Primordial black holes and the search for dark matter from the multiverse

Primordial black holes and the search for dark matter from the multiverse

Fig1. Baby universes that branch off from our universe shortly after the big bang seem to us like black holes. (Credit : Kavli IPMU)

The Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) is home to numerous interdisciplinary projects that benefit from the synergy of a wide range of expertise available at the institute. One such project is the study of black holes that could have originated in the early universe before stars and galaxies were born.

Such primordial black holes (PBHs) may explain dark matter or a portion of it, be responsible for some observed gravitational waves, and seed supermassive black holes found in the center of our Milky Way and other galaxies. They can also play a role in the synthesis of heavy elements when they collide with and destroy neutron stars, thus releasing neutron-rich material. There is a particularly exciting possibility that the mysterious dark matter, which makes up the bulk of matter in the universe, consists of original black holes. The Nobel Prize in Physics in 2020 was awarded to a theorist, Roger Penrose, and two astronomers, Reinhard Genzel and Andrea Ghez, for their discoveries that confirmed the existence of black holes. Since it is known that black holes exist in nature, it makes a very attractive candidate for dark matter.

The recent advances in fundamental theory, astrophysics and astronomical observations in search of PBHs have been made by an international team of particle physicists, cosmologists and astronomers including Kavli IPMU members Alexander Kusenko, Misao Sasaki, Sunao Sugiyama, Masahiro Takada and Volodymyr Takhistov.

Primordial black holes and the search for dark matter from the multiverse

Fig2. Hyper Suprime-Cam (HSC) is a giant digital camera on the Subaru telescope (Credit : HSC Project / NAOJ)

To learn more about original black holes, the research team looked to the early universe for clues. The early universe was so dense that any positive density fluctuation of more than 50 percent would cause a black hole. However, it is known that cosmological disturbances that galaxies are sown are much smaller. Nevertheless, a number of processes in the early universe could have created the right conditions for the formation of black holes.

One exciting possibility is that primordial black holes could emerge from the ‘baby universe’ that emerged during inflation, a period of rapid expansion that is believed to be responsible for the sowing of the structures we observe today, such as galaxies and clusters of galaxies. During inflation, baby universes can branch off from our universe. A small baby (or ‘daughter’) universe would eventually collapse, but the large amount of energy released in the small volume causes a black hole to form.

An even more peculiar fate awaits a larger baby universe. When larger than a critical magnitude, Einstein’s theory of gravity allows the infant universe into a state that looks different from an observer inside and out. An internal observer sees it as an expanding universe, while an outside observer (like us) sees it as a black hole. In both cases, the large and the small baby universe are seen by us as primordial black holes, hiding the underlying structure of multiple universes behind their “event horizons”. The event horizon is a boundary below which everything, even light, is trapped and cannot escape from the black hole.

  • Primordial black holes and the search for dark matter from the multiverse

    Fig3. The Subaru Telescope in Hawaii. (Credit : NAOJ)

  • Primordial black holes and the search for dark matter from the multiverse

    Fig4. A star in the Andromeda galaxy is temporarily moving brighter than a primordial black hole in front of the star, focusing the light in accordance with gravity theory. (Credit: Kavli IPMU / HSC Collaboration)

In their paper, the team described a new scenario for PBH formation and showed that the black holes from the “multiverse” scenario can be found using the Hyper Suprime-Cam (HSC) of the 8.2 m Subaru Telescope , a giant digital camera – management of which Kavli IPMU played a crucial role – near the top of 4,200 meters from Mt. Mauna Kea in Hawaii. Their work is an exciting extension of the HSC search for PBH pursued by Masahiro Takada, a principal investigator at the Kavli IPMU, and his team. The HSC team recently placed important restrictions on the existence of PBHs in Niikura, Takada et. al. (Natural Astronomy 3, 524-534 (2019))

Why was the HSC indispensable in this research? The HSC has a unique ability to represent the entire Andromeda galaxy every few minutes. When a black hole moves through the line of sight to one of the stars, the gravity of the black hole bends the rays of light and makes the star appear brighter for a short period of time. The duration of the star’s illumination tells the astronomers the mass of the black hole. With HSC observations, one can simultaneously observe hundreds of millions of stars and cast a wide net for primeval black holes that may cross one of the line of sight.

The first HSC observations have already reported a very interesting candidate event corresponding to a PBH of the ‘multiverse’, with a black hole mass comparable to the mass of the Moon. Inspired by this first sign, and guided by the new theoretical understanding, the team conducts a new round of observation to expand the search and to provide a definitive test of whether PBHs from the multiverse scenario can account for all dark matter.


Looking for primordial black holes


More information:
Alexander Kusenko et al., Exploring primordial black holes from the multiverse with optical telescopes, Physical overview letters (2020). DOI: 10.1103 / PhysRevLett.125.181304

Provided by Kavli Institute for Physics and Mathematics of the Universe

Quotation: Older black holes and the search for dark matter from the multiverse (2020, December 28), detected on December 28, 2020 from https://phys.org/news/2020-12-primordial-black-holes-dark-multiverse. html

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