This Is the Deepest View Into the Universe That Has Ever Been Seen

The Very Large Telescope in Chile has taken the deepest spectroscopic survey of space ever, with astronomers focusing on the Hubble Ultra Deep Field.

The Hubble Ultra Deep Field might be one of the most famous images in astronomy. The deepest ever high-resolution observations by the venerable Hubble Space Telescope were published in 2004, and in a seemingly empty patch of sky, Hubble revealed nearly 10,000 galaxies, with some of them more than 13 billion light-years from Earth.

Now, astronomers with the Very Large Telescope in Chile have taken a new look at the Hubble Ultra Deep Field (HUDF) region, staring even deeper than Hubble to reveal 72 new galaxies, as well as measuring the distances and properties of 1,600 very faint galaxies.

The team of over 50 astronomers says that the new observations using the MUSE (Multi Unit Spectroscopic Explorer) instrument have provided new insights on star formation in the early universe by allowing them to study the motions and other properties of early galaxies. The new studies also show how ground-based observations can fully contribute to our understanding of the cosmos.

“MUSE has the unique ability to extract information about some of the earliest galaxies in the Universe — even in a part of the sky that is already very well studied,” said Jarle Brinchmann in a statement.

Brinchmann, an astronomer at the University of Leiden in the Netherlands and the Institute of Astrophysics and Space Sciences at CAUP in Porto, Portugal, is the lead author of one of 10 papers describing results from this survey.

“We learn things about these galaxies that is only possible with spectroscopy," he said, “such as chemical content and internal motions — not galaxy by galaxy but all at once for all the galaxies!”

This new data contains the deepest spectroscopic observations ever made. Spectroscopy analyzes an object's  light,  and allows astronomers to infer the physical properties of that object, such as temperature, mass, luminosity, composition and even velocity.

MUSE’s spectroscopic information was measured for 1600 galaxies, which is 10 times more than what has been “painstakingly obtained in this field over the last decade by ground-based telescopes,” as the team put it in one of their papers.

“MUSE can do something that Hubble can’t,” said the principal investigator of the team, Roland Bacon, from the Lyon Astrophysical Research Center in France, in a statement. “It splits up the light from every point in the image into its component colors to create a spectrum. This allows us to measure the distance, colors and other properties of all the galaxies we can see — including some that are invisible to Hubble itself.”

The HUDF region is in the constellation Fornax and is only a tenth of the size of the full moon. The astronomers specifically chose the this field of view to make their study, Brinchmann told Seeker.

“This is the best-studied spot on the sky,” he remarked, “thus we knew there was a lot of supporting data that would help us interpret our very deep observations.”

Brinchmann said being able to use the Hubble data along with the new data the team acquired was key in understanding their observations.

Hubble data “was very important for much of the analysis as it helped us disentangle objects that were blurred together by the Earth’s atmosphere,” he said via email. “In fact, in many ways it was a very mutually beneficial process — the value of the HST data are significantly enhanced by the information provided by MUSE, and without the HST data the MUSE results would be much less easy to interpret.”

The original HUDF image required 800 exposures taken over the course of 400 Hubble orbits around Earth, with a total exposure time of 11.3 days between Sept. 24, 2003 and Jan. 16, 2004. The new observations by MUSE were taken over the course of two years with a total of 137 hours of telescope time.

MUSE was able to detect galaxies 100 times fainter than in previous surveys, seeing galaxies of various ages, sizes, shapes, and colors. The smallest, reddest galaxies may be among the most distant known, existing when the universe was just 800 million years old. The larger, brighter, well-defined spirals and elliptical galaxies were active about a billion years ago. The new observations provide additional information about galaxies formation and evolution across time.

Additionally, the team found luminous hydrogen halos around galaxies in the early universe, which provides new information of how material flows in and out of early galaxies.

The 72 newly found galaxies are ones that shine only in Lyman-alpha light, a form of ultraviolet light that usually indicates extremely distant objects. This is perplexing because galaxies that shine in only one form of light have not been seen before. These galaxies are ripe for further study.

Brinchmann and his colleagues weren’t expecting to find new galaxies in their observations.

“We were surprised,” he said. “Finding new galaxies is in itself not so exciting — we find loads everywhere we look if no-one has looked there before. But this was the best-studied part of the sky, with the deepest images that have ever been obtained, and it was a real surprise that we could find new galaxies that were not visible in these ultra-deep images from Hubble. We had not quite expected to go deeper than Hubble, forced as we were to peer through the Earth’s atmosphere.”

Other studies in the series of papers include analyzing galaxy merger rates in the early universe, mapping the motions of stars, and looking at the role of faint galaxies during the cosmic reionization that took place between 150 million years and 650 million years after the Big Bang, when the first stars and galaxies were formed.