Astrophysics and cosmology with a decihertz gravitational-wave detector: TianGO

Abstract

We present the astrophysical science case for a space-based, deci-Hz gravitational-wave (GW) detector. We particularly highlight an ability in inferring a source's sky location, both when combined with a network of ground-based detectors to form a long triangulation baseline, and by itself for the early warning of merger events. Such an accurate location measurement is the key for using GW signals as standard sirens for constraining the Hubble constant. This kind of detector also opens up the possibility of testing type Ia supernovae progenitor hypotheses by constraining the merger rates of white dwarf binaries with both super-and sub-Chandrasekhar masses separately. We will discuss other scientific outcomes that can be delivered, including the precise determination of black hole spins, the constraint of structure formation in the early Universe, and the search for intermediate-mass black holes.

Neutron star mergers and how to study them

“…Minimum active detectors ) 1 70 ----70 ----2 4 2 4 9 ---9 1 4 9 ---3 19 44 34 --97 78 34 --4 8 26 41 24 -99 92 65 24 -5 3 13 31 36 17 100 97 84 53 17 For these rows, the fraction of time a given number of interferometers contribute is given in absolute terms in the central block and cumulative terms in the final block. Each individual interferometer is assumed to have a 70% livetime, which is a fiducial value based on prior results and future expectations 2008; Kawamura et al 2011;Canuel et al 2018;Mueller et al 2019;Kuns et al 2020). Such devices would measure BNS systems years before merger and are likely the only way to achieve good pre-merger localizations.…”

Spin and eccentricity evolution in triple systems: From the Lidov-Kozai interaction to the final merger of the inner binary

“…For example, if we could measure the angle between spin and orbit first with a spacebased detector in, e.g., the decihertz band (as demonstrated in Ref. [66]), and then again with a ground-based detector at its merger, then Eq. (64) and Fig.…”

“…The eccentricity is yet another interesting aspect that we explore in this study, as it usually bears unique signatures of a binary's formation channel [33,[54][55][56][57][58][59][60][61][62][63], and it is anticipated to be detectable by future space-based GW observatories in the millihertz and decihertz bands such as LISA [64], TianQin [65], and TianGO [66]. This motivates investigating the limiting eccentricity that can be excited by the LK mechanism and the observational consequences for future space-based and ground GW detectors.…”

“…as such, we use the (plus, dot, cross) markers to represent timestamps of (1 week, 1 day, 1 hour) prior to the merger. Also shown in the plot (cyan traces), from left to right, are the sky-averaged sensitivity curves 22 of LISA [64], TianGO [66], and LIGO-Voyager [92].…”

“…In the case of a milli-Hz detector, e.g., LISA, there is a potential loss of detection because when 2f orb is in the millihertz band (corresponding to the instant marked by the pluses), the GW is mostly carried away by the high-order harmonics [94] that oscillate at frequencies above LISA's sensitivity band. However, a detector sensitive to the decihertz band, e.g., the proposed TianGO mission [66] (middle cyan trace), could detect the evolution of these eccentric systems.…”