October 23, 2013
Astronomers Discover The Most Distant Galaxy Yet In The Universe
Lawrence LeBlond for redOrbit.com - Your Universe Online
A team of Texas and California scientists have discovered the most distant galaxy to date, after searching through a database of nearly 100,000 galaxies imaged by the Hubble Space Telescope as part of the CANDELS survey.
Bahram Mobasher and Naveen Reddy of University of California, were part of the team who discovered this distant galaxy. They collaborated on the project with researchers from Texas A&M University, the University of Texas at Austin, the National Optical Astronomy Observatories and several other institutions around the country and abroad.
Mobasher and Reddy identified the very distant galaxy candidate sifting through deep optical and infrared images taken by Hubble. The distance of the galaxy was confirmed by the Keck Observatory in Hawaii.
"It's exciting to know we're the first people in the world to see this," said study coauthor Vithal Tilvi, a postdoctoral research associate at Texas A&M. "It raises interesting questions about the origins and the evolution of the universe."
The galaxy in question can be seen as it was just 700 million years after the Big Bang, at a time when the Universe was only about 5 percent of its current age, which is 13.8 billion years old. A paper on their discovery will be published in the October 24 issue of the journal Nature.
LOOKING INTO THE PAST
The team said in order to measure a galaxy this far away in a definitive way, spectroscopy, which measures how much the wavelength of a galaxy’s light has shifted towards the red-end of the spectrum as it travels from the galaxy to Earth, is a key method. This phenomenon is called “redshift.” Since the expansion velocity and distances of galaxies are proportional, the redshift gives astronomers a measure of the distance to galaxies.
“What makes this galaxy unique, compared to other such discoveries, is the spectroscopic confirmation of its distance,” said Mobasher. He explained that because light travels at about 186,000 miles per second, distant objects appear to us as they have looked in the past. The more distant we can push such observations, the farther into the past we can see, he added.
“By observing a galaxy that far back in time, we can study the earliest formation of galaxies,” he said. “By comparing properties of galaxies at different distances, we can explore the evolution of galaxies throughout the age of the universe.”
The team’s discovery was made possible by a new instrument known as MOSFIRE, which was commissioned on the Keck Telescope. Not only is MOSFIRE extremely sensitive, but it has been designed to detect infrared light – a region of the spectrum to where the wavelength of light emitted from distant galaxies is shifted – and could target multiple objects at a time. The latter feature in this case was the one that allowed the team to observe 43 galaxy candidates in just two nights, and also in higher detail than in previous studies.
Through their spectroscopic detections, the team was able to accurately gauge the distances of the galaxies by measuring a feature from the ubiquitous element hydrogen called the Lyman alpha transition. This element is detected in most galaxies that are observed more than a billion years from the Big Bang. But because the astronomers are probing earlier in time, the hydrogen emission line becomes increasingly difficult to see.
Of the 43 observed galaxies using MOSFIRE, the team only detected the Lyman alpha transition from one galaxy, z8-GND-5296, shifted to a redshift of 7.5.
The researchers believe they may have zeroed in on the era when the early universe shifted from an opaque state in which most hydrogen is neutral to a more translucent state in which most hydrogen is ionized. This period is referred to as the Era of Re-ionization.
“The difficulty of detecting the hydrogen emission line does not mean that the galaxies are absent,” said Reddy, an assistant professor of astronomy. “It could be that they are hidden from detection behind a wall of neutral hydrogen.”
Observations have shown how the galaxy is forming stars very rapidly, producing 300 Sun-like stars each year, whereas our Milky Way Galaxy is producing perhaps two or three per year. Another galaxy that lies in the part of the sky and is nearly as distant (redshift 7.2) has been found to also be producing a high number of stars each year.
“So we’re learning something about the distant universe,” said Steven Finkelstein at the University of Texas at Austin, who led the project. “There are way more regions of very high star formation than we previously thought. There must be a decent number of them if we happen to find two in the same area of the sky.”
“With the construction and commissioning of larger ground-based telescopes – the Thirty Meter Telescope in Hawai'i and Giant Magellan Telescope in Chile – and the 6.5 meter James Webb Space Telescope in space, by the end of this decade we should expect to find many more such galaxies at even larger distances, allowing us to witness the process of galaxy formation as it happens,” Mobasher noted.
Finkelstein said the technological advancements that have surfaced in recent years is a key reason astronomers are able to probe deeper into space and closer to the Big Bang than ever before.
The powerful new MOSFIRE spectrometer is 25 times more light-sensitive than others of its kind. It was installed at Keck in 2012. Also, Hubble was outfitted by astronauts with a new near-infrared camera in 2009 that allows the space-based telescope to see farther into the past than ever before.
Finkelstein and Texas A&M’s Casey Papovich are also working together on another major development that will allow astronomers to better study the mysterious dark energy that is believed to be driving the expansion of the universe. The world’s largest spectrograph is to be installed at the Hobby-Eberly Telescope in west Texas to aid in this study.
But even that will pale in comparison to the two universities’ collaboration to help build the massive Giant Magellan Telescope, which, when complete in 2020, will create images 10 times sharper than what Hubble produces currently.
"The Giant Magellan Telescope will revolutionize this research," Papovich said. "We are pushing the current telescopes to their limits and only seeing the brightest galaxies at these redshifts. It is slow-going with current telescopes. The GMT will have about five times the light gathering power of the biggest telescopes we're using now, and it will make the measurements we're doing that much easier. It will probably take the GMT to really understand the conditions in the very early universe."