Experimental Cosmology
The Experimental Cosmology group in the Milano-Bicocca’s Physics Department is active in measurements and observations of the Cosmic Microwave Background (CMB), galactic polarized emission, large scale cosmic structures, clusters of galaxies, and cosmic rays.
The CMB is the relic radiation of the hot early stages of the expansion of our Universe. In the faint anisotropies of its temperature and polarization maps is encoded the history of the early stages and evolution of the universe. Collecting its data allows us to measure the values of the cosmological parameters.
Today we have a “standard model of cosmology” and we are exploring the details of the model. In particular, efforts are underway to find gravitational radiation from the Big Bang, to determine the sum of the neutrino masses, to search for new particle species, to map out the earliest cosmic structures, and to measure the parameters of the fields that produced the Big Bang, to find potential deviation from known physics.
The Experimental Cosmology group is leader or partner of the LiteBIRD satellite, the LSPE experiment, the QUBIC telescope, the Cosmo experiment, the Simons Observatory telescopes in the Atacama desert, the ACT telescope, the BLAST balloon-borne telescopes. The group also participates to the AMS-02 experiment operating from the International Space Station for the detection of antimatter in cosmic rays, and to understand the formation of the Universe and search for evidence of dark matter.
Our research involves designing, building, and testing sensitive receivers and instruments, observing the cosmos from the ground, balloons, or
satellites, and analyzing data from those observations.
Cosmic structure formation
The current cosmological model of structure formation prescribes that during the Universe’s first billion years tiny fluctuations in the density field grew into a spider network of matter and gaseous filaments dubbed the “Cosmic Web”. The formation of galaxies that we see today began in the densest regions of the Cosmic Web where gas was first turned into stars. The later evolution of galaxies is regulated by gas infall from the Cosmic Web, it is balanced by feedback processe and is also affected by the local environment in which galaxies live.
We study the formation and evolution of galaxies by combining observations with world-class 8-10m telescopes and state-of-the-art theoretical and numerical models and simulations. Our group focuses on the study of the gaseous component of the Cosmic Web to unravel how this links to the physical properties of the galaxies and how gaseous feeding co-evolves with the galaxies star formation activity. We also investigate the three-dimensional distributions of Cosmic Structures and the build-up of dense galaxy environments over time.
As part of our research, we aim to address several fundamental questions:
- How do galaxies form within the Cosmic Web? What are the physical conditions for the formation of stars within the early, potentially dark, proto-galaxies?
- How do galaxies get their gas? What is the morphology and kinematics of the accreting gas and how does this affect the galaxy formation and evolution process?
- What are the physical and morphological properties of the Cosmic Web? How does this compare to our understanding of cosmological structure formation in the universe and what does it tell us about the nature of Dark Matter?
- What is the effect of dense environments on galaxy evolution and how does the galaxy population change as increasingly massive structures assemble over time?
More information is available on the COSMIB group page: www.cosmib.org
Compact objects and gravitational waves
Gravitational waves (GWs) —vibrations of the spacetime itself predicted by Einstein’s theory of general relativity— are now an observational reality. Direct detections of such feeble waves emitted by compact objects are allowing us to unveil an otherwise invisible Universe, promising a revolution in our understanding of the fundamental interactions in Nature and of the Universe itself. The detection of the first GW signal – GW150914 – from the collision of two stellar black holes by the LIGO and Virgo Scientific Collaborations kickstarted this revolution. The subsequent discovery of GW170817, the merger of two neutron stars accompanied by the emission of multi-coloured light, has further opened the frontier of the “multi-messenger” exploration of the Universe. The field is now going to be revolutionised by the launch of the the ESA’s Laser Interferometer Space Antenna (LISA), which aims at detecting low–frequency GWs that cannot be accessed from ground. LISA will target gigantic binary collisions of million-sun black holes that inhabit galaxies along the entire cosmic history. LISA will be in operation in the same time frame of third generation ground-based detectors such as the European Einstein Telescope (ET), promising to open a “multi-band” GW Astronomy era, that will give us an unprecedented view of the entire Gravitational Universe. Meantime, the International Pulsar Timing Array Experiment is in search of a very-low frequency GW background emerging from the stochastic superposition of signals emitted by over-massive black holes, using radio pulsars as high precision detectors.
We study how neutron stars and black holes merge by performing numerical simulations in general relativity; how stellar black holes form and evolve in dense stellar environments and how their spins are shaped by these processes; how double neutron stars and black hole-neutron stars binaries observed at the time of their coalescence outshine at radio to gamma-ray frequencies; how massive black holes in merging galaxies form and pair down to scales where GW radiation drives their inspiral toward coalescence; and ultimately how
multiple, overlapping signals both in LISA and ET from a plethora of sources will be disentangled to carry on with high fidelity parameter’s estimations necessary for unveiling their astrophysical nature.
As part of our research, we aim to address a number of key questions:
- What are the fundamental properties of the densest matter in the cosmos? How do quarks and gluons manifest in the cores of the most massive neutron stars?
- What is the physics of central engines powering the panchromatic electromagnetic counterparts to neutron star mergers? How do they relate to short GRBs?
- Are black holes and neutron stars the only ultra-compact objects in the Universe?
- What are the mass and spin demographics of black holes throughout the Universe? Do intermediate mass black hole exist in Nature and are they the seeds upon which the supermassive form?
- What is the precise value of the Hubble constant? Is dark energy fully described by a cosmological constant in Nature?
- Do GWs propagate from their sources in the same way as EM waves?