In order to enable an iCal export link, your account needs to have an API key created. This key enables other applications to access data from within Indico even when you are neither using nor logged into the Indico system yourself with the link provided. Once created, you can manage your key at any time by going to 'My Profile' and looking under the tab entitled 'HTTP API'. Further information about HTTP API keys can be found in the Indico documentation.
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Testing the rotational nature of the supermassive object M87* from the circularity and size of its first image [Note unusual time & day!]
(Stockholm U. and Nordita)
The Event Horizon Telescope (EHT) collaboration has recently released the first image of a black hole (BH), opening a new window onto tests of general relativity in the strong field regime. In this paper, we derive constraints on the nature of M87* (the supermassive object at the centre of the galaxy M87), exploiting the fact that its shadow appears to be highly circular, and using measurements of its angular size. We first consider the simple case where M87* is assumed to be a Kerr BH. We find that the inferred circularity of M87* excludes Kerr BHs with observation angle θobs≳45∘ for dimensionless rotational parameter 0.95≲a∗≤1 whereas the observation angle is unbounded for a∗≲0.9. We then consider the possibility that M87* might be a superspinar, i.e. an object described by the Kerr solution and spinning so fast that it violates the Kerr bound by having |a∗|>1. We find that, within certain regions of parameter space, the inferred circularity and size of the shadow of M87* do not exclude the possibility that this object might be a superspinar.