1 / 22

Dark Energy and Cosmic Sound

Dark Energy and Cosmic Sound. Bob Nichol on behalf of the SDSS Collaboration Copy of presentation to be given by Daniel Eisenstein at AAS meeting in San Diego at 9am PST today. Bob Nichol - ICG, Portsmouth. Synopsis.

neil-stephenson
Download Presentation

Dark Energy and Cosmic Sound

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Dark Energy and Cosmic Sound • Bob Nichol on behalf of the SDSS Collaboration • Copy of presentation to be given by Daniel Eisenstein at AAS meeting in San Diego at 9am PST today Bob Nichol - ICG, Portsmouth

  2. Synopsis • evidence that gravity played the major role in the growth of galaxies: the “Smoking gun” • we have detected the “acoustic oscillations”, a sound wave created in the first minute of the Universe • use “oscillation” as a “cosmic yardstick” to measure distances more accurately than before. • the most precise measurement yet of the geometry of the Universe: it’s flat to 1%! Bob Nichol - ICG, Portsmouth

  3. How did galaxies form? • Local universe is full of galaxies: Where did they come from? How did they form they way they did? • Our theory predicts they form via gravity from tiny quantum fluctuations in the early Universe Bob Nichol - ICG, Portsmouth

  4. Sound Waves in Early Universe Recombination z ~ 1000 ~400,000 years • For 400,000 years after the Big Bang, the cosmic microwave background photons are trapped in the ionized cosmic gas. • These photons provide an enormous restoring pressure, causing the gas to resist being squeezed by gravity • Therefore, fluctuations in the gas propagate as sound waves. • This ends abruptly when the Universe cools below 3000K and the gas becomes neutral: Universe suddenly becomes transparent Neutral Ionized Big Bang Today Time Bob Nichol - ICG, Portsmouth

  5. Cosmic Microwave Background • Effect of this sound wave already discovered in relic light of the early universe i.e. the CMB! • That was the Universe at 400,000 years. Can we see these sound waves today? Bob Nichol - ICG, Portsmouth

  6. Theory of the sound wave • At first, sound wave expands at 57% of the speed of light, then slows as the gas changes from ionized to neutral (red = ionized, green = neutral) • Final size is reached after one million years. Today, that radius is 500 million light years. • Central peak is overdense in dark matter. Outer ring is overdense in gas. Both are seeds for the formation of galaxies. Our theory accurately predicts an excess of galaxy pairs separated by 500 million light-years: this would be the “SMOKING GUN” that only gravity was important to explain the rich structures of galaxies and clusters of galaxies we see today Bob Nichol - ICG, Portsmouth

  7. The Sloan Digital Sky Survey • The Sloan Digital Sky Survey is a survey of (one quarter) of the northern sky. Over 200 scientists from 14 institutions around the world. • Here we report on a sample that covers 10% of the sky. • Luminous red galaxy sample: special spectroscopic sample of 47,000 galaxies that extends to z = 0.47, 6 billion light years away. Largest volume ever surveyed with galaxies (This is why we can see this wave) SDSS Telescope in Apache Point, New Mexico Bob Nichol - ICG, Portsmouth

  8. 500 Million Light Years A slice of the SDSS Credit: SDSS 700,000 light years Bob Nichol - ICG, Portsmouth

  9. The Correlation Function • The correlation function is the probability of finding pairs at a given separation, above that of a random distribution. Excess of galaxies separated by 500 million light years Bob Nichol - ICG, Portsmouth

  10. What does it mean? • We have detectedthe sound wave in the Universe at two very different epochs (400,000 yrs after Big Bang and present-day). This is important because our theory of gravitational structure formation predicts that such features should have been preserved. Detecting the sound wave in the galaxies is the “SMOKING GUN” that our theory is correct. • Better yet, the sound wave is an object of fixed size, a “standard ruler” or “cosmic yardstick”. This means that we can measure its apparent size anywhere in the Universe, and determine how far it is away because we know its true size. Bob Nichol - ICG, Portsmouth

  11. Looking back in time in the Universe Looking back in time in the Universe CMB SDSS GALAXIES FLAT GEOMETRY FLAT GEOMETRY CREDIT: WMAP & SDSS websites

  12. Looking back in time in the Universe Looking back in time in the Universe CMB SDSS GALAXIES FLAT GEOMETRY OPEN GEOMETRY CREDIT: WMAP & SDSS websites

  13. Looking back in time in the Universe Looking back in time in the Universe CMB SDSS GALAXIES FLAT GEOMETRY CLOSED GEOMETRY CREDIT: WMAP & SDSS websites

  14. UNIVERSE IS FLAT TO 1% PRECISION Bob Nichol - ICG, Portsmouth

  15. Dark Energy • In 1998, two groups used distant supernovae to discover the acceleration of the expansion history of the Universe. • supernovae were fainter than expected, implying that they were further away. • The cause of this is completely unknown but almost surely exotic new physics. It has been dubbed “dark energy”. Our detection requires dark energy to be correct! • Now we can map the expansion of the Universe using our “cosmic yardstick”. This is a robust and innovative new method for cosmologists and will spawn future surveys of the Universe. Bob Nichol - ICG, Portsmouth

  16. More Information • http://cmb.as.arizona.edu/~eisenste/acousticpeak • http://www.dsg.port.ac.uk/~nicholb/wiggles • bob.nichol@port.ac.uk Bob Nichol - ICG, Portsmouth

  17. Thanks to.... • The science analysis team was supported by several grants from the National Science Foundation, as well as funds from the University of Arizona, the Sloan Foundation, and NASA. • The SDSS is supported by the Alfred P. Sloan Foundation, NASA, the National Science Foundation, Dept of Energy, the Japanese Monbukagakusho, the Max Planck Society, and the Participating Institutions: University of Chicago, Fermilab, the Institute for Advanced Study, the Japanese Participation Group, the Johns Hopkins University, the Korean Scientist Group, the Max Planck Institute for Astronomy, the Max Planck Institute for Astrophysics, New Mexico State University, the University of Pittsburgh, the University of Portsmouth, Princeton University, the US Naval Observatory, and the University of Washington. Bob Nichol - ICG, Portsmouth

  18. EXTRA SLIDES • EXTRA SLIDES FOR Q&A Bob Nichol - ICG, Portsmouth

  19. What is going on (part 2) ? • Gravity squeezes the gas, pressure pushes back! They oscillate • When the Universe cools below 3000K these sound waves are frozen in Courtesy of Wayne Hu Bob Nichol - ICG, Portsmouth

  20. Cosmic Yardstick? If we know the true size of something, we can estimate how far it is away by it’s apparent size Satellite photos of Earth via Google can now be used to measure distances Bob Nichol - ICG, Portsmouth

  21. Color SDSS Data (Hogg & Blanton) LRG

  22. Life is more complicated • Universe is composed of many perturbations, all superimposed. • We do not expect to see bulls-eyes in the galaxy map. Indeed, the ring is only 1% of the height of the center. • The whole analysis is statistical. Therefore need massive datasets like SDSS Bob Nichol - ICG, Portsmouth

More Related