The Japanese Institute of Space and Astronautical Science has chosen for its next strategic mission LiteBIRD, a small space observatory. Six researches of the Institute of Theoretical Astrophysics at UiO are involved in the international project.

LiteBIRD research group members Eirik Gjerløw (left), Ragnhild Aurlien, Ingunn Kathrine Wehus, Hans Kristian Kamfjord Eriksen and Unni Fuskeland.  Ranajoy Banerji is not present. Credit: Martina D'Angelo/UiO Bruk bildet.

The LiteBIRD name stands for Lite (Light) satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection. It is a planned small space observatory that aims to detect or constrain the footprint of the primordial gravitational wave on the Cosmic Microwave Background (CMB), the leftover thermal radiation from the Big Bang, in a form of polarization pattern called B-mode.

LiteBIRD is primarily a Japan Aerospace Exploration Agency (JAXA) experiment, with proposed support from the National Aeronautics and Space Administration (NASA), Canadian Space Agency (CSA) and various European national agencies, included the European Space Agency (ESA). 

In May 2019 the Institute of Space and Astronautical Science (ISAS) has confirmed that LiteBIRD completed activities planned during Prephase-A2, and has selected LiteBIRD as its next strategic large mission, scheduled to be launched in the late 2020s.

Global model for the early universe

At the Institute of Theoretical Astrophysics six researchers are involved in the project LiteBIRD, of which cosmologist Ingunn Kathrine Wehus is the local project leader. The institute takes part in the LiteBIRD Joint Study Group on foregrounds as external collaborators, and are represented in the European Steering Committee and the Interim Governance Board.

– In our cosmology group at ITA/UiO we are working towards a global model of the various components we can observe in the universe, both foreground signals from the Milky Way or our solar system, and background cosmological signals like the cosmic microwave background (CMB), the cosmic infrared background (CIB) or the large-scale distribution of matter. This model and project is called Cosmoglobe and has recently been funded by the ERC, says Wehus.

Another ERC-funded project is about time-domain Gibbs sampling (also known as Commander3), where cosmologists will work on the raw data from various experiments and try to eliminate the pollution from the final map products and cosmological parameters. This will be done by simultaneously fitting for instrumental, foreground, and cosmological parameters.

– We are particularly excited about the extra synergy effect we get from the combination of better foreground modelling (Cosmoglobe) and better instrument modelling (Commander3). For both these projects we will include data from current, future and previous experiments we are involved in, like COMAP, LiteBIRD, PASIPHAE, Planck and SPIDER, in addition to other publicly available data sets, says Wehus.

– Will improve the accuracy of other cosmological parameters

For a single density wave propagating in the direction of the arrow, an electron will always see hotter and colder photons in a direction parallel or perpendicular to the plane of this single wave (a plane at right angles to the arrow). Regardless of the direction of the density wave, only E-mode polarization patterns can be produced.

This illustration displays the mechanism by which density and gravitational waves produce E- and B-mode patterns in the polarization of the CMB. Credit: BICEP2 Collaboration

A single gravitational wave stretches and squeezes space in a direction perpendicular from it. Depending on the orientation of this stretch/squeeze motion, the gravitational wave is capable of producing either E- or B-mode polarization patterns (lower right on the figure). The structure of the universe at the moment the CMB was emitted is a large combinations of these density and gravitational waves.

– A polarization field can in general be divided into curl-free E-modes and divergence-free B-modes, but for the CMB only primordial E-modes have currently been detected. The best constraints on the curl-type (swirly-type) B-modes comes from Planck combined with BICEP2/Keck, which showed that the non-detected B-mode signal strength can at most be 6 % of the E-mode signal strength. LiteBIRD is designed to detect B-mode signals that corresponds to only 0.1 % of the E-mode signal, explains Wehus.

Maps of the polarized CMB's fluctuations contain the signature of gravitational waves from inflation, a period of rapid expansion of the universe 10−38 second after its formation. Detecting or constraining primordial gravity waves will teach us about the physics going on in the baby universe.

– LiteBIRD will also significantly improve the accuracy of other cosmological parameters, like the optical depth to re-ionization, which tells us when the first stars ignited, or the mass of neutrinos, some very light elementary particles whose mass has not been detected in laboratories, but which must have made up a substantial part of the content of the younger universe, explains Wehus.

Contact:

Ingunn Kathrine Wehus, associate professor at the Institute for Theoretical Astrophysics

Read more about Cosmoglobe and Wehus' research:

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