Two weeks of news in one!
Astrophysics and Gravitation:
Did We Already Have the Data to Show Dark Matter Annihilation?
Dan Hooper, & Lisa Goodenough (2010). Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope arXiv arXiv: 1010.2752v1
Analyzing old data from the Fermi Gamma Ray Space Telescope, the authors have noticed gamma ray emissions consistent with predictions for a certain type of dark matter. Unfortunately, these things are never nice, clear problems where they’ve definitely seen dark matter or have definitely not seen it, but it’s an exciting collection of data points for astrophysicists who are on the dark matter hunt. It could turn out to be the evidence that people have been looking for, but it’s too early to say anything definitively.
Weighing Planets with Pulsars
Champion, D., et al. (2010). MEASURING THE MASS OF SOLAR SYSTEM PLANETS USING PULSAR TIMING The Astrophysical Journal, 720 (2) DOI: 10.1088/2041-8205/720/2/L201
What can’t pulsars do? The team, using an array of pulsars (PSRs J0437–4715, J1744–1134, J1857+0943, J1909–3744), have identified the masses of the planetary system from Mercury to Saturn, in agreement with the best-known masses determined by spacecraft and other observations. This new method relies on the incredibly predictable nature of pulsars and solar system ephemeris (the past and future positions of the Sun, Moon, and nine planets in three-dimensional space).
From the authors:
While spacecraft are likely to produce the most accurate measurements for individual solar system bodies, the pulsar technique is sensitive to planetary system masses and has the potential to provide the most accurate values of these masses for some planets.
For more, see A New Way to Weigh Planets.
A New Standard Candle?
Poznanski, D., Nugent, P., & Filippenko, A. (2010). TYPE II-P SUPERNOVAE AS STANDARD CANDLES: THE SDSS-II SAMPLE REVISITED The Astrophysical Journal, 721 (2), 956-959 DOI: 10.1088/0004-637X/721/2/956
For years, Type Ia supernovae have been used as standard candles to measure cosmic distances; they were especially important for the measurements that determined that the expansion of the universe ws accelerating. Now, some astrophysicists are suggesting that for even higher accuracy, we use Type II supernovae as well. Initially, Type II supernovae weren’t used as standard candles because we weren’t as sure about their properties and actual brightness as we were for Type Ia supernovae. Using additional markers to gauge cosmic distances could help confirm and strengthen current observations, as well as discover inconsistencies.
Adam Burrows, astrophysicist at Princeton University:
It is unlikely that this technique will be able to compete with Ia, but it can contribute complementary cosmic information. It is coming into its own.
For more, see Alternative yardstick to measure the universe.
Dark Matter in the Sun, Revisited
Lopes, I., & Silk, J. (2010). Neutrino Spectroscopy Can Probe the Dark Matter Content in the Sun Science, 330 (6003), 462-462 DOI: 10.1126/science.1196564
After being gravitationally captured, low-mass cold dark-matter particles (mass range from 5 to ~50 x 109 electron volts) are thought to drift to the center of the Sun and affect its internal structure. Solar neutrinos provide a way to probe the physical processes occurring in the Sun’s core. Solar neutrino spectroscopy, in particular, is expected to measure the neutrino fluxes produced in nuclear reactions in the Sun. Here, we show how the presence of dark-matter particles inside the Sun will produce unique neutrino flux distributions in 7Be- and 8B-, as well as 13N-, 15O-, and 17F-.
Finally, a credible sounding experiment to test this dark-matter-in-the-sun-hypothesis, discover that there is no cold dark matter in the sun, and convince people to stop taking things seriously just because they technically “could” be possible. We’re not 100% sure of the consistency of the moon either, therefore I propose it’s full of anaerobic unicorns.
New Oldest/Farthest Object in the Universe*
Lehnert, M., Nesvadba, N., Cuby, J., Swinbank, A., Morris, S., Clément, B., Evans, C., Bremer, M., & Basa, S. (2010). Spectroscopic confirmation of a galaxy at redshift z = 8.6 Nature, 467 (7318), 940-942 DOI: 10.1038/nature09462
Spectroscopic techniques have confirmed the sighting of a galaxy at redshift z = 8.6! Light from UDFy-38135539 is coming to us from 600 million years after the Big Bang, ie. z=8.6 means a light travel time of 13.1 billion years (comoving distance of around 30.5 billion light years) making it the oldest/farthest away object ever recorded. This is really exciting because we probably can not see older/farther objects with the current generation of telescopes so it could be a very long time before UDFy-38135539’s record is beaten.
*Not counting the CMB.
