# Into the Cosmic Web

by on February 23, 2008

The more we learn about gravitational lensing, the more it becomes clear how pervasive the phenomenon must be as mass and spacetime interact throughout the cosmos. The most recent findings produced by lensing effects now limn structures so large that they dwarf the galaxy we reside in. Recently detected dark matter filaments, up to 270 million light years in size, are 2000 times the size of the Milky Way, yet would remain unobserved were it not for advanced lensing investigative techniques.

The astronomers behind this work, using data from the Canada-France-Hawaii Telescope Legacy Survey, took advantage of the fact that dark matter should deflect the light from distant galaxies as it travels towards us. The careful measurement of these often tiny effects required the development of new tools for image analysis, but these apparent filaments, sheets and clusters of dark matter seem to gibe with previous theoretical estimates. “Our observations extend the knowledge about the cosmic web far beyond what was known before,” says Liping Fu (Institut d’Astrophysique de Paris). “We confirmed that our model about the Universe is correct even on those very large scales.”

The model Fu is talking about is a paradigm of dark matter that sees galactic clusters and galaxies themselves embedded in the filamentary structures described above. The detection of such structures supports the evolving paradigm; had the filaments not been found, dark matter would be due for a profound re-thinking. Up until now, the observation of gravitational lensing at these weak levels had proven impossible.

Up next: Whole-sky surveys to further study dark matter distribution, probing whether its signature (and that of dark energy) can be explained by modifications to General Relativity. If not, then we do seem to be dealing with a new type of matter and source of energy. Either way, the advance in knowledge will be extraordinary. The paper is Fu, Semboloni et al., “Very weak lensing in the CFHTLS wide: cosmology from cosmic shear in the linear regime,” accepted by Astronomy & Astrophysics and available online.

James M. Essig February 23, 2008 at 19:51

Hi Folks;

Perhaps we will discover a new form of mass where M is not equal to M(C EXP2). such as: M = A x f(M[C EXP 2]); M = f(M [C EXP 2]) + f(b); M = f(M [C EXP 2]) + C; M = f(g)f(M[C EXP 2]); where A is a non-unity constant multiplier, f’s denote functions and C is an additive constant; and the list of candidates could go on and on. Moveover f’s could be exponential functions, logarithmic functions, trigonometric functions, complex functions, compound functions, product functions or summations of functions and/or combinations theorof etc. However, noting the simplicity of the general relativistic mass energy equivalence formula, any new form of mass or energy is likely to be fairly simple, especially for mattergy types most resembling general relativistic mattergy.

Perhaps Cold Dark Matter can and has formed cosmic strings, stupendously large blackholes perhaps with masses greater than Mbh = or > 10 EXP 15 solar masses and other exotic objects.

These large, apparently CDM structures, are really cool being that they can be at least 270 light years long. Will we find even larger structures thus perhaps requiring modification to Big Bang evolution concepts involving homogeneity.

Either way, learning about cold dark matter may help us find alternate ambient energy sources within the cosmos which might be collected, concentrated, or otherwise harvested for manned interstellar and intergalactic transport.

Hopefully, CERN’s LHC can shed some experimental light on the nature of Cold Dark Matter.

Thanks;

Jim

Bernd Missal February 24, 2008 at 10:22

Hi,

I don’t really understand the method used in this research.
The way I understand it they use statitics to measure the cosmic shear of background galaxies. But if the data are statistically derived there is no real measurement of individual galaxies.
Besides on what assumptions is all this based? It all seems a bit far fetched.
Anyway, I don’t really understand it. A thorough explanation would be nice.

Administrator February 24, 2008 at 13:46

As I understand it, Bernd, what can be observed is an extremely subtle elongation in the galaxies being observed that is consistent with weak gravitational lensing — i.e., it’s a coherent effect across the large segments of the field being measured. Improvements on the CFHT MegaPrime/MegaCam combination have made the new measurements possible. For more on the instrumentation, check http://www.cfht.hawaii.edu/News/CFHTLS0802/.

