New members of a protocluster of galaxies, 13 billion years old, have been seen for the first time. What do we know about this family of galaxies from the ancient Universe?
New galaxies in an ancient cluster have been detected by astronomers using an array of instruments, including the Subaru, Keck, and Gemini Telescopes. This protocluster of galaxies, 13 billion years old, is the oldest such grouping ever found. At the time this protocluster formed, the Universe was the 800 million years old, just six percent of its current age.
In the modern Universe, galaxies clusters can contain hundreds or thousands of members, but how these structures form remains a mystery. In order to better understand contemporary clusters, astronomers carefully study protoclusters, dense systems of dozens of galaxies in the ancient Universe.
“A protocluster is a rare and special system with an extremely high density, and not easy to find. To overcome this problem, we used the wide field of view of the Subaru Telescope to map a large area of the sky and look for protoclusters,” said Yuichi Harikane, of the National Astronomical Observatory of Japan.
A map of the Universe created by the Subaru telescope revealed a potential protocluster, dubbed z66OD. Ancient galaxies seen here are huddled together at distances 15 times more concentrated than is typical for galaxies in that age of the Universe. Investigations of the region by astronomers using instruments at the Keck telescope and the Gemini north observatory in Hawaii confirmed the age of the protocluster.
“ Investigating the large scale structure is important for understanding galaxy formation, since there is observational evidence that galaxy properties depend on their environment,” researchers describe in The Astrophysical Journal.
Galaxies within z660D are forming at a tremendous rate — five times greater than similar galaxies during that age of the Universe.
“The galaxies in z66OD form stars very efficiently, probably because the large mass of the system helps it to collect a large amount of gas, the material for stars,” explains Darko Donevski of the SISSA Institute in Italy.
Galaxy clusters are bound together in groups through the force of gravity. These clusters, in turn, lay in superclusters, which are the largest structures ever detected by astronomers.
One of the objects in this cluster, Himiko, is a massive collection of stars discovered at the Subaru telescope in 2009 and named in honor of a legendary queen from Japan.
One unusual feature of the cluster is that the family of galaxies is not huddled around its largest member, as might be expected due to the effects of gravity.
“It is reasonable to find a protocluster near a massive object, such as Himiko. However, we’re surprised to see that Himiko was located not in the center of the protocluster, but on the edge 500 million light-years away from the center,” said Masami Ouchi of the National Astronomical Observatory of Japan and the University of Tokyo who discovered Himiko.
Recent observations reveal protoclusters can be home to massive galaxies hidden from view in visible light by gargantuan clouds of dust. Future observations using ALMA (the Atacama Large Millimeter/submillimeter Array), a vast collection of radio telescopes in Chile, could reveal unseen bodies in this ancient family of galaxies.
A second protocluster, z57OD, was also examined during this study, which looked at 179 galaxies.
Himiko the Space Blob
The Subaru Telescope on Mauna Kea in Hawaii scans every degree of the night sky within its sight, in a systematic sweep of the northern sky. Operated by the National Astronomical Observatory of Japan, this 8.2 meter telescope has been mapping celestial objects near and far since 1999.
Just six years ago, astronomers using the Hubble Space Telescope found three galaxies within a gas cloud encompassing Himiko.
“One of the most fascinating objects to emerge from the Subaru Telescope’s wide-field survey — Himiko — was discovered in 2009. Himiko, a ‘space blob’ named after a legendary queen from ancient Japan, is a simply enormous galaxy, with a hot glowing gaseous halo extending over 55,000 light-years,” Caltech reported in 2013.
Our own Milky Way galaxy is a member of the local group, containing approximately 50 galaxies. The local group spreads about 10 million light-years from one side to another, and our home cluster contains around 1.3 billion times as much mass as the Sun.
Himiko the Queen
Stories and records suggest the legendary queen Himiko ruled the Yamatai territory of Japan from 183–248 CE, at a time when Japan was divided into roughly 100 kingdoms spread around the islands. She is said to have led 30 of these city-states in a loose confederation, leading Chinese historians to name her as the leader of all Japan at the time.
Japanese myths says that Himiko withdrew herself from her subjects, remaining unmarried in a fortress with 1,000 women who served their leader. Himiko is said to have one male among her entourage who served as a liason to other governments, while her younger brother carried out many of the day-to-day operations of government.
She is known as a shamaness, a leader connected in a very personal sense with the spirit world, a claim that was common among leaders of Japan in that era.
When Himiko passed away, 100 slaves were sacrificed to accompany her in her tomb. Today, she is well known to the schoolchildren of Japan as a legendary leader.
Much of what we know of her comes through Chinese historical records. In the year 238, she is said to have sent an group of emissaries to China, who regaled Himiko with gifts of a title, a gold seal, 100 bronze mirrors, and more. This mission was followed by two later journeys in 243 and 247 CE. These trips would mark the final diplomatic contact between the two cultures for roughly four centuries.
Just as Himiko the queen attempted to tie together her culture with those in China, by studying the Himiko cluster, we may be able to better understand the nature of the early Universe.
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