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Oldest Galaxies In The Universe Discovered Around The Milky Way

By Alexandra Lozovschi
Published on: 23:04 PST, Aug 16, 2018

Some of the earliest galaxies to have formed in the universe lie “on our cosmic doorstep,” reports the BBC. The discovery belongs to a team of astronomers from Durham University in the U.K. and the Harvard-Smithsonian Center for Astrophysics in Cambridge (CfA), U.S., who uncovered that some the faintest satellite galaxies floating around the Milky Way are among the first ones to appear after the Big Bang.

This spectacular find is described in an exciting new study published yesterday in the journal Astrophysical Journal.

The researchers examined the smaller companions of larger galaxies, such as the Milky Way, Andromeda, and even the Large Magellanic Cloud, based on their luminosity function, or the total amount of radiated energy. What they found out is absolutely “mind blowing,” notes USA Today.

As it turns out, the tiny dwarf galaxies orbiting the Milky Way, including Segue-1, Bootes I, Tucana II, and Ursa Major I, are around 13 billion years old. In fact, these satellite galaxies are so ancient they were among the very first to spark into existence when the universe was still in its infancy, explains the Harvard-Smithsonian CfA.

“For some of these tiny satellites, maybe 50 percent or even 90 percent of their mass was assembled at a time when the universe was less than one billion years old. Their age today would be on the order of 13 billion years,” said study lead author Dr. Sownak Bose, an astronomer at the Harvard-Smithsonian CfA.

According to Durham University, the ancient dwarf galaxies surrounding the Milky Way are grouped into two separate populations, depending on the characteristics of their luminosity function.

The first population is extremely faint and includes the very first galaxies that were created. This group was formed during the “cosmic dark ages” — a cooling phase which began some 380,000 after the Big Bang and lasted for about 100 million years — after the very first hydrogen atoms that coalesced into clouds of dark matter got cool and unstable enough to begin churning out stars.

The second population of ancient galaxies is slightly brighter and formed after a gap of hundreds of millions of years — the length of time it took for hydrogen atoms to cool down again and come together in even bigger dark matter halos.

Once these first galaxies were born, they turned on the light for the entire universe, bringing an end to the darkness that spawned them. These bright objects (by comparison with everything else that existed before them) flooded the universe with intense ultraviolet radiation, destroying the rest of hydrogen atoms by knocking out their electrons — a process known as ionization.

This stopped all star-forming activity for a period of up to a billion years, or until the halos of dark matter became massive enough that even ionized hydrogen was able to cool down. The universe then plunged into its next cosmological phase, dubbed the reionization period, when the larger and brighter galaxies began to take shape — all “culminating in the formation of spectacular bright galaxies like our own Milky Way,” sates Dunham University.

Study co-author Carlos Frenk, director of the Institute for Computational Cosmology at Durham University, described the discovery as “hugely exciting.”

“Finding some of the very first galaxies that formed in our universe orbiting in the Milky Way’s own backyard is the astronomical equivalent of finding the remains of the first humans that inhabited the Earth.”

As he pointed out, the results support “the current model for the evolution of our Universe, the ‘Lambda-cold-dark-matter model’ in which the elementary particles that make up the dark matter drive cosmic evolution.”

Such ancient dwarf galaxies are to be found throughout the universe and might actually be more numerous than their bigger, brighter counterparts, notes the BBC. The team managed to zero in on this particular group orbiting the Milky Way primarily due to their proximity to us. Yet many similar discoveries could turn up in the future.

“If you go and examine these primitive galaxies, you should find bizarre things about them. Being the first ones, they should have properties that are unique to them,” said Frenk.

For instance, astronomers speculate that these ancient, pre-reionisation galaxies are more compact.

“They were formed at a time when the universe was much denser, because the universe was smaller,” explained Bose.

According to the sources, the findings were corroborated by a galaxy formation model that the team had previously developed and which showed the new data fit perfectly with the astronomers’ predictions.

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