Friday , December 3 2021

Astronomers discover huge ancient galaxies that could shed light on dark matter



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Astronomers have used the combined power of numerous astronomical observatories around the world and in space to find a treasure trove of previously unknown ancient massive galaxies. It is the first multiple discovery of its kind, and such an abundance of this type of galaxy contradicts contemporary models of the universe. These galaxies are also closely related to supermassive black holes and the distribution of dark matter.

The Hubble Space Telescope offers unprecedented access to the unprecedented universe, but even it is blind to some of the most fundamental parts of the cosmic puzzle. Astronomers at the Institute of Astronomy at the University of Tokyo have wanted to monitor objects that they have long suspected of being there, but Hubble cannot disclose. Newer generations of astronomical observatories have finally revealed what they have been looking for.

"This is the first time such a large population of massive galaxies has been confirmed in the first 2 billion years of the universe's 13.7 billion years. Before, they were invisible to us, ”says researcher Tao Wang. "This finding contradicts current models for this period of cosmic evolution and will help to add some details that are missing so far."

But how can something as big as a galaxy start?

"The light from these galaxies is very dim, with long waves, invisible to our eyes and undetectable by Hubble," Prof. Kotaro Kohno explained. "So we turned to the Atacama Large Millimeter / submillimeter Array (ALMA), which is perfect for watching things like that. I have a long history with this facility and so I knew it would produce good results. "

Although these galaxies were the largest of their time, their light was not only dim but also stretched because of their vast distance. As the universe expands, the light passing through it expands, so that visible light becomes longer, eventually becomes infrared. The amount of stretching allows astronomers to calculate how far something is, which also reveals how long the light has been emitted from an object.

"It was hard to convince our peers that these galaxies are as old as we suspected. Our initial suspicions of their existence came from the infrared data of the Spitzer Space Telescope, Wang said. "But ALMA has keen eyes and reveals details at submillimeter wavelengths, the best wavelengths to peek through the dust present in the early universe. However, additional data was needed from the imaginatively called Very Large Telescope in Chile to really prove that we see ancient massive galaxies where no one has seen before. "

Another reason these galaxies look so weak is that larger galaxies, even nowadays, tend to be dust-covered, which obscures them more than their smaller galactic siblings.

And what does the discovery of these massive galaxies mean?

"The more massive the galaxy is, the more massive is the supermassive black hole in its heart. So exploring these galaxies and their evolution will also tell us about the evolution of supermassive black holes, "Kohno said. "Massive galaxies are also closely linked to the distribution of invisible dark matter. This plays a role in shaping the structure and distribution of galaxies. Theoretical researchers will need to update their theories now. "

Astronomers are also interested in how these 39 galaxies are different from ours. If our solar system was inside one of them and you had to look up at the sky on a clear night, you would see something completely different from the familiar model of the Milky Way.

"As something, the night sky will look far more majestic. Higher star density means that there will be many more stars nearby, looking bigger and brighter, ”Wang explained. "But conversely, the high dust content means that distant stars will be far less visible, so the background of these bright, close stars can be a huge dark void."

As this is the first time such a population of galaxies has been discovered, the implications of their study are only now being realized. There may be many more surprises ahead.

"These gargantuan galaxies are invisible at optical wavelengths, so it is extremely difficult to do spectroscopy, a way to study stellar populations and the chemical composition of galaxies. ALMA is not good at this and we need something more, "Wang concluded. "I can't wait for upcoming observatories like the James Web Space Telescope to show us what these primary beasts are made of."

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