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Cosmic Journeys: How Large is the Universe?



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Blobrana


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Podcast: The Size and Age of the Universe with Wendy Freedman

The Milky Way galaxy is one among 100 billion galaxies in the universe, all of which are constantly expanding. In this podcast from a recent talk at the Hayden Planetarium, Director of the Carnegie Observatories Wendy Freedman describes how astronomers measure the size and age of the universe.
Dr. Freedmans lecture was part of the 2011 Bampton Lectures in America and was recorded at the Museum on April 5, 2011.
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Expansion rate of the Universe
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Title: Constraining the expansion rate of the Universe using low-redshift ellipticals as cosmic chronometers
Authors: Michele Moresco, Raul Jimenez, Andrea Cimatti, Lucia Pozzetti

We present a new methodology to determine the expansion history of the Universe analysing the spectral properties of early type galaxies (ETG). We found that for these galaxies the 4000\AA break is a spectral feature that correlates with the relative ages of ETGs. In this paper we describe the method, explore its robustness using theoretical synthetic stellar population models, and apply it using a SDSS sample of ~14 000 ETGs. Our motivation to look for a new technique has been to minimise the dependence of the cosmic chronometer method on systematic errors. In particular, as a test of our method, we derive the value of the Hubble constant H_0 = 72.3 ±2.8 (68% confidence), which is not only fully compatible with the value derived from the Hubble key project, but also with a comparable error budget. Using the SDSS, we also derive, assuming w=constant, a value for the dark energy equation of state parameter w = -0.8 ±0.2. Given the fact that the SDSS ETG sample only reaches z ~ 0.3, this result shows the potential of the method. In future papers we will present results using the high-redshift universe, to yield a determination of H(z) up to z ~ 1.

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Blobrana


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Cosmos 250 times bigger than visible universe

Just how big is the universe is a question that has baffled cosmologists for decades. But now scientists have reasons to believe that it is at least 250 times bigger than the visible universe.
Researchers at Oxford University and Imperial College, London, focused on measuring the curvature of the universe.
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Universe's Expansion
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NIST Telescope Calibration May Help Explain Mystery of Universe's Expansion

Is the expansion of the universe accelerating for some unknown reason? This is one of the mysteries plaguing astrophysics, and somewhere in distant galaxies are yet-unseen supernovae that may hold the key. Now, thanks to a telescope calibrated by scientists from the National Institute of Standards and Technology (NIST), Harvard University and the University of Hawaii, astrophysicists can be more certain of one day obtaining an accurate answer.
The NIST scientists travelled to the summit of Haleakala volcano in Hawaii to fine-tune the operation of billions of light-collecting pixels in the Pan-STARRS telescope, which scans the heavens for Type IA supernovae. These dying stars always shine with the same luminosity as other Type IA supernovae, making them useful to observers as "standard candles" for judging distance in the universe. Any apparent shift in the supernova's spectrum gives a measure of how the universe has expanded (or contracted) as the light travelled from the supernova to Earth.
Because Type IA's are valuable as signposts, astrophysicists want to be sure that when they observe one of these faraway stellar cataclysms, they are getting a clear and accurate picture - particularly important given the current mystery over why the rate of expansion of the universe appears to be increasing. For that, they need a telescope that will return consistent information about supernovae regardless of which of the roughly 1,400,000,000 pixels of its collector spots it.
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Hubble Constant
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Less than 100 years ago scientists didn't know if the universe was coming or going, literally. It even fooled the great mind of Albert Einstein. He assumed the universe must be static. But to keep the universe from collapsing under gravity like a house of cards, Einstein hypothesized there was a repulsive force at work, called the cosmological constant, that counterbalanced gravity's tug. Along came Edwin Hubble in 1923 who found that galaxies were receding from us at a proportional rate, called the Hubble constant, which meant the universe was uniformly expanding, so there was no need to shore it up with any mysterious force from deep space. In measuring how this expansion was expected to slow down over time, 11 years ago, two studies, one led by Adam Riess of the Space Telescope Science Institute and the Johns Hopkins University and Brian Schmidt of Mount Stromlo Observatory, and the other by Saul Perlmutter of Lawrence Berkeley National Laboratory, independently discovered dark energy, which seems to behave like Einstein's cosmological constant.
To better characterise dark energy, Riess used Hubble Space Telescope's crisp view (combined with 2003 data from NASA's Wilkinson Microwave Anisotropy Probe, WMAP) to refine the value of the universe's expansion rate to a precision of three percent. That's a big step from 20 years ago when astronomers' estimates for the Hubble constant disagreed by a factor of two. This new value implies that dark energy really is a steady push on the universe as Einstein imagined, rather than something more effervescent (like the early inflationary universe) that changes markedly over time.

