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2Physics Quote:
"Lasers are light sources with well-defined and well-manageable properties, making them an ideal tool for scientific research. Nevertheless, at some points the inherent (quasi-) monochromaticity of lasers is a drawback. Using a convenient converting phosphor can produce a broad spectrum but also results in a loss of the desired laser properties, in particular the high degree of directionality. To generate true white light while retaining this directionality, one can resort to nonlinear effects like soliton formation."
-- Nils W. Rosemann, Jens P. Eu├čner, Andreas Beyer, Stephan W. Koch, Kerstin Volz, Stefanie Dehnen, Sangam Chatterjee
(Read Full Article: "Nonlinear Medium for Efficient Steady-State Directional White-Light Generation"
)

Sunday, December 06, 2015

Heavy Dark Matter Ignition of Supernovae

Joseph Bramante

Author: Joseph Bramante

Affiliation: Department of Physics, University of Notre Dame, Indiana, USA.

Dark matter makes up most of the mass we observe in our universe. Dark matter's gravitational pull has been identified in the structure of galaxies, the expansion of the universe, and the bending of light through galactic clusters. However, the mass of each dark matter particle, and dark matter's non-gravitational interactions, are still a mystery.

Type Ia supernovae result when a white dwarf's atomic nuclei rapidly fuse, prompting an explosion that spews forth heavier, decaying atomic nuclei. The light released by these decaying nuclei over a hundred days is collected by astronomers, who have noticed a pattern: the maximum brightness of Type Ia supernova can be used to predict how quickly the supernova's light will fade. This is the sense in which Type Ia supernovae are "standard candles" that have been used to measure the accelerating expansion of our universe.

For decades scientists thought that type Ia supernovae were standard candles, because they originated from "Chandraskhar mass" white dwarfs. The Chandrasekhar mass is the maximum mass a white dwarf can have, before it will collapse under its own weight. Contradicting expectations, recent precision studies of type Ia supernovae have shown that many white dwarfs which produce type Ia supernovae are significantly lighter than Chandrasekhar mass [1]. This is a puzzle, that could be solved by heavy dark matter.

A recent paper [2] shows that if dark matter particles are one million times heavier than protons, then enough dark matter could collect into white dwarfs to initiate a period of dark matter collapse. The collapsing dark matter particles would ricochet against white dwarf nuclei fast enough to fuse them, thereby sparking type Ia supernovae.
Figure 1: A schematic indicating that heavier, denser white dwarves would be ignited by dark matter more quickly than lighter, less dense white dwarves.

One prediction of this scenario is that more massive white dwarfs would explode sooner than less massive white dwarfs. This is because heavier white dwarfs are denser, and so the dark matter would be gravitationally bound into a smaller region inside them. Dark matter collected into a smaller region would collapse sooner (see Figure 1). Spurred by this possibility, the author looked for, and found some evidence for heavier white dwarfs exploding sooner in existing type Ia supernovae data (see Figure 2).

There are some plausible, competing explanations for sub-Chandrasekhar mass type Ia supernovae. For example, merging white dwarf stars may precipitate nuclear fusion [3]. The upcoming dark matter search experiments XENON [4] and Lux-Zeppelin [5] could detect or rule out some models of supernova-igniting dark matter. Finally, there is another dramatic consequence of supernova-igniting dark matter: it would collapse neutron stars into black holes at the center of our galaxy, where dark matter is more abundant [6].
Figure 2: (click on the image to view with higher resolution) There is an apparent correlation between the age of stars surrounding supernovae and the supernovae's initial masses. The thick red crosses indicate collected type Ia supernovae data, taken from reference [7]. The solid and dashed lines indicate the predictions of some heavy dark matter models.

References:
[1] R. Scalzo et al. (The Nearby Supernova Factory), "Type Ia supernova bolometric light curves and ejected mass estimates from the Nearby Supernova Factory", Monthly Notices of the Royal Astronomical Society, 440, 1498 (2014). Abstract.
[2] Joseph Bramante, "Dark matter ignition of type Ia supernovae", Physical Review Letters, 115, 141301 (2015). Abstract.
[3] Dan Maoz, Filippo Mannucci, Gijs Nelemans, "Observational clues to the progenitors of Type-Ia supernovae", Annual Reviews of Astronomy and Astrophysics, 52, 107 (2014). Abstract.
[4] E. Aprile et al. (XENON100 collaboration), "Limits on spin-dependent WIMP-nucleon cross sections from 225 live days of XENON100 data",  Physical Review Letters, 111, 021301 (2013). Abstract.
[5] D.S. Akerib et al. (LZ collaboration), "LUX-ZEPLIN (LZ) Conceptual Design Report", arXiv:1509.02910v2 [physics.ins-det].
[6] Joseph Bramante, Tim Linden, "Detecting dark matter with imploding pulsars in the galactic center",  Physical Review Letters, 113, 191301 (2014). Abstract.
[7] Y.-C. Pan, M. Sullivan, K. Maguire, I.M. Hook, P.E. Nugent, D.A. Howell, I. Arcavi, J. Botyanszki, S.B. Cenko, J. DeRose, H.K. Fakhouri, A. Gal-Yam, E. Hsiao, S.R. Kulkarni, R.R. Laher, C. Lidman, J. Nordin, E.S. Walker, D. Xu, "The Host Galaxies of Type Ia Supernovae Discovered by the Palomar Transient Factory", Monthly Notices of the Royal Astronomical Society, 438, 1391 (2014). Abstract.

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