A pilot survey to unveil dormant black holes

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Casares Velázquez
Amount granted to the IAC Consortium
276.000,00 €

Black holes (BHs) are the pinnacle of extreme gravity. They are responsible for the most violent phenomena observed in the Universe, from long gamma-ray bursts, tidal disruption events to gravitational waves (GW). Despite the recent growth in extragalactic BH discoveries by LIGO-VIRGO, our knowledge of the seed BH population is severely hindered by the multiple evolutionary paths and our ignorance of BH formation physics. Galactic X-ray transients (XRTs), on the other hand, offer a unique laboratory of BH properties forged at solar metallicity, and yet our understanding of this population is strongly limited by small-number statistics, with only 20 confirmed BHs discovered after 5 decades of intensive scrutiny of the X-ray sky. Thus, the only way to advance our knowledge of the Galactic BH population requires the discovery of a large sample of quiescent BH XRTs through a new research methodology rather than simply waiting for them to go into outburst (which will take many decades to barely double the number). We have devised HAWKs (the HAlpha-Width Kilo-degree survey), a deep survey of the Galactic Plane to unveil hidden quiescent BH XRTs by exploiting a new approach: a novel photometric technique optimized to select targets with broad Halpha emission lines, the hallmark of deep BH gravitational fields. HAWKs will produce a large boost in statistics which will revolutionize our understanding of the BH Galactic distribution and mass spectrum, key properties to constrain BH formation, the equation of state of nuclear matter and evolutionary channels for GW sources. Through this project we propose to exploit mini-HAWKs, a pathfinder of a limited region of the Galactic Plane (~50 sqr deg) that will (1) demonstrate the feasibility of the HAWKs survey strategy and (2) measure the discovery rate of quiescent BHs. Mini-HAWKS is one of the only 4 Legacy Surveys approved for the JAST80 telescope at the Obs. de Javalambre (OAJ), with 400 h granted (see https://oajweb.cefca.es/observingtime/oaj_ls). Mini-HAWKS will not only be a proof-of-concept of HAWKs but, further, it will provide a unique catalogue of Halpha emitters, such as Cataclysmic Variables, Be stars, T Tauri, Symbiotic binaries, Planetary Nebulae, etc. to unprecedented depths that will allow a plethora of ancillary studies. Key to our project is the production of 3 customized Halpha filters, centered at 6463 Å and widths 35/150/350 Å, not currently available at the OAJ. Thanks to the support of CEFCA FITE2022 and IAC Severo Ochoa actions we have procured the required funds to build the filters before the survey commences, in Nov-Dec 2023. It will take between 2-3 years to complete mini-HAWKs and, through this project we will secure the necessary human resources and economic support for the successful execution and scientific exploitation of the survey.






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