Inflation Predicts Universe Will End to Save Face
Raphael Bousso, Ben Freivogel, Stefan Leichenauer, & Vladimir Rosenhaus (2010). Eternal inflation predicts that time will end arXiv arXiv: 1009.4698v1
Yeah, I put this story after astronomy…
Present treatments of eternal inflation regulate infinities by imposing a geometric cutoff. We point out that some matter systems reach the cutoff in finite time. This implies a nonzero probability for a novel type of catastrophe. According to the most successful measure proposals, our galaxy is likely to encounter the cutoff within the next 5 billion years.
Ie. if we make a series of fairly wild assumptions, we end up with a high statistical likelihood that some type of major astronomical catastrophe will occur. Unfortunately, like any incredibly complex system, small errors in initial assumptions make any sort of numerical prediction meaningless here… so, no reason to be concerned at all. The universe could end in 1 year, 5 billion years, never, etc. We have no consistent or meaningful way to predict this yet.
High Energy Physics and Particles:
Indian Neutrino Observatory is a Go
The site for the $167m Indian Neutrino Observatory (INO) was approved this week by the Indian Ministry of Environment and Forests. This project will mean major things for the state of physics in India, and it will likely be the country’s largest scientific endeavour.
For more, see Green light for Indian neutrino observatory.
General Relativity, Quantum Gravity, et al.:
Experimental Search for Quantum Gravity
Sabine Hossenfelder (2010). Experimental Search for Quantum Gravity arXiv arXiv: 1010.3420v1
Physicist/blogger Sabine Hossenfelder has an interesting review piece on the phenomenological models that are used in quantum gravity as well as the experimental areas that they might be testable in. It’s a summary for those that are interested in what is being done right now in the experimental quantum gravity world.
Phenomenology of the Spatial Geometry of Loop Quantum Gravity
Major, S. (2010). Shape in an atom of space: exploring quantum geometry phenomenology Classical and Quantum Gravity, 27 (22) DOI: 10.1088/0264-9381/27/22/225012
If the title of this paper doesn’t sound exciting to you, I don’t know what does.
A phenomenology for the deep spatial geometry of loop quantum gravity is introduced. In the context of a simple model of an atom of space, it is shown how purely combinatorial structures can affect observations. The angle operator is used to develop a model of angular corrections to local, continuum flat-space 3-geometries. The physical effects involve neither breaking of local Lorentz invariance nor Planck-scale suppression, but rather only rely on the combinatorics of SU(2) recoupling. Bhabha scattering is discussed as an example of how the effects might be observationally accessible.
If you like symmetry breaking, quantization of the gravitational field, and geometry (and frankly, who doesn’t), you’ll probably enjoy this paper. It’s a fascinating study on the geometry, under some loopy assumptions, of the quantum world, and the mathematical peculiarities that effect our ability to observe it. Bonus: Seth Major also knows how to write accessibly too, for those who are field adjacent.
String Theory Makes Sense of Strange Metals
Sachdev, S. (2010). Holographic Metals and the Fractionalized Fermi Liquid Physical Review Letters, 105 (15) DOI: 10.1103/PhysRevLett.105.151602
We show that there is a close correspondence between the physical properties of holographic metals near charged black holes in anti–de Sitter (AdS) space, and the fractionalized Fermi liquid phase of the lattice Anderson model. The latter phase has a “small” Fermi surface of conduction electrons, along with a spin liquid of local moments. This correspondence implies that certain mean-field gapless spin liquids are states of matter at nonzero density realizing the near-horizon, AdS2×R2 physics of Reissner-Nordström black holes.
This amazing correspondence could lead to a unified model for understanding strange metals (thanks to string theory) that could result in numerous calculations, that were previously too hard to tackle, being solved by techniques already known in the black hole community
GR as a 3D Conformally Invariant Theory?
Henrique Gomes, Sean Gryb, & Tim Koslowski (2010). Einstein gravity as a 3D conformally invariant theory arXiv arXiv: 1010.2481v1
The authors have described an alternative description for the physical content/observable character of general relativity without the Lorentz invariant spacetime! Now most of you are probably thinking, “Well that sounds insane!”, and, I’d be inclined to agree, but it’s an interesting proposal. Basically, they’ve taken some ideas from Horava-Lifshitz gravity, such that the symmetries of their theory are identical to Horava-Lifshitz gravity in the high energy limit, but they’ve tried to smooth out all of the errors in the low energy limit (where Horava-Lifshitz looks nothing like general relativity). Have they made a Horava-Lifshitz-esque theory that is consistent with the physical nature of general relativity? That still remains to be seen, but it’s not obviously wrong. They’ve also provided a geometric picture, that could actually turn out to be more equivalent to the one from general relativity than expected, but it will take further study.
For more, see Einstein gravity as a 3D conformally invariant theory.
This “Week” in the Universe: October 12th – October 25th by PLOS Blogs Network, unless otherwise expressly stated, is licensed under a Creative Commons Attribution 4.0 International License.