From earlier work (in 2000) using the precursor of the current instrumentation, here’s a description that also applies here: “The light from a distant galaxy rarely encounters a clump of mass to strongly bend the light and cause an easily seen distortion. Instead the individual light rays suffer a series of small deflections such that an observer… sees that the images of all the galaxies in some small patch of the sky, near to one of our test galaxies say, are all very slightly elongated in a common direction determined by the distribution of dark matter along that particular line of sight. This gravitational distortion is expected to be very small and requires a careful statistical treatment on many patches over the sky but has now been measured by the French team.”

More on that at http://www.cfht.hawaii.edu/News/Lensing/#FD.

Bernd Missal February 26, 2008 at 10:49

ljk February 27, 2008 at 14:46

WMAP Haze: Directly Observing Dark Matter?

Authors: Michael McNeil Forbes, Ariel R. Zhitnitsky

(Submitted on 26 Feb 2008)

Abstract: In this paper we show that dark matter in the form of dense matter/antimatter nuggets could provide a natural and unified explanation for several distinct bands of diffuse radiation from the core of the galaxy spanning over 13 orders of magnitude in frequency. We fix all of the phenomenological properties of this model by matching to X-ray observations in the keV band, and then calculate the unambiguously predicted thermal emission in the microwave band, at frequencies smaller by 11 orders of magnitude.

Remarkably, the intensity and spectrum of the emitted thermal radiation are consistent with – and could entirely explain – the so-called “WMAP haze”: a diffuse microwave excess observed from the core of our galaxy. This provides another strong constraint of our proposal, and a remarkable non-trivial validation. If correct, our proposal identifies the nature of the dark matter, explains baryogenesis, and provides a means to directly probe the matter distribution in our Galaxy by analyzing several different types of diffuse emissions.

Subjects: Astrophysics (astro-ph)

Report number: NT@UW-08-05

Cite as: arXiv:0802.3830v1 [astro-ph]

Submission history

From: Michael McNeil Forbes [view email]

[v1] Tue, 26 Feb 2008 16:15:27 GMT (41kb)

http://arxiv.org/abs/0802.3830

ljk February 28, 2008 at 6:36

U. S. Experiment Takes the Lead in the Competitive Race to Find Dark Matter

PASADENA, Calif.– Scientists of the Cryogenic Dark Matter Search
(CDMS) experiment, including researchers from the California
Institute of Technology, today announced that they have regained the
lead in the worldwide race by a number of different research groups
to find the particles that make up dark matter. The CDMS experiment,
which is being conducted a half-mile underground in a mine in Soudan,
Minnesota, again sets the world’s best constraints on the properties
of dark matter candidates.

Weakly interacting massive particles, or WIMPs, are leading
candidates for the building blocks of dark matter, the as-yet-unknown
form of matter that accounts for 85 percent of the entire mass of the
universe. Hundreds of billions of WIMPs may have passed through your
body as you read these sentences.

The CDMS experiment is located in the Soudan Underground Laboratory,
shielded from cosmic rays and other particles that could mimic the
signals expected from dark matter particles. Scientists operate the
ultrasensitive CDMS detectors under clean-room conditions at a
temperature of about 40 millikelvins, or .04 degrees Celsius above
absolute zero. Physicists believe that WIMPs, if they exist, would
travel right through ordinary matter, rarely leaving a trace. If
WIMPs were to cross the CDMS detector, occasionally one would hit the
nucleus of an atom of the element germanium in the crystal grid of
the detector. Like a hammer hitting a bell, the collision would
create vibrations of the grid, which scientists would be able to
detect. The experiment is sensitive enough to hear WIMPs if they hit
the crystal germanium detector only twice per year.

The scientists did not observe such signals, allowing the CDMS
experiment to set limits on the properties of WIMPs.

Scientists predict that WIMPs might interact with ordinary matter at
rates similar to those of low-energy neutrinos, elusive subatomic
particles discovered in 1956. But to account for all of the dark
matter in the universe and the gravitational pull it produces, WIMPs
must have masses about a billion times larger than those of
neutrinos. The CDMS collaboration found that if WIMPs have 100 times
the mass of protons (about 100 GeV/c^2) they collide with one
kilogram of germanium less than a few times per year; otherwise, the
CDMS experiment would have detected them.

