Astronomers discover vast ancient galaxies, which could shed light on dark matter

Rodiano Bonacci
Agosto 11, 2019

Most models don't predict such an abundance of massive galaxies so early in the evolution of the universe.

"This is the first time that such a large population of massive galaxies was confirmed during the first two billion years of the 13.7-billion-year life of the universe."
"These were previously invisible to us", Tao Wang, researcher at the University of Tokyo, said in a news release.

The team published their findings August 7 in the journal Nature. These galaxies are also intimately connected with supermassive black holes and the distribution of dark matter.

Previously, scientists' knowledge of the most distant (and therefore earliest) galaxies have come from their ultraviolet light, stretched into lower-wavelength infrared light by the expanding universe and imaged by telescopes like the Hubble Space Telescope.

As the universe expands, light passing through becomes stretched, so visible light becomes longer, eventually becoming infrared.

"The light from these galaxies is very faint with long wavelengths invisible to our eyes and undetectable by Hubble", explained Professor Kotaro Kohno.

'I have a long history with that facility and so knew it would deliver good results'.

The reason these galaxies were hidden from sight is that, while they were actively making stars, they also contained plenty of dust, which tends to block and obscure much of a galaxy's light. At this point, most of the information about the mechanisms of star formation has been collected from populations of galaxies observed in rest-frame ultraviolet light. Previous studies have tracked down the existence of some massive galaxies which are not visible in ultraviolet light, but majority have been classified as extreme starburst galaxies, and it is inferred that they are unlikely to represent most of the massive galaxies. Additional investigations with ALMA or NASA's James Webb House Telescope, launching in 2021, might assist cinch the galaxies' exact ages and roles in galactic evolution.

"Theoretical researchers will need to update their theories now", said Professor Kohno.

'Even so, it took further data from the imaginatively named Very Large Telescope in Chile to really prove we were seeing ancient massive galaxies where none had been seen before'. If our solar system were inside one of them and you were to look up at the sky on a clear night, you would see something quite different to the familiar pattern of the Milky Way.

'The greater density of stars means there would be many more stars close by appearing larger and brighter.

"But conversely, the large amount of dust means farther-away stars would be far less visible, so the background to these bright close stars might be a vast dark void".

The invention of such massive, star-forming galaxies when the universe was lower than 2 billion years outdated matches nicely with previous observations of huge, quiescent galaxies later in cosmic historical past.

Calculations show that many galaxies would be torn apart instead of rotating if they weren't held together by a large amount of dark matter.

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