Gravitational waves from population III binaries

Tomasz Bulik, Izabela KowalskaUniversity of Warsaw, Poland

Krzysztof BelczyńskiLos Alamos National Laboratory, USA

What are population III stars?● First stars in the Universe● Metal free material● Galaxies at high redshifts are already

containing lots of metals

When?● High redshift z=10-15, maybe even up to 30!● WMAP: reionization of Universe, z~11● Can be connected with high redshift GRBs

Properties of Pop3 stars● Masses

– Stable up to 500-1000 Msun– Initial mass function different

● Evolution– No mass loss– H burning through CNO cycle on main sequence– Pair production instability, low masses -pulsations,

intermediate masses disruption, large masses – direct collapse

● End products – black holes up to 500Msun

Fryer etal

Binaries?● Simulations only● All stellar populations contain a large fraction of

binaries● Massive close binaries in the Galaxy: WR20a,

consist of two nearly 80 Msun stars almost in contact

● Metal free cloud collapse

A simulation of metal free cloud

Saigo, Matsumoto Umemura 2004

Evolution of Pop 3 binaries● Mass transfers: stability● Stellar structure● Mergers, disruptions● Production of BHBH binaries● Initial conditions: mass function, mass ratios,

orbital separations● Typical products: binaries of 100-300 M_sun

black holes

Detectability● Coalescences:

– Detectable in LIGO and VIRGO by the ringdown signal

● Stochastic background:– Could be detected by LISA– May be substantial in DECIGO

Model dependence● The level depends strongly on binary fraction● Low frequency part depends on initial periods● High frequency cutoff – masses of the compact

objects BHs● Some limits will be available:

– LIGO/VIRGO: coalescences– LISA: isotropic stochastic background

Summary● Compact object binaries background in

DECIGO band● Resolving – wealth of information of stellar

astrophysics, Pop 3 stars, star formation..● The level of the noise is probably higher than

just from the DNS!

log(f)