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Category Archives: 18. Cosmology: the birth and life of the cosmos

From a press release of the Space Telescope Science Institute, January 26, 2017:

By using galaxies as giant gravitational lenses, an international group of astronomers using the Hubble Space Telescope have made an independent measurement of how fast the Universe is expanding. The newly measured expansion rate for the local Universe is consistent with earlier findings. These are, however, in intriguing disagreement with measurements of the early Universe. This hints at a fundamental problem at the very heart of our understanding of the cosmos.

The Hubble constant — the rate at which the Universe is expanding — is one of the fundamental quantities describing our Universe. A group of astronomers used the Hubble Space Telescope and other telescopes in space and on the ground to observe five galaxies in order to arrive at an independent measurement of the Hubble constant. This new measurement is completely independent of — but in excellent agreement with — other measurements of the Hubble constant in the local Universe that used Cepheid variable stars and supernovae as points of reference.

However, the value measured by this team, as well as those measured using Cepheids and supernovae, are different from the measurement made by the ESA Planck satellite. But there is an important distinction — Planck measured the Hubble constant for the early Universe by observing the cosmic microwave background.

Studied lensed quasars of H0LiCOW collaboration

Credit: ESA/Hubble, NASA, Suyu et al.

The targets of the new study were massive galaxies positioned between Earth and very distant quasars — incredibly luminous galaxy cores. The light from the more distant quasars is bent around the huge masses of the galaxies as a result of strong gravitational lensing. This creates multiple images of the background quasar, some smeared into extended arcs.

Because galaxies do not create perfectly spherical distortions in the fabric of space and the lensing galaxies and quasars are not perfectly aligned, the light from the different images of the background quasar follows paths which have slightly different lengths. Since the brightness of quasars changes over time, astronomers can see the different images flicker at different times, the delays between them depending on the lengths of the paths the light has taken. These delays are directly related to the value of the Hubble constant.

Links: the full STScI press release, including further figures and links to published papers.

From a UC Berkeley press release, June 2, 2016:

Astronomers have obtained the most precise measurement yet of how fast the universe is expanding at the present time, and it doesn’t agree with predictions based on other data and our current understanding of the physics of the cosmos. The discrepancy – the universe is now expanding 9 percent faster than expected – means either that measurements of the cosmic microwave background radiation are wrong, or that some unknown physical phenomenon is speeding up the expansion of space, the astronomers say.

“If you really believe our number – and we have shed blood, sweat and tears to get our measurement right and to accurately understand the uncertainties – then it leads to the conclusion that there is a problem with predictions based on measurements of the cosmic microwave background radiation, the leftover glow from the Big Bang,” said The Cosmos author Alex Filippenko, a co-author of a paper announcing the discovery. “Maybe the universe is tricking us, or our understanding of the universe isn’t complete.”

The cause could be the existence of another, unknown particle – perhaps an often-hypothesized fourth flavor of neutrino – or that the influence of dark energy (which accelerates the expansion of the universe) has increased over the 13.8 billion year history of the universe. Or perhaps Einstein’s general theory of relativity, the basis for the Standard Model, is slightly wrong.

“This surprising finding may be an important clue to understanding those mysterious parts of the universe that make up 95 percent of everything and don’t emit light, such as dark energy, dark matter and dark radiation,” said Nobel Laureate Adam Riess, the leader of the study. Riess is a former UC Berkeley post-doctoral fellow who worked with Filippenko. The results, using data from the Hubble Space Telescope and the Keck I telescope in Hawaii, will appear in an upcoming issue of The Astrophysical Journal.

Links: UC Berkeley press release with more details of the measurements; Hubble press release; the ApJ paper;

From a Berkeley Lab press release, April 30, 2015:

For the past several years, scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory have been planning the construction of and developing technologies for a very special instrument that will create the most extensive three-dimensional map of the universe to date. Called DESI for Dark Energy Spectroscopic Instrument, this project will trace the growth history of the Universe rather like the way you might track a child’s height with pencil marks climbing up a doorframe. But DESI will start from the present and work back into the past.

DESI will make a full 3D map pinpointing galaxies’ locations across the Universe. The map, unprecedented in its size and scope, will allow scientists to test theories of dark energy, the mysterious force that appears to cause the accelerating expansion and stretching of the Universe first discovered in observations of supernovae by groups led by Saul Perlmutter at Berkeley Lab and by Brian Schmidt, now at Australian National University, and Adam Riess, now at Johns Hopkins University.

