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The search for Dark Matter Using Black holes of the Early Universes (aka Multiverse)

When we read this topic, it would look like a bunch of words that seem to have no direct connection have ended up in one sentence by accident. But this is no accident at all. This scientific discovery was in fact made last year December by The Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU). This was one of their project where they studied black holes that could have made the early universe, much more before stars and galaxies we know today were born. Primordial black holes (PBHs) may very well account for all or at least a part of the dark matter that is responsible for some of the observed gravitational waves signals and even may initiate supermassive black holes found in the center of our galaxy and other galaxies. They could also play a role in the synthesis of heavy elements when they collide with neutron stars and destroy them, releasing neutron-rich material. In particular, there is an exciting possibility that the mysterious dark matter, which accounts for most of the matter in the universe, is composed of primordial black holes. 

Therefore, to learn more about primordial black holes, the research team looked at the early universe for clues. The early universe was very dense that any big positive density would create a black hole. A number of such processes could have made the right conditions to make black holes. One exciting possibility is that these primordial black holes could have formed during time periods of rapid expansion that is believed by scientists to have created the structures we see as galaxies today. During these time baby universes can branch off of the mother universe. A small younger universe might eventually collapse if not stable and eventually form a black hole. But something stranger happens to universes that are young, but older than the new born universes. If it’s bigger than a certain critical size, according to Einstein’s theory of gravity, it appears as two different states to an inside and outside observer. The inside observer will see it as an expanding universe, but an outside observer will see it as a black hole. In either case, both behave like primordial black holes. That hides their true nature behind their “Event Horizon”. The event horizon is a boundary below which everything, even light, is trapped and doesn’t escape. 

In the recent research thesis released by the research team they have described a scenario for these primordial black hole formation that shows that the black holes from the “Multiverse” scenario can be found using a special type of camera technology called Hyper Suprime-Cam (HSC). This camera type is very special because it has a unique capability to image the entire Andromeda galaxy every few minutes. If a black hole passes through the line of sight to one of the stars, the black holes Gravity bends the light rays and makes the star appear brighter than before for a short period of time. The time period for which the star’s brightness increase tells us the mass of the black hole. With this cameras observations we can observe over one million stars which increases the chance of us spotting a black hole. Some of the first HSC observations have already reported an interesting observation that might be a primordial black hole from the multiverse with a mass similar to that of our moon.

Words by - Vinuri Arambepola

Design by - Kasun Madushan