“With our new result we are leapfrogging the competition,” says CDMS
cospokesperson Blas Cabrera, of Stanford University. The Department
of Energy’s Fermi National Accelerator Laboratory hosts the project
management for the CDMS experiment. “We have achieved the world’s
most stringent limits on how often dark matter particles interact
with ordinary matter and how heavy they are, in particular in the
theoretically favored mass range of more than 40 times the proton
mass.”

“The CDMS experiment is unique in bringing so many different
disciplines to bear on the search for dark matter, from astro- and
particle physics in the expected WIMP signature to low-temperature
and condensed-matter physics in the operation of our novel
detectors,” says Sunil Golwala, assistant professor of physics at
Caltech. “Our work continues Caltech’s long-standing role in the dark
matter story, ranging from the first evidence for dark matter
obtained by Fritz Zwicky in 1933 to the detailed maps of dark matter
made recently by Caltech astronomy colleagues Nick Scoville, Richard
Ellis, and Richard Massey.”

“Observations made with telescopes have repeatedly shown that dark
matter exists. It is the stuff that holds together all cosmic
structures, including our own Milky Way. The observation of WIMPs
would finally reveal the underlying nature of this dark matter, which
plays such a crucial role in the formation of galaxies and the
evolution of our universe,” says Joseph Dehmer, director of the
Division of Physics for the National Science Foundation.

The discovery of WIMPs would require extensions to the theoretical
framework known as the standard model of particles and their forces.
The CDMS result, presented to the scientific community at the Eighth
UCLA Dark Matter and Dark Energy symposium on February 22, tests the
viability of new theoretical concepts that have been proposed.

“Our results constrain theoretical models such as supersymmetry and
models based on extra dimensions of space-time, which predict the
existence of WIMPs,” says CDMS project manager Dan Bauer, of DOE’s
Fermilab. “For WIMP masses expected from these theories, we are again
the most sensitive in the world, retaking the lead from the Xenon 10
experiment at the Italian Gran Sasso laboratory. We will gain another
factor of three in sensitivity by continuing to take more data with
our detector in the Soudan laboratory until the end of 2008.”

A new phase of the CDMS experiment with 25 kilograms of germanium is
planned for the Sudbury Neutrino Observatory’s underground laboratory

“The 25-kilogram experiment has clear discovery potential,” says
Fermilab director Pier Oddone. “It covers a lot of the territory
predicted by supersymmetric theories.”

The CDMS collaboration includes more than 50 scientists from 15
institutions and receives funding from the U.S. Department of Energy,
the National Science Foundation, foreign funding agencies in Canada
and Switzerland, and member institutions.

In addition to participating in CDMS, Golwala’s dark matter group at
Caltech, comprising physics graduate students Zeeshan Ahmed and David
Moore and postdoctoral fellow in experimental physics Walt Ogburn, is
developing a new kind of WIMP detector based on the microwave kinetic
inductance sensors developed by Professor of Physics Jonas
Zmuidzinas, with funding from a grant by the Gordon and Betty Moore
Foundation.

http://cdms.berkeley.edu/index.html

Fermilab CMMS press page

http://www.fnal.gov/pub/presspass/press_releases/CDMS_Photos2008/index.html

ljk February 28, 2008 at 7:09

Spiral and Bar Instabilities Provoked by Dark Matter Satellites

Authors: John Dubinski, Jean-Rene Gauthier, Larry Widrow, Sarah Nickerson

(Submitted on 27 Feb 2008)

Abstract: We explore the secular dynamical evolution of an N-body model of M31 in the presence of a population of 100 dark matter satellites over 10 Gyr. The satellite population has structural and kinematic characteristics modelled to follow the predictions of Lambda-CDM cosmological simulations. Vertical disk heating is a small effect despite many interactions with the satellite population with only a 20% increase in vertical velocity dispersion sigma_z and the disk scale height z_d at the equivalent solar radius R = 2.5R_d . However, the stellar disk is noticeably flared after 10 Gyr with z_d nearly doubling at the disk edge. Azimuthal disk heating is much larger with sigma_R and sigma_z both increasing by 1.7x. However, in a control experiment without satellites dispersion increases by 1.5x suggesting that most of the effect is due to heating through scattering off of spiral structure excited by swing-amplified noise.