Read interviews with Michael Levi and David Schlegel, two key physicists who have been involved in DESI from the beginning, here.

From ESA press releases, January 31 and February 5, 2015:

New maps from ESA’s Planck satellite uncover the ‘polarized’ light from the early Universe across the entire sky, revealing that the first stars formed much later than previously thought.

Planck_CMB

Credit: ESA and the Planck Collaboration

Between 2009 and 2013, Planck surveyed the sky to study this ancient light in unprecedented detail. Tiny differences in the background’s temperature trace regions of slightly different density in the early cosmos, representing the seeds of all future structure, the stars and galaxies of today.

Scientists from the Planck collaboration have recently published the results from the analysis of these data in a large number of scientific papers over the past two years, confirming the standard cosmological picture of our Universe with ever greater accuracy.

However, despite earlier reports of a possible detection of gravitational waves in the polarization of the CMB, a joint analysis of data from ESA’s Planck satellite and the ground-based BICEP2 and Keck Array experiments has found no conclusive evidence of primordial gravitational waves.

Links: full ESA press release and another one; Planck mission home; details about the CMB map including hi-res images.

Astronomers have discovered a distant quasar illuminating a vast nebula of diffuse gas, revealing for the first time part of the network of filaments thought to connect galaxies in a cosmic ‘web’. Researchers at the University of California, Santa Cruz, led the study, published January 19 in the journal, Nature. Using the 10-meter Keck I telescope in Hawaii, the researchers detected a very large, luminous nebula of gas extending about 2 million light-years across intergalactic space.

_72397147_72395239

Credit: S. Cantalupo (UCSC); Joel Primack (UCSC); Anatoly Klypin (NMSU)

The standard cosmological model of structure formation in the Universe predicts that galaxies are embedded in a cosmic web of matter, most of which (about 84 percent) is invisible dark matter. This web is seen in the results from computer simulations of the evolution of structure in the Universe, which show the distribution of dark matter on large scales, including the dark matter halos in which galaxies form and the cosmic web of filaments that connect them. Gravity causes ordinary matter to follow the distribution of dark matter, so filaments of diffuse, ionized gas are expected to trace a pattern similar to that seen in dark matter simulations.

Until now, these filaments have never been seen. Intergalactic gas has been detected by its absorption of light from bright background sources, but those results don’t reveal how the gas is distributed. In this study, the researchers detected the fluorescent glow of hydrogen gas resulting from its illumination by intense radiation from the quasar.

The hydrogen gas illuminated by the quasar emits ultraviolet light known as Lyman alpha radiation. The distance to the quasar is so great (about 10 billion light-years) that the emitted light is “stretched” by the expansion of the Universe from an invisible ultraviolet wavelength to a visible shade of violet by the time it reaches the Keck telescope and the spectrometer used for this discovery. Knowing the distance to the quasar, the researchers calculated the wavelength for Lyman alpha radiation from that distance and built a special filter to get an image at that wavelength.

Links: further images and information via the full Keck Observatory press release.

From the International Astronomical Union’s Newsletter of the Commission 46 on the Teaching of Astronomy (coauthor Pasachoff was president of the Commission):  An article in the American Journal of Physics, June 2013 (V81, pp. 414-420) describes a useful set of programs that illustrate techniques of analysis in modern cosmology, allowing students to “discover” the acceleration of the Universe. The authors are Jacob Moldenhauer, Larry Engelhardt, Keenan M. Stone, and Ezekiel Shuler from the Department of Physics and Astronomy, Francis Marion University, Florence, South Carolina, USA. Here is the abstract of the article: “We present a collection of new, open-source computational tools for numerically modeling recent large-scale observational data sets using modem cosmology theory. These tools allow both students and researchers to constrain the parameter values in competitive cosmological models, thereby discovering both the accelerated expansion of the universe and its composition (e.g., dark matter and dark energy). These programs have several features to help the non-cosmologist build an understanding of cosmological models and their relation to observational data, including a built-in collection of several real observational data sets. The current list of built-in observations includes several recent supernovae Type-Ia surveys, baryon acoustic oscillations, the cosmic microwave background radiation, gamma-ray bursts, and measurements of the Hubble parameter. In this article, we discuss specific results for testing cosmological models using these observational data.”

The software described in the article, called CosmoEJS, is freely available online from ComPADRE.