We find that, for a very specific shape of a monolayer graphene sample, a general relativistic-like description of a back-ground spacetime for graphene's conductivity electrons is very natural. The corresponding electronic local density of states is of finite temperature. This is a Hawking-Unruh effect that we propose to detect through an experiment with a Scanning Tunneling Microscope.PACS numbers: 04.62.+v, 72.80.Vp Keywords: Quantum fields in curved spacetime, Symmetry and conservation laws, Electronic transport in graphene Graphene is an allotrope of carbon that was first theoretically posited[1] and then found to have an abundance of "unorthodox" properties[2], the understanding of which is appealing to condensed matter as well as high energy theorists, see, e.g., [3]. In this letter we show that graphene can serve as a realization of the Hawking-Unruh effect [4,5], namely of the most crucial prediction of quantum field theory (QFT) in curved spacetimes [6,7]. This effect (that is eluding direct observations since its proposal, nearly forty years ago), predicts that quantum fields in a spacetime with an horizon exhibit a thermal character due to the nature of the quantum vacuum and to the relativistic process of measurement. This is the first step towards a quantum theory of gravity and, as such, drives a huge amount of constantly ongoing research. The results of this letter are also timely for the current efforts of the condensed matter theory community, as a central issue in the ongoing studies of graphene is how the curvature of the sample modifies its electronic properties [8].As is by now well known, the special topology of graphene's Honeycomb lattice (two interpenetrating triangular lattices) is the reason of the effectiveness of the description of its electronic properties in terms of massless, neutral, (2+1)-dimensional, Dirac pseudoparticles [9]. Linearizing around the two inequivalent Fermi points (Dirac points), k, in configuration space and in the continuum approximationwhere σ ≡ (σ 1 , σ 2 ), σ * ≡ (−σ 1 , σ 2 ), σ i are the Pauli matrices, v F ≡ 3ηℓ/2 is the Fermi velocity (that will be set to 1) with η ≃ 2.7 eV the hopping parameter and ℓ ≃ 2.5Å the lattice spacing, and ψare twocomponent Dirac spinors, as appropriate for this 2+1-dimensional system (a and b are anti-commuting annihilation operators for an electron in the two sub-lattices). We do not consider short range scattering centres or any other effect mixing the two Fermi points, thus we discuss the physics around a single Fermi point, e.g. ψ ≡ ψ + . The corresponding action is Following the spirit of the condensed matter analogues of gravitational effects [11], and paying due attention to the 2+1 dimensions [12] and to the Weyl symmetry of the massless Dirac field description [13], in this work we shall use graphene as a physical realization of QFT in curved spacetimes. We shall identify a specific shape, the Beltrami

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We explore whether supermassive nonbaryonic stars ͑in particular boson, miniboson, and nontopological soliton stars͒ might be at the center of some galaxies, with special attention to the Milky Way. We analyze, from a dynamical point of view, what current observational data show, concluding that they are compatible with a single supermassive object without requiring it to be a black hole. Particularly, we show that scalar stars fit very well into these dynamical requirements. The parameters of different models of scalar stars necessary to reproduce the inferred central mass are derived, and the possible existence of boson particles with the adequate range of masses is commented upon. Accretion to boson stars is also briefly analyzed, and a comparison with another nonbaryonic candidate, a massive neutrino ball, which is also claimed as an alternative to the central black hole, is given. Both models are capable of explaining the nature of the object in Sgr A* without invoking the presence of a singularity. One difficult issue is why the accreted materials will not finally produce, in a sufficiently long time, a black hole. We provide an answer based on stellar disruption in the case of boson stars, and comment on several suggestions for its possible solution in neutrino ball scenarios. Finally, we discuss the prospects for the observational detection of these supermassive scalar objects, using the new generation of x-ray and radio interferometry satellites.