Surprisingly, direct impacts of satellites on the disk can excite spiral structure with a significant amplitude and in some cases impacts close to the disk center also induce the bar instability. The large number of dark matter satellite impacts expected over a galaxy’s lifetime may be a significant source of external perturbations for driving disk secular evolution.

Comments: 4 pages, 1 figure, 4 movies at this http URL, to appear in the proceedings of the ASP, Formation and Evolution of Galaxy Disks – Rome, Pontifical Gregorian University, 1-5 October 2007, ed. J.G Funes and E.M Corsini

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0802.3997v1 [astro-ph]

Submission history

From: John Dubinski [view email]

[v1] Wed, 27 Feb 2008 12:09:17 GMT (45kb)

http://arxiv.org/abs/0802.3997

ljk March 4, 2008 at 10:08

Numerical Simulations Unravel the Cosmic Web

Authors: C.-A. Faucher-Giguere, A. Lidz, L. Hernquist (Harvard University)

(Submitted on 3 Mar 2008)

Abstract: The universe is permeated by a network of filaments, sheets, and knots collectively forming a “cosmic web.” The discovery of the cosmic web, especially through its signature of absorption of light from distant sources by neutral hydrogen in the intergalactic medium, exemplifies the interplay between theory and experiment that drives science, and is one of the great examples in which numerical simulations have played a key and decisive role. We recount the milestones in our understanding of cosmic structure, summarize its impact on astronomy, cosmology, and physics, and look ahead by outlining the challenges faced as we prepare to probe the cosmic web at new wavelengths.

Comments: 10 pages, 2 figures. Appeared as a solicited Perspective article in the January 4, 2008 special issue of Science on the cosmic web

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0803.0147v1 [astro-ph]

Submission history

From: Claude-Andre Faucher-Giguere [view email]

[v1] Mon, 3 Mar 2008 02:15:04 GMT (394kb,D)

http://arxiv.org/abs/0803.0147

ljk March 6, 2008 at 10:27

Is dark matter made of axions?

From Physorg.com,

Feb. 26, 2008

One of the mysteries of our universe is that of dark energy and matter. Scientists all over the world are attempting to discover what particles make up dark energy and matter. “Axions are one of the particles considered for dark matter,” William Wester tells PhysOrg.com. “We were hoping to get a signal proving that they exist with this experiment.”

Wester, a scientist at the Fermi National Accelerator Laboratory in Batavia, Illinois, worked closely with Aaron Chou, now at New York University, and a group of scientists from Fermilab and the University of Michigan in Ann Arbor, to design an experiment to test the existence of axion-like particles within a certain range. Their results can be found in Physical Review Letters: “Search for Axionlike Particles Using a Variable-Baseline Photon-Regeneration Technique.”

http://www.physorg.com/news123770210.html

ljk March 10, 2008 at 11:11

Greedy Supermassive Black Holes Dislike Dark Matter

Written by Ian O’Neill

It is widely accepted that supermassive black holes (SMBHs) sit in the centre of elliptical galaxies or bulges of spiral galaxies. They suck in as much matter as possible, generating blasts of radiation. Stars, gas and everything else nearby forms a compact “halo” and then falls to a gravitationally enforced death spiral. The greedy nature and the sheer size of these black holes have led to the idea that dark matter may supply (or may have supplied) the SMBH with some mass during its evolution.

