Some Of The First Galaxies In The Universe Lurk Just Outside Earth’s Cosmic Neighborhood
Physicists have discovered a handful of the very first galaxies that formed in the universe — and they're relatively near Earth.
It's not quite within humans' reach, but new research reveals that these satellite galaxies are orbiting just outside the planet's neighborhood, the Milky Way.
In the study published in The Astrophysical Journal, physicists suggest that Segue-1, Bootes I, Tucana II, and Ursa Major I are all more than 13 billion years old.
"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," Carlos Frenk, the director of Durham University's Institute for Computational Cosmology, says in a statement.
History Of The Universe
The universe is widely believed to have formed the very first atoms when it was about 380,000 years old. It settled into a cooling period called the "cosmic dark ages," when the atoms accumulated into halos of dark matter for 100 million years.
Over time, the cooled gas inside these halos became unstable and formed stars. These made up the earliest ever galaxies in the universe, ushering in light into the formerly dark cosmos.
Early Galaxies vs Late Galaxies
The researchers first noticed that there are two types of satellite galaxies orbiting the Milky Way, their difference being in their luminosity. One group appears to be very faint and believed to have formed during the so-called cosmic dark ages, while the other set of satellite galaxies are brighter and formed hundreds of millions of years later.
According to Gizmodo, the scientists believe that galaxies began forming with the dawn of the first stars. However, when the atoms were "re-ionized" by the ultraviolet radiation that burst from the massive supernovae of these original stars, the universe became too hot for new galaxies to form.
It took hundreds of millions of years before the universe became cool enough again to churn out fresh galaxies.
"We think that cosmic re-ionization is one of the main phenomenon that happened in the history of the Universe early on," Azadeh Fattahi, a researcher at Durham University, says to Gizmodo. "Being able to see the footprints of that in the nearby Universe is quite exciting."
Fattahi is not involved in the study, but he has collaborated with the study authors.
As Frenk points out, their new research findings are consistent with a current model of the universe's evolution, which is called the Lambda-cold-dark-matter model. In this widely accepted model, cosmic evolution is driven by dark matter's elementary particles.
Sownak Bose, another study author and a research fellow at the Harvard-Smithsonian Center for Astrophysics, adds that it's remarkable that their work was able to bridge the gap between an existing theoretical model and actual data.