-November 26, 2012, a lecture at Sonoma State University by David Schlegel. The projects called BOSS and BigBOSS were presented which have the objective of creating a 3D map of the Universe. The map of galaxies would stretch from today’s Milky Way Galaxy to the Cosmic Microwave Background radiation 13 billion years back in time. Evidence tells us that galaxies first began to form 200 million years after the Big Bang.
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- BOSS stands for Baryonic Oscillations Space Survey. Baryonic oscillations are a fancy name for sound waves, density waves of oscillating atoms. In the early Universe it was so hot, > 3000 Kelvin, that electrons and protons existed in a plasma of free electrons and ions. The temperature was so high that the electromagnetic force could not hold the charged particles together. The electrons and protons could not combine to become neutral atoms of hydrogen or helium. The photons could not escape this charged plasma. The Universe was opaque.
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- After 380,000 years the plasma expanded and cooled to <3000 Kelvin and the neutral atoms began to form. Photons escaped and the Universe became transparent. The sound waves were frozen in the plasma at the instant this transition happened. Sound waves could travel through the plasma, but, they could not travel through free space full of neutral atoms. The opposite was happening with photons that were free in space to begin expanding with the expanding Universe. This first light was stretched in wavelength as it traveled through expanding space and today reaches us as the Cosmic Microwave Background Radiation. (CMB).
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- The CMB contains the structure of the sound waves that were frozen in time. The CMB is not perfectly smooth as we scan across the sky. Its structure at the fine detail level, 1 part in 100,000, contains the evidence of these sound waves. Sound waves are density waves with some regions higher density of mass and other regions lower density, void of mass. The higher density regions had the gravitational force needed to pull stars and galaxies together. The lower density regions became the voids between galaxies. Netlike tendrils interconnected the galaxy clusters. The sound wave imprint of 13 billion years ago has become the expanded galaxy structure we see today. Gravity was pulling things together and Dark Energy was expanding and pulling things apart.
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- The CMB sound waves varied in density by 1 part in 100,000 each wavelength 1 arc degree apart. After 13.7 billion years of expansion these wavelengths are 480.1 lightyears across. This is the average separation of galaxies that we see today.
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- During the first 7 billion years of the Universe expansion the force of gravity was the dominant force. At that point the Dark Energy force that was expanding the Universe became the dominant force overcoming gravity. For the last 7 billion years the Universe has been accelerating in its rate of expansion. We do not know the nature of this force. For lack of a better name we simply call it Dark Energy.
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- The BOSS project wanted to construct a 3D map that showed the evolution of this structure from the beginning to today. A telescope can map the images of galaxies in 2 dimensions, ( x and y ). To get the 3rd dimension the telescopes had to measure distance, (x, y and z). To accomplish this an aluminum plate was constructed at the focal plane of the telescope. Holes were drilled into the plate precisely at the location of each galaxy on the image. Fiber optic cables were installed in each hole in the plate. There were over 1,000 holes. The other end of the fiber cable 40 meters away was a spectrograph that could measure the redshift distance of each galaxy. With all the distances calculated a computer simulation could construct a 3D map of all the galaxies that were imaged.
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- Each 3D image of the sky could be completed in 15 minutes. Each time it was repeated a new aluminum plate with new holes had to be installed. It took over 1,000 plates to image the entire sky. The project measured distances for over 1,500,000 galaxies and 160,000 quasars. The result was computer modeled into a 3D video that you can watch. It is an amazing experience well worth your time to Google it. You can imagine flying in a spaceship through the galaxies, galaxy clusters, and voids, backwards in time to the original formation of galaxies. It is quite a journey.
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- BOSS uses a wide-angle lens that looks at 3 degrees of sky for each image. The Hubble Space Telescope could do this mapping but it would take 200,000 years. Because Hubble has such a narrow field of view it is like looking through an 8 foot soda straw. The SLOAN telescope with a 7 square degrees can view and image with 120 million pixels. It could map the entire sky in a single night.
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- BigBOSS is the next iteration of this same project. It just received a $2,100,000 grant in funding. BigBOSS is the latest in cosmological technology designed to measure Dark Energy to high precision. It hopes to also determine the mass of neutrinos and the number in the neutrino family.
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- It will use a bigger telescope 1.1 meter Mayall Telescope at the Kitt Peak observatory in Arizona. The Mayall Telescope currently has a half degree field of view. It will be modified to see 3 square degrees. Instead of installing individual fibers by hand this new telescope will install a 3 position fiber optic robots in each hole. Each fiber then can be positioned remotely using 10,000 tiny motors controlling each fiber’s position. A total of 5,000 optical cables will individually focus on 5,000 galaxies at one time. The fiber cables go back to 10 spectrographs each with dichroic beam splitters to select blue, red, and near infrared wavelengths in each light spectrum. A camera will record each spectrum and calculations of the redshifts will determine the distance to each galaxy. When BigBOSS sees first light next year it will create a 3D map of over 24,000,000 galaxies and 2,000,000 quasars covering the Northern Hemisphere and 13 billion lightyears of evolution.
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- I encourage you to see these 3D videos on YouTube. Google BOSS or David Schlegel of Lawrence Livermore Labs for videos and lectures about the project.
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- There is so much to learn. There is so much we do not know. What is the Dark Matter that interacts with gravity and comprises 23% of the Universe? What is Dark Energy that is the repelling force accelerating the expansion of the Universe and comprising 72% of the total mass-energy. The remaining 5% comprises the atoms and the other 3 forces that make up the Natural Universe we are a little bit more familiar with.
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- Dark Matter and Dark Energy are observational evidence of what we don’t know. the more we learn the more we know we don’t know. Science advances our knowledge in two fronts. We gain observational evidence of something that we have no theory to explain. Or, we imagine a theory that we have no observational evidence to confirm. This is often done with mathematics. It is the Ying and Yang of advancing science. Newton said: “ I feel like a child walking along the shore of knowledge picking up a shell here and a shell there with the being a whole ocean of the unknown in front of me.”
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- Maybe a student reading this review will be part of new discoveries to explain Dark Matter or Dark Energy. An announcement will be made shortly, stay tuned.
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