But could it be that dark matter may not be significantly involved after all? This might be one cosmic phenomenon dark matter can’t be blamed for…

http://www.universetoday.com/2008/03/08/greedy-supermassive-black-holes-dislike-dark-matter/

ljk April 2, 2008 at 6:37

The WIMPless Miracle

Authors: Jonathan L. Feng, Jason Kumar

(Submitted on 30 Mar 2008)

Abstract: We propose that dark matter is composed of particles that naturally have the correct thermal relic density, but have neither weak-scale masses nor weak interactions. These WIMPless models emerge naturally from gauge-mediated supersymmetry breaking, where they elegantly solve the dark matter problem. The framework accommodates single or multiple component dark matter, dark matter masses from 10 MeV to 10 TeV, and interaction strengths from gravitational to strong. These candidates enhance many direct and indirect signals relative to WIMPs and have qualitatively new implications for dark matter searches and cosmological implications for colliders.

Subjects: High Energy Physics – Phenomenology (hep-ph); Astrophysics (astro-ph); High Energy Physics – Experiment (hep-ex); High Energy Physics – Theory (hep-th)

Report number: UCI-TR-2008-10

Cite as: arXiv:0803.4196v1 [hep-ph]

Submission history

From: Jonathan Feng [view email]

[v1] Sun, 30 Mar 2008 05:03:04 GMT (71kb)

http://arxiv.org/abs/0803.4196

ljk April 2, 2008 at 6:39

Model-Independent Determination of the WIMP Mass from Direct Dark Matter Detection Data

Authors: Manuel Drees, Chung-Lin Shan

(Submitted on 31 Mar 2008)

Abstract: Weakly Interacting Massive Particles (WIMPs) are one of the leading candidates for Dark Matter. We develop a model–independent method for determining the mass $m_\chi$ of the WIMP by using data (i.e., measured recoil energies) of direct detection experiments. Our method is independent of the as yet unknown WIMP density near the Earth, of the form of the WIMP velocity distribution, as well as of the WIMP–nucleus cross section. However, it requires positive signals from at least two detectors with different target nuclei. In a background–free environment, $m_\chi \sim 50$ GeV could in principle be determined with an error of $\sim 35%$ with only $2 \times 50$ events; in practice upper and lower limits on the recoil energy of signal events, imposed to reduce backgrounds, can increase the error. The method also loses precision if $m_\chi$ significantly exceeds the mass of the heaviest target nucleus used.

Subjects: High Energy Physics – Phenomenology (hep-ph); Astrophysics (astro-ph)

Report number: KIAS-P08026

Cite as: arXiv:0803.4477v1 [hep-ph]

Submission history

From: Chung-Lin Shan [view email]

[v1] Mon, 31 Mar 2008 15:35:17 GMT (69kb)

http://arxiv.org/abs/0803.4477

ljk April 4, 2008 at 12:57

Searching for Neutrinos from WIMP Annihilations in the Galactic Stellar Disk

(Submitted on 3 Apr 2008)

Abstract: Weakly interacting massive particles (WIMPs) are a viable candidate for the relic abundance of dark matter (DM) produced in the early universe. So far WIMPs have eluded direct detection through interactions with baryonic matter. Neutrino emission from accumulated WIMP annihilations in the solar core has been proposed as a signature of DM, but has not yet been detected. These null results may be due to small scale DM density fluctuations in the halo with the density of our local region being lower than the average (around 0.3 GeV/cm^3 ). However, the accumulated neutrino signal from WIMP annihilations in the Galactic stellar disk would be insensitive to local density variations. Inside the disk, dark matter can be captured by stars causing an enhanced annihilation rate and therefore a potentially higher neutrino flux than what would be observed from elsewhere in the halo.

We estimate a neutrino flux from the WIMP annihilations in the stellar disk to be enhanced by more than an order of magnitude compared to the neutrino fluxes from the halo. We offer a conservative estimate for this enhanced flux, based on the WIMP-nucleon cross-sections obtained from direct-detection experiments by assuming a density of around 0.3 GeV/cm^3 for the local DM. We also compare the detectability of these fluxes with a signal of diffuse high energy neutrinos produced in the Milky Way by the interaction of cosmic rays (CRs) with the interstellar medium (ISM). These comparative signals should be observable by large neutrino detectors.

