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SUMMARY:Bright sirens\, dark sirens and gravitational-wave cosmography
DTSTART;VALUE=DATE-TIME:20260710T050000Z
DTEND;VALUE=DATE-TIME:20260710T052000Z
DTSTAMP;VALUE=DATE-TIME:20261027T060742Z
UID:indico-contribution-804@indico.narit.or.th
DESCRIPTION:Speakers: Hyung Mok Lee (Seoul National Univ.)\nGravitational-
 wave observations of compact-binary coalescences provide a direct measurem
 ent of luminosity distance. If the redshift of the source can also be dete
 rmined\, these events can be used as standard sirens to construct a Hubble
  diagram and probe the expansion history of the Universe. In practice\, ho
 wever\, identifying the host galaxies of gravitational-wave sources is ext
 remely challenging because of their large sky-localization uncertainties. 
 GW170817 was an exceptional multi-messenger event: its electromagnetic cou
 nterpart enabled the identification of both the binary neutron-star nature
  of the source and its host galaxy. Most gravitational-wave events detecte
 d so far\, however\, are binary black-hole mergers\, which are not expecte
 d to produce detectable electromagnetic radiation. These “dark sirens”
  therefore lack direct host-galaxy identification\, and statistical method
 s using galaxy catalogs have so far yielded only limited constraints on th
 e Hubble constant.\nThis situation could change dramatically with gravitat
 ional-wave detectors sensitive to frequencies lower than those accessible 
 to current ground-based observatories. If inspiraling binary black holes c
 an be observed from frequencies around 0.1 Hz\, the signals may remain in 
 band for weeks to months before merger. Over such long observation times\,
  the changing orientation and velocity of the detector due to the Earth’
 s rotation and orbital motion induce characteristic modulations in the gra
 vitational-wave signal. These modulations can significantly improve measur
 ements of both the luminosity distance and sky position of the source.\nSe
 veral detector concepts targeting the mid-frequency gravitational-wave ban
 d have been proposed. We show that such detectors could localize some dark
  sirens with sufficient accuracy\, in both sky position and distance\, to 
 uniquely identify their host galaxies. This would enable the construction 
 of an accurate gravitational-wave Hubble diagram independent of traditiona
 l electromagnetic distance indicators\, opening a new route to measuring t
 he cosmic expansion history.\n\nhttps://indico.narit.or.th/event/236/contr
 ibutions/804/
LOCATION:National Astronomical Research Institute of Thailand (NARIT) Andr
 omeda Meeting Room
URL:https://indico.narit.or.th/event/236/contributions/804/
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