Archive for astro-ph

Another Day at the ArXiv..

Posted in Cosmic Anomalies, The Universe and Stuff with tags , , , , , , , on October 8, 2009 by telescoper

Every now and again I remember that this is supposed to be some sort of science blog. This happened again this morning after three hours of meetings with my undergraduate project students. Dealing with questions about simulating the cosmic microwave background, measuring the bending of light during an eclipse, and how to do QCD calculations on a lattice reminded me that I’m supposed to know something about stuff like that.

Anyway, looking for something to post about while I eat my lunchtime sandwich, I turned to the estimable arXiv and turned to the section marked astro-ph, and to the new submissions category, for inspiration.

I’m one of the old-fashioned types who still gets an email every day of the new submissions. In the old days there were only a few, but today’s new submissions were 77 in number, only about half-a-dozen of which seemed directly relevant to things I’m interested in. It’s always a bit of a struggle keeping up and I often miss important things. There’s no way I can read as widely around my own field as I would like to, or as I used to in the past, but that’s the information revolution for you…

Anyway, the thing that leapt out at me first was an interesting paper by Dikarev et al (accepted for publication in the Astrophysical Journal) that speculates about the possibility that dust grains in the solar system might be producing emission that messes up measurements of the cosmic microwave background, thus possibly causing the curious cosmic anomalies seen by WMAP I’ve blogged about on more than one previous occasion.

Their abstract reads:

Analyses of the cosmic microwave background (CMB) radiation maps made by the Wilkinson Microwave Anisotropy Probe (WMAP) have revealed anomalies not predicted by the standard inflationary cosmology. In particular, the power of the quadrupole moment of the CMB fluctuations is remarkably low, and the quadrupole and octopole moments are aligned mutually and with the geometry of the Solar system. It has been suggested in the literature that microwave sky pollution by an unidentified dust cloud in the vicinity of the Solar system may be the cause for these anomalies. In this paper, we simulate the thermal emission by clouds of spherical homogeneous particles of several materials. Spectral constraints from the WMAP multi-wavelength data and earlier infrared observations on the hypothetical dust cloud are used to determine the dust cloud’s physical characteristics. In order for its emissivity to demonstrate a flat, CMB-like wavelength dependence over the WMAP wavelengths (3 through 14 mm), and to be invisible in the infrared light, its particles must be macroscopic. Silicate spheres from several millimetres in size and carbonaceous particles an order of magnitude smaller will suffice. According to our estimates of the abundance of such particles in the Zodiacal cloud and trans-neptunian belt, yielding the optical depths of the order of 1E-7 for each cloud, the Solar-system dust can well contribute 10 microKelvin (within an order of magnitude) in the microwaves. This is not only intriguingly close to the magnitude of the anomalies (about 30 microKelvin), but also alarmingly above the presently believed magnitude of systematic biases of the WMAP results (below 5 microKelvin) and, to an even greater degree, of the future missions with higher sensitivities, e.g. PLANCK.

I haven’t read the paper in detail yet, but will definitely do so. In the meantime I’d be interested to hear the reaction to this claim from dusty experts!

Of course we know there is dust in the solar system, and were reminded of this in spectacular style earlier this week by the discovery (by the Spitzer telescope) of an enormous new ring around Saturn.

That tenuous link gives me an excuse to include a gratuitous pretty picture:

It may look impressive, but I hope things like that are not messing up the CMB. Has anyone got a vacuum cleaner?


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