Constante de Hubble: uma nova maneira de medir a expansão do universo

quinta-feira, julho 28, 2011

Hubble Constant: A New Way to Measure the Expansion of the Universe

ScienceDaily (July 27, 2011) — Using a measurement of the clustering of the galaxies surveyed, plus other information derived from observations of the early universe, researchers have measured the Hubble constant with an uncertainly of less than 5 percent. The new work draws on data from a survey of more than 125,000 galaxies.

The 6df Galaxy Survey data, each dot is a galaxy and Earth is at the center of the sphere. (Credit: Image courtesy of International Centre for Radio Astronomy Research)

A PhD student from The International Centre for Radio Astronomy Research (ICRAR) in Perth has produced one of the most accurate measurements ever made of how fast the Universe is expanding.

Florian Beutler, a PhD candidate with ICRAR at the University of Western Australia, has calculated how fast the Universe is growing by measuring the Hubble constant.

"The Hubble constant is a key number in astronomy because it's used to calculate the size and age of the Universe," said Mr Beutler.

As the Universe swells, it carries other galaxies away from ours. The Hubble constant links how fast galaxies are moving with how far they are from us.

By analysing light coming from a distant galaxy, the speed and direction of that galaxy can be easily measured. Determining the galaxy's distance from Earth is much more difficult. Until now, this has been done by observing the brightness of individual objects within the galaxy and using what we know about the object to calculate how far away the galaxy must be.

This approach to measuring a galaxy's distance from Earth is based on some well-established assumptions but is prone to systematic errors, leading Mr Beutler to tackle the problem using a completely different method.

Published July 26 in the Monthly Notices of the Royal Astronomical Society, Mr Beutler's work draws on data from a survey of more than 125,000 galaxies carried out with the UK Schmidt Telescope in eastern Australia. Called the 6dF Galaxy Survey, this is the biggest survey to date of relatively nearby galaxies, covering almost half the sky.

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The 6dF Galaxy Survey: baryon acoustic oscillations and the local Hubble constant

Florian Beutler1,*, Chris Blake2, Matthew Colless3, D. Heath Jones4, Lister Staveley-Smith1, Lachlan Campbell5, Quentin Parker3,6, Will Saunders3, Fred Watson3

Article first published online: 25 JUL 2011

DOI: 10.1111/j.1365-2966.2011.19250.x

Monthly Notices of the Royal Astronomical Society © 2011 RAS

Keywords: surveys; cosmology: observations; dark energy; distance scale; large-scale structure of Universe


We analyse the large-scale correlation function of the 6dF Galaxy Survey (6dFGS) and detect a baryon acoustic oscillation (BAO) signal at 105 h−1 Mpc. The 6dFGS BAO detection allows us to constrain the distance–redshift relation at zeff= 0.106. We achieve a distance measure of DV(zeff) = 457 ± 27 Mpc and a measurement of the distance ratio, rs(zd)/DV(zeff) = 0.336 ± 0.015 (4.5 per cent precision), where rs(zd) is the sound horizon at the drag epoch zd. The low-effective redshift of 6dFGS makes it a competitive and independent alternative to Cepheids and low-z supernovae in constraining the Hubble constant. We find a Hubble constant of H0= 67 ± 3.2 km s−1 Mpc−1 (4.8 per cent precision) that depends only on the Wilkinson Microwave Anisotropy Probe-7 (WMAP-7) calibration of the sound horizon and on the galaxy clustering in 6dFGS. Compared to earlier BAO studies at higher redshift, our analysis is less dependent on other cosmological parameters. The sensitivity to H0 can be used to break the degeneracy between the dark energy equation of state parameter w and H0 in the cosmic microwave background data. We determine that w=−0.97 ± 0.13, using only WMAP-7 and BAO data from both 6dFGS and Percival et al. (2010).

We also discuss predictions for the large-scale correlation function of two future wide-angle surveys: the Wide field ASKAP L-band Legacy All-sky Blind surveY (WALLABY) blind H i survey (with the Australian Square Kilometre Array Pathfinder, ASKAP) and the proposed Transforming Astronomical Imaging surveys through Polychromatic Analysis of Nebulae (TAIPAN) all-southern-sky optical galaxy survey with the UK Schmidt Telescope. We find that both surveys are very likely to yield detections of the BAO peak, making WALLABY the first radio galaxy survey to do so. We also predict that TAIPAN has the potential to constrain the Hubble constant with 3 per cent precision.


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