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Title: A Redetermination of the Hubble Constant with the Hubble Space Telescope from a Differential Distance Ladder
Authors: Adam G. Riess (JHU, STScI), Lucas Macri (Texas A&M), Stefano Casertano (STScI), Megan Sosey (STScI), Hubert Lampeitl (UPort), Henry C. Ferguson (STScI), Alexei V. Filippenko (UCB), Saurabh W. Jha (Rutgers), Weidong Li (UCB), Ryan Chornock (UCB), Devdeep Sarkar (UCI)

We report observations of 240 Cepheid variables obtained with the Near Infrared Camera (NICMOS) through the F160W filter on the Hubble Space Telescope (HST). The Cepheids are distributed across six recent hosts of Type Ia supernovae (SNe Ia) and the "maser galaxy" NGC 4258, allowing us to directly calibrate the peak luminosities of the SNe Ia from the precise, geometric distance measurements provided by the masers. New features of our measurement include the use of the same instrument for all Cepheid measurements across the distance ladder and homogeneity of the Cepheid periods and metallicities thus necessitating only a differential measurement of Cepheid fluxes and reducing the largest systematic uncertainties in the determination of the fiducial SN Ia luminosity. The NICMOS measurements reduce differential extinction in the host galaxies by a factor of 5 over past optical data. Combined with an expanded of 240 SNe Ia at z<0.1 which define their magnitude-redshift relation, we find H_0=74.2 ±3.6, a 4.8% uncertainty including both statistical and systematic errors. We show that the factor of 2.2 improvement in the precision of H_0 is a significant aid to the determination of the equation-of-state of dark energy, w = P/(rho c²). Combined with the WMAP 5-year measurement of Omega_M h², we find w= -1.12 ±0.12 independent of high-redshift SNe Ia or baryon acoustic oscillations (BAO). This result is also consistent with analyses based on the combination of high-z SNe Ia and BAO. The constraints on w(z) now with high-z SNe Ia and BAO are consistent with a cosmological constant and improved by a factor of 3 from the refinement in H_0 alone. We show future improvements in H_0 are likely and will further contribute to multi-technique studies of dark energy.

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Size of the Universe
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Measuring the Universe and the entirety of space, time and matter contained therein is a problem that has occupied great minds for generations. The current assessment of the diameter is 93 billion light years, but this may be out - by a few billion light-years.
Now an international team of scientists has set out to refine the measurement, using data acquired by Nasa's Kepler space telescope. While the prime purpose of the US mission is to establish whether planets orbiting other stars might be habitable, the subsidiary group are hoping it will help them with another of the world's great mysteries.
They want to get more information about a certain type of star, a Cepheid, which is used to measure the diameter of the Universe.

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An astronomer from Scotland will use a powerful new telescope to try to find out the true size of the universe.
Dr Alan Penny from the University of St Andrews believes data from Nasa's Kepler satellite, launched last month, will show that current estimates of the size of the universe are not accurate.

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Blobrana


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Hubble constant
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Astronomers have arrived at the most precise measurement ever of the Hubble constant, the key to the secrets of the universe
Hoping to understand why the universe seems to be coming apart at its seams, a young astronomer and his colleagues have embarked on one of the oldest quests in cosmology, to measure how fast the universe is growing, how big it is and how old it is. That information is encoded in the value of a number known as the Hubble constant that has led astronomers on a merry chase for three-quarters of a century.

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Blobrana


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Posts: 131433
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Hoping to understand why the universe seems to be coming apart at its seams, a young astronomer and his colleagues have embarked on one of the oldest quests in cosmology, to measure how fast the universe is growing, how big it is and how old it is.
That information is encoded in the value of an elusive number known as the Hubble constant that has led astronomers on a merry chase for three-quarters of a century.

It is the most fundamental number in cosmology - Adam Riess, 38, an astronomer at the Space Telescope Science Institute and Johns Hopkins University, and one of the discoverers 10 years ago that some kind of dark energy is speeding up the expansion of the universe.

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