the latest data.

What is next?  Joseph Silk explains that one approach to getting higher resolution data is to go to the far side of the moon, which is radio quiet enough, that these higher resolution measurements could be made with large arrays of radio dipoles.  In a statistical sense, is all boils down to the fact that the random error in your measurements goes down at a rate proportional to the square root of the number of measurements or modes of measurement in this case.  Knowing the value of some astronomical "constant" to say within 1% is not sufficient to rule out some of the theories, so getting down to 0.1% and 0.01% and below is required to make more progress.  Pretty neat, thanks for that Dr. Silk!

Joseph Silk explains need for higher resolution and measuring from the moon  (Source: 233rd AAS meeting in Seattle)

Alex Szalay gave a plenary session lecture on the era of surveys and the 5th paradigm of science.  His central point was that in this new era of big data astronomy we can collect data faster than it can be easily accessed or maintained for future studies.

Alex Szalay plenary session on "The era of surveys and the 5th Paradigm of Science (Source: 233rd AAS meeting)

One of his examples comes from the early archival of Sloan Digital Sky Survey (SDSS) data and how we can't just keep increasing the number of disk drives.  Modern scientists and even citizen scientists look for easy access tools for much of the archived data.  It's not enough just to be able to download a big data file.  Wheat analysts are after now is just doing all the analysis on the server side and just deliver the results that they are interested in to their desktop.

Failed hard drives for SDSS shows we can't just keep doing this way  (Source: Alex Szalay at 233rd AAS meeting)

He talked about the increasing trend of new publishing models where the access to journals is becoming freely available to all interested parties.  Yet, publishers used to have an incentive to publish and maintain journals, all of this model is now being questioned.  I know for me, just being finally an affiliate member of AAS, with access to journals, was a big thing.  We are all used to viewing and reviewing and downloading papers from the arXiV site, without actually needing to subscribe to the high cost official journals.

The FAIR model is increasing in popularity   (Source: Alex Szalay at 233rd AAS meeting)

It costs data to perform the survey and also costs money to maintain the survey data for future use.  It is not just stored away in some disk drive anymore but must be accessible and available for many different uses on many different types of programs.  But research grants typically don't get worried about what to do with the data once the survey has been completed.

The initial survey cost is a sunk cost but future research papers still make progress  (Source: Alex Szalay at 233rd AAS meeting)

So, who will store and maintain and how will it be stored and accessed?  Some argue that it should be the government, which means sometimes the same funding agencies that supported the research survey in the first place.  Others think that the journal publishers should store the data.  But accessible data is different than just stacks of journals.  Maybe the university library will be the ultimate repository and access point for the survey data?

Choose two options between: Open/Free, Accessible and Self-Sustaining  (Source: Alex Szalay at 233rd AAS meeting)

So, Alex summarizes the problem and recognizes that today we spend something like $8B to gather the data, but who will maintain the data for all of the future research.  It is becoming the major problem.  Who will solve this problem and will they have a financial interest to do so?  Thanks for that illuminating presentation, Alex Szalay!

Failed hard drives for SDSS shows we can't just keep doing this way  (Source: Alex Szalay at 233rd AAS meeting)

Ok, well we had time to summarize two of the final plenary sessions.  Unfortunately, I couldn't get to many of the more technical sessions and will have to wait for the next AAS meeting.  But now, its time to take the train to the airport and hop a plane back to Orange County.  Still cloudy weather, but at least a rainbow showed up.

Waiting for my plane to leave the 233rd AAS meeting in Seattle with positive sign of a rainbow (Source: Palmia Observatory)

Until next time,

Resident Astronomer George

If you are interested in things astronomical or in astrophysics and cosmology

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