
<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Dear all, </div><div class=""><div class=""><br class=""></div><div class="">Astro Journal club continues this Wednesday at 3 p.m. (sharp) in the seminar room F-201 of the Physics Department. </div><div class=""><br class=""></div><div class="">Presenter: Krešimir Tisanić, mag. phys.</div><div class=""><br class=""></div><div class="">Authors: Hees et al. (2017)</div><div class=""><br class=""></div><div class="">Title of presentation: Testing General Relativity with Stellar Orbits around the Supermassive Black Hole in Our Galactic Centre</div><div class=""><br class=""></div><div class="">Abstract: </div><div class=""><div class="">We demonstrate that short-period stars orbiting around the supermassive black hole in our Galactic center can successfully be used to probe the gravitational theory in a strong regime. We use 19 years of observations of the two best measured short-period stars orbiting our Galactic center to constrain a hypothetical fifth force that arises in various scenarios motivated by the development of a unification theory or in some models of dark matter and dark energy. No deviation from general relativity is reported and the fifth force strength is restricted to an upper 95% confidence limit of <span class="aps-inline-formula"><span tabindex="0" class="MathJax_CHTML mjx-chtml" id="MathJax-Element-1-Frame" style="font-size: 13px;"><span class="mjx-math" id="MJXc-Node-1"><span class="mjx-mrow" id="MJXc-Node-2"><span class="mjx-mrow" id="MJXc-Node-3"><span class="mjx-mrow" id="MJXc-Node-4"><span class="mjx-mo" id="MJXc-Node-5"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.475em; padding-bottom: 0.61em;">|</span></span><span class="mjx-mi" id="MJXc-Node-6"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.206em; padding-bottom: 0.273em;">α</span></span><span class="mjx-mo" id="MJXc-Node-7"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.475em; padding-bottom: 0.61em;">|</span></span></span><span class="MJXc-space3 mjx-mo" id="MJXc-Node-8"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.273em; padding-bottom: 0.408em;"><</span></span><span class="MJXc-space3 mjx-mn" id="MJXc-Node-9"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.408em; padding-bottom: 0.34em;">0.016</span></span></span></span></span></span></span> at a length scale of <span class="aps-inline-formula"><span tabindex="0" class="MathJax_CHTML mjx-chtml" id="MathJax-Element-2-Frame" style="font-size: 13px;"><span class="mjx-math" id="MJXc-Node-10"><span class="mjx-mrow" id="MJXc-Node-11"><span class="mjx-mi" id="MJXc-Node-12"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.475em; padding-bottom: 0.273em;">λ</span></span><span class="MJXc-space3 mjx-mo" id="MJXc-Node-13"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.071em; padding-bottom: 0.34em;">=</span></span><span class="MJXc-space3 mjx-mn" id="MJXc-Node-14"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.408em; padding-bottom: 0.34em;">150</span></span></span></span></span></span> astronomical units. We also derive a 95% confidence upper limit on a linear drift of the argument of periastron of the short-period star S0-2 of <span class="aps-inline-formula"><span tabindex="0" class="MathJax_CHTML mjx-chtml" id="MathJax-Element-3-Frame" style="font-size: 13px;"><span class="mjx-mrow" id="MJXc-Node-18"><span class="mjx-mo" id="MJXc-Node-19"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.475em; padding-bottom: 0.61em;">|</span></span><span class="mjx-msub" id="MJXc-Node-20"><span class="mjx-base"><span class="mjx-mrow" id="MJXc-Node-21"><span class="mjx-mover" id="MJXc-Node-22"><span class="mjx-stack"><span class="mjx-over" style="height: 0.17em; padding-bottom: 0.06em; padding-left: 0.061em;"><span class="mjx-mrow" id="MJXc-Node-25" style="vertical-align: top;"><span class="mjx-mo" id="MJXc-Node-26"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.408em; padding-bottom: 0.34em;">˙</span></span></span></span><span class="mjx-op"><span class="mjx-mrow" id="MJXc-Node-23"><span class="mjx-mi" id="MJXc-Node-24"><span class="mjx-char MJXc-TeX-math-I" style="padding-top: 0.206em; padding-bottom: 0.273em;">ω</span></span></span></span></span></span></span></span><span class="mjx-sub" style="font-size: 9px; vertical-align: -0.325em; padding-right: 0.071em;"><span class="mjx-mrow" id="MJXc-Node-27"><span class="mjx-mtext" id="MJXc-Node-28"><span class="mjx-char" style="padding-top: 0.475em; padding-bottom: 0.206em;"><span class="mjx-charbox MJXc-font-inherit" style="padding-bottom: 0.371em; width: 2.143em;">S0-2</span></span></span></span></span></span><span class="mjx-mo" id="MJXc-Node-29"><span class="mjx-char MJXc-TeX-main-R" style="padding-top: 0.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