Discovery of an arc of galaxies 3.3 billion light years away

An international team of astronomers from the United States and the United Kingdom discovered a giant, almost symmetrical arc of galaxies by observing absorption lines in the spectra of the Sloan Digital Sky Survey (SDSS) quasars .

The Giant Arc: the gray outlines represent the Mg II absorbers, which indicate the distribution of galaxies and clusters of galaxies; the blue dots represent the background quasars; the Giant Arc is centered on this number spanning -600 to +400 Mpc on the x axis. Image credit: Lopez et al.

The newly discovered arc of galaxies is located over 9.2 billion light years away in the constellation Boötes.

Called the Giant Arc, it spans about 3.3 billion light years in length and 330 million light years in width.

The structure is twice the size of the Great Wall of Sloan galaxies and clusters seen in the nearby Universe.

His discovery adds to an accumulated set of cautious challenges to the Cosmological Principle.

“The growing number of large-scale structures exceeding the size limit of what is considered theoretically viable is becoming increasingly difficult to ignore,” said Alexia Lopez, doctoral student. student at the Jeremiah Horrocks Institute at the University of Central Lancashire.

“According to cosmologists, the current theoretical limit is calculated at 1.2 billion light years, which makes the Giant Arc almost three times the size.”

“Can the Standard Model of Cosmology explain these huge structures in the universe as rare fluids, or is there more to it?” “

Lopez and his colleagues made the discovery by observing quasar-backlit magnesium (Mg) II absorption systems, which are distant super-luminous galaxies that emit extraordinary amounts of energy and light.

“A quasar acts like a giant lamp lighting up other galaxies, with the light eventually reaching us here on Earth,” Lopez said.

“We can use telescopes to measure the spectra of these quasars, which basically tell us how far the light from the quasars has traveled, and in particular where the light has been absorbed. “

“We can pinpoint where the light from the quasar has passed through the galaxies thanks to an Mg II doublet characteristic, which is a distinctive pair of absorption lines in the spectrum.”

“From this easily identifiable absorption ‘fingerprint’, we can map low-light matter that would generally go unnoticed due to its low emitted light compared to quasars. “

“When looking at them on such a large scale, we would expect to see a statistically smooth distribution of matter across the Universe, based on the cosmological principle introduced by Einstein to facilitate mathematics, that the Universe is isotropic and homogeneous.”

“This means that the night sky, when viewed at a sufficiently large scale, should look the same regardless of the locations of observers or the directions in which they are looking.”

“The giant arch that we see certainly raises more questions than answers because it can expand the notion of ‘big enough’. The key question is: what do we consider to be ‘big enough’?”

“We see the Giant Arc now, but in reality the data we are looking at shows the Universe as it was half its life ago, for the light is on its way, traveling towards us from billions of years ago. ‘years. So long ago, the Universe back then was about 1.8 times smaller than it is now. “

Astronomers presented the results this month to 238th Virtual Meeting of the American Astronomical Society (AAS).


AM Lopez et al. 2021. A giant arc in the sky. SAA 238, abstract # 111.01

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