A scientist duo from city-based Inter University Centre for Astronomy and Astrophysics (IUCAA), has studied primordial black holes that were born as a result of a tiny bump in the potential energy levels of the universe, at a time when it was expanding rapidly.
Primordial Black Holes (PBH) were formed during the Hot Big Bang phase. It is believed that they are formed as a result of collapsing radiations as opposed to the collapse of massive stars, which is the case of any other black holes.
The study jointly, performed by cosmologists Varun Sahni and Swagat Mishra, has confirmed that this marginal rise in potential energy resulted in birth of several PBHs and also emitted very powerful gravitational waves.
PBH can be massively large as 3000kms or be extremely tiny like nucleus of an atom.
Approximately 14 billion years ago before the commencement of the Hot Big Bang phase, the very young universe was found to be active and expanding at a highly accelerated rate. This exponential growth in its size, experts say, was fuelled by the presence of uniform energy field and density as the universe passed through the Cosmic Inflation phase.
According to the scientists, as time passes, this uniform energy prevailing in the Inflation Field wanes out. As a result, the universe resumes its normal decelerating rate.
“But, before the energy dies out completely, we noticed that there could be a marginal increase in the potential energy for a very brief time in the form of a bump, on to an otherwise dwindling energy-level graph. The potential energy of inflation could be higher just by 1 per cent, but significant enough to create vast difference in the densities,” explained Mishra, co-author of the study titled ‘Primordial Black Holes from a tiny bump / dip in Inflation potential’ published in Journal of Cosmology and Astroparticle Physics, last week.
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Gravity is normally attractive in nature. On what allowed the primitive universe to undergo rapid expansion, the duo said, was the Inflation field which contrarily possessed repulsive gravity. This pushed the universe to expand at a much faster rate than normal.
The universe had expanded to nearly 10^27 times its original size, that too, within just fraction of a second by the time Cosmic Inflation phase concluded. Thereafter, the remnant energy possessed by this gravitational force got converted mainly into photons (light) in addition to protons, electrons, neutrons and other particles.
As the universe continued to grow exponentially during the Cosmic Inflation phase, it sent across tiny quantum jitters, said Mishra.
These fluctuations, released in a specific fashion, when sufficiently large, slowly give birth to galaxies and stars. Among those that were significantly large, helped form PBHs.
When asked about the resultant of this energy bump and the suddenly created instability in density, he said, “ This bump in energy then produces PBHs besides triggering very strong gravitational waves. Further studies of gravitational waves emerging from PBHs could give deeper insights as to how the energy was decaying.”
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While not all declining energy showcased similar energy bumps, and hence, PBHs were not born in all instances, the authors highlighted.
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