About 13.8 billion years ago, a significant event marked the origin of everything, everywhere, and everywhen, shaping the Universe as we know it.

The causes and the first moments of this event remain questions of deep curiosity for scientists, as does the formation of the first stars.

The First 10-33 Seconds

The exact length of the “Inflationary Period” is still unclear, but it is often represented as lasting a fraction of a second, typically 10^-33 seconds. This period was so brief that more of these moments could fit in a single second than there have been seconds since the explosion. Understanding the early Universe is challenging due to the extreme conditions that existed.

The Universe began incomprehensibly small, smaller than any known subatomic particle, and expanded in an incredibly short time. The densities and temperatures during this time were vastly higher than anything seen today.

To investigate these early conditions, scientists at the Center for Astrophysics | Harvard & Smithsonian travel to remote locations like the South Pole, where the dry air provides excellent conditions for observing the Cosmic Microwave Background (CMB). Instruments like BICEP3, the Keck Array, and the South Pole Telescope are designed to detect traces of Inflation in the CMB.

The Cosmic Dark Age

Hydrogen Clouds and Cosmic Signals

Large clouds of hydrogen emit radio waves at specific frequencies. By studying these signals, astronomers are able to measure the motion of galaxies.

In addition, LEDA, through a custom radio telescope, searches for faint signals from hydrogen formed during the end of the cosmic dark age, less than 100 million years after the explosion. This study aims to understand how the first galaxies, stars, and black holes emerged.

Simulating Star Formation

To complement this research, scientists at the CFA Institute for Theory and Computation run simulations of the early Universe, showing how hydrogen clouds grew large enough to form the first stars. These stars, likely much larger than our sun, burned through their fuel rapidly and often ended in a dramatic supernova, potentially forming black holes in the process. These black holes may have contributed to the supermassive black holes seen today in the centers of galaxies.

Looking Into the Distant Past

The Inflationary Period

The "Inflationary Period" following the explosion is theorized to have caused an incredible expansion of the Universe, growing it by a factor of 10^26 in less than a fraction of a second.

This rapid growth projected tiny quantum fluctuations into the vastness of the cosmos, creating variations in matter distribution that laid the foundation for the Universe’s structure.

As the Universe expanded, subatomic particles cooled and formed hydrogen atoms, allowing light to travel freely. This faint glow, the Cosmic Microwave Background (CMB), remains today as the oldest observable radiation from the Universe, originating when it was just 380,000 years old. The CMB still carries signatures of the Inflationary Period, offering a glimpse into the Universe's earliest moments.

Beyond Inflation

While the theory of Inflation is widely accepted, other theories propose different origins, such as a cosmic rebound from a previous collapse. Scientists continue to explore these ideas by conducting experiments and observations to determine the true origin of the Universe.

The Cosmic Dark Ages

After the Universe cooled enough for atoms to form, it transitioned from a hot, bright place into one that was cold and dark. Gravity amplified tiny differences in the distribution of gas, forming vast clouds of hydrogen and empty voids. As gravity caused these clouds to collapse, the first stars began to form.

Scientists hypothesize that the first stars were much larger and shorter-lived than those today. As these stars died, black holes might have formed in great numbers, potentially seeding the supermassive black holes that are found in the centers of galaxies today. The era is known as the "cosmic dark age," as there are no direct observations to test these hypotheses.

Scientists at the Center for Astrophysics | Harvard & Smithsonian have created the Large Aperture Experiment to Detect the Dark Ages (LEDA) to locate the formation of the first stars and black holes, providing insight into the conditions of the Universe before the birth of stars.