Comments: 8 pages, 3 figures, Submitted to MNRAS

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0804.0554v1 [astro-ph]

Submission history

From: Zacharia Myers [view email]

[v1] Thu, 3 Apr 2008 13:32:14 GMT (44kb)

http://arxiv.org/abs/0804.0554

ljk April 11, 2008 at 10:15

Movie Review | ‘Dark Matter’

The Cultural Divide, in Cosmology and Life

Reviewed by STEPHEN HOLDEN

“Dark Matter” is a movie of ideas that does an exemplary
job of translating scientific speculation into layman’s language.

Review:

Movie Details:

Showtimes:

Rate and Review:

http://movies.nytimes.com/movie/316636/Dark-Matter/rnr?8mu&emc=mu

ljk April 11, 2008 at 13:12

Dark Fluid: Towards a unification of empirical theories of galaxy rotation, Inflation and Dark Energy

Authors: HongSheng Zhao (SUPA, St Andrews) Baojiu Li (DAMTP, Cambridge)

(Submitted on 10 Apr 2008)

Abstract: Empirical theories of Dark Matter like MOND gravity and of Dark Energy like f(R) gravity were motivated by astronomical data. But could these theories be branches rooted from a more general hence natural framework?

Here we propose the natural Lagrangian of such a framework based on simple dimensional analysis and co-variant symmetry requirements, and explore various outcomes in a top-down fashion. Our framework preserves the co-variant formulation of GR, but allows the expanding physical metric be bent by a single new species of Dark Fluid flowing in space-time. Its non-uniform stress tensor and current vector are simply functions of a vector field of variable norm, resembling the 4-vector electromagnetic potential description for the photon fluid, but is dark (e.g., by very early decoupling from the baryon-radiation fluid).

The Dark Fluid framework naturally branches into a continuous spectrum of theories with Dark Energy and Dark Matter effects, including the $f(R)$ gravity, TeVeS-like theories, Einstein-Aether and $\nu\Lambda$ theories as limiting cases. When the vector field degenerates into a pure Higgs-like scalar field, we obtain the physics for inflaton and quintessence.

In this broad setting we emphasize the non-constant dynamical field behind the cosmological constant effect, and highlight plausible corrections beyond the classical MOND predictions. Choices of parameters can be made to pass BBN, PPN, and causality constraints.

The Dark Fluid is inspired to unify/simplify the astronomically successful ingredients of previous constructions: the desired effects of inflaton plus quintessence plus Cold DM particle fields or MOND-like scalar field(s) are shown largely achievable by one vector field only.

Comments: 7 pages, 1 fig, ApJ submitted

Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics – Theory (hep-th)

Cite as: arXiv:0804.1588v1 [astro-ph]

Submission history

From: HongSheng Zhao [view email]

[v1] Thu, 10 Apr 2008 08:56:11 GMT (25kb)

http://arxiv.org/abs/0804.1588

ljk April 15, 2008 at 9:04

Dark matter particle discovered?

ScientificAmerican.com April 14, 2008

The DAMA (DArk MAtter)
collaboration at the University of
Rome is reportedly expected to
announce this week improved
experimental evidence for the
identity of dark matter. Researchers
from Italy stirred up controversy
eight years ago when they announced
they had discovered the identity of
dark matter, the invisible stuff
that’s thought to make…

http://www.kurzweilai.net/email/newsRedirect.html?newsID=8417&m=25748

ljk April 22, 2008 at 16:19

A very interesting interview on this presumed dark matter
discovery from Cosmic Variance:

http://cosmicvariance.com/2008/04/21/guest-post-juan-collar-on-dark-matter-detection/

ljk April 25, 2008 at 9:49

Dark matter claims disputed

Flashes of light seen at the DAMA experiment in Italy are not
necessarily WIMPs, say physicists

http://physicsworld.com/cws/article/news/33870

ljk May 21, 2008 at 10:26

More Missing Cosmic Matter Found

Space.com May 20, 2008

After an extensive search,
astronomers say they have definitely
found half of the universe’s missing
normal matter in the spaces between
galaxies. “We think we are seeing
the strands of a web-like structure
that forms the backbone of the
universe,” said University of