3.3-Billion-Light-Year-Long Arc of Galaxies Discovered | Astronomy – Sci-News.com

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

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

The newly-discovered arc of galaxies is located more than 9.2 billion light-years away in the constellation of Botes.

Named as the Giant Arc, it spans approximately 3.3 billion light-years in length and 330 million light-years in width.

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

Its discovery adds to an accumulating set of cautious challenges to the Cosmological Principle.

The growing number of large-scale structures over the size limit of what is considered theoretically viable is becoming harder to ignore, said Alexia Lopez, a Ph.D. student in the Jeremiah Horrocks Institute at the University of Central Lancashire.

According to cosmologists, the current theoretical limit is calculated to be 1.2 billion light-years, which makes the Giant Arc almost three times larger.

Can the Standard Model of cosmology account for these huge structures in the Universe as just rare flukes, or is there more to it than that?

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

A quasar acts like a giant lamp shining a spotlight through 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 essentially tells us the journey that the quasar light has been through, and in particular where the light has been absorbed.

We can locate where the quasar light has passed through galaxies by a signature Mg II doublet feature, which is a distinctive pair of absorption lines in the spectra.

From this easily identified absorption fingerprint, we can map low luminosity matter that would usually go unseen due to its faint light emitted in comparison to the quasars.

When viewed on such a large scale, we expect to see a statistically smooth distribution of matter across the Universe, based on the Cosmological Principle introduced by Einstein to make the maths easier, that the Universe is isotropic and homogeneous.

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

The Giant Arc we are seeing certainly raises more questions than answers as it may expand the notion of sufficiently large. The key question is, what do we consider to be sufficiently large?

We are seeing the Giant Arc now, but in reality, the data were looking at show the Universe as it was half its lifetime ago because the light has been en route, traveling towards, us for billions of years. It was so long ago that the Universe at the time was about 1.8 times smaller than it is now.

The astronomers presented the results this month at the 238th virtual meeting of the American Astronomical Society (AAS).

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A.M. Lopez et al. 2021. A Giant Arc on the Sky. AAS 238, abstract # 111.01

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3.3-Billion-Light-Year-Long Arc of Galaxies Discovered | Astronomy - Sci-News.com