Dark energy stars disproven by Event Horizon images? I was reading about the hypothesis advanced by George Chapline and Robert Laughlin that black holes might actually be 'dark energy stars', regions where spacetime has undergone a phase transition (e.g. this lay article and this paper).
Does the black hole image produced by the Event Horizon Telescope Collaboration falsify this hypothesis for good?
Or the hypothesis may still be compatible with the data?
Disclaimer: I am not a physicist, so please take it into account in your answers. I am just curious about the topic and would love to hear some expert opinions on this idea.
 A: No. The image obtained by EHT does not falsify this hypothesis since this image is mainly an evidence of a photon sphere, rather than the event horizon of the black hole.
But the “dark energy star” (one of black hole proposed alternatives) is expected to have a normal photon sphere up to rather small distance from the would-be horizon. And so the image from the EHT is compatible with black hole and dark energy star and also with other proposed black hole alternatives that are characterized by clear photon sphere.
For an overview of the multitude of exotic compact objects (ECO, the general name for black hole alternatives) and observational prospects for understanding their precise properties see the following (Open Access) review:


*

*Cardoso, V., & Pani, P. (2019). Testing the nature of dark compact objects: a status report. Living Reviews in Relativity, 22(1), 4, 
doi:10.1007/s41114-019-0020-4
Regarding the EHT images specifically, in section 5.3 the authors state:

In particular, the Event Horizon Telescope Collaboration has very recently obtained a radio image of the supermassive BH candidate in M87 (Akiyama et al. 2019) and similar results for Sgr A* are expected soon. The Event Horizon Telescope images of Sgr A* and M87* in the millimeter wavelength so far are consistent with a point source of radius $r_0=(2−4)M$
  (Doeleman et al. 2008; Doeleman 2012; Johannsen et al. 2016; Akiyama et al. 2019), or
  $$ ϵ∼1. \tag{102}$$
  This corresponds to the size of the photon sphere, which as we described in Sect. 2 will be the dominant relevant strong-field region for these observations. The absence of an horizon will influence the observed shadows, since some photons are now able to directly cross the object, or be reflected by it. There are substantial differences between the shadows of BHs and some horizonless objects [most notably boson stars (Cunha et al. 2015, 2017b; Cunha and Herdeiro 2018)]. Nevertheless, because of large astrophysical uncertainties and the focusing effect for photons when $ϵ→0$
  [Eq. (9)], all studies done so far indicate that it is extremely challenging to use such an effect to place a constraint much stronger than Eq. (102) (Vincent et al. 2016; Cunha et al. 2018; Cardenas-Avendano et al. 2019).

The parameter $ϵ$ used in the quote is a measure of how close a given ECO is to a ordinary black hole of the same mass: $ϵ=1-2M/R$, where $M$ is the mass of the ECO and $R$ is its radius (or more generally the radius where ECO becomes significantly different than the black hole), so that $ ϵ \to 0$ corresponds to an unmodified black hole of general relativity.
