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End date: 2021 × Start date: 2020 × DDC: 500 × WGL Institute: AIP ×

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    X-ray quasi-periodic eruptions from two previously quiescent galaxies
    (London [u.a.] : Nature Publ. Group, 2021) Arcodia, R.; Merloni, A.; Nandra, K.; Buchner, J.; Salvato, M.; Pasham, D.; Remillard, R.; Comparat, J.; Lamer, G.; Ponti, G.; Malyali, A.; Wolf, J.; Arzoumanian, Z.; Bogensberger, D.; Buckley, D.A.H.; Gendreau, K.; Gromadzki, M.; Kara, E.; Krumpe, M.; Markwardt, C.; Ramos-Ceja, M.E.; Rau, A.; Schramm, M.; Schwope, A.
    Quasi-periodic eruptions (QPEs) are very-high-amplitude bursts of X-ray radiation recurring every few hours and originating near the central supermassive black holes of galactic nuclei1,2. It is currently unknown what triggers these events, how long they last and how they are connected to the physical properties of the inner accretion flows. Previously, only two such sources were known, found either serendipitously or in archival data1,2, with emission lines in their optical spectra classifying their nuclei as hosting an actively accreting supermassive black hole3,4. Here we report observations of QPEs in two further galaxies, obtained with a blind and systematic search of half of the X-ray sky. The optical spectra of these galaxies show no signature of black hole activity, indicating that a pre-existing accretion flow that is typical of active galactic nuclei is not required to trigger these events. Indeed, the periods, amplitudes and profiles of the QPEs reported here are inconsistent with current models that invoke radiation-pressure-driven instabilities in the accretion disk5–9. Instead, QPEs might be driven by an orbiting compact object. Furthermore, their observed properties require the mass of the secondary object to be much smaller than that of the main body10, and future X-ray observations may constrain possible changes in their period owing to orbital evolution. This model could make QPEs a viable candidate for the electromagnetic counterparts of so-called extreme-mass-ratio inspirals11–13, with considerable implications for multi-messenger astrophysics and cosmology14,15.
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    Ultracold atom interferometry in space
    ([London] : Nature Publishing Group UK, 2021) Lachmann, Maike D.; Ahlers, Holger; Becker, Dennis; Dinkelaker, Aline N.; Grosse, Jens; Hellmig, Ortwin; Müntinga, Hauke; Schkolnik, Vladimir; Seidel, Stephan T.; Wendrich, Thijs; Wenzlawski, André; Carrick, Benjamin; Gaaloul, Naceur; Lüdtke, Daniel; Braxmaier, Claus; Ertmer, Wolfgang; Krutzik, Markus; Lämmerzahl, Claus; Peters, Achim; Schleich, Wolfgang P.; Sengstock, Klaus; Wicht, Andreas; Windpassinger, Patrick; Rasel, Ernst M.
    Bose-Einstein condensates (BECs) in free fall constitute a promising source for space-borne interferometry. Indeed, BECs enjoy a slowly expanding wave function, display a large spatial coherence and can be engineered and probed by optical techniques. Here we explore matter-wave fringes of multiple spinor components of a BEC released in free fall employing light-pulses to drive Bragg processes and induce phase imprinting on a sounding rocket. The prevailing microgravity played a crucial role in the observation of these interferences which not only reveal the spatial coherence of the condensates but also allow us to measure differential forces. Our work marks the beginning of matter-wave interferometry in space with future applications in fundamental physics, navigation and earth observation.