Hubble Spots Ancient Galaxy From Dawn of Time
This image from the Hubble Space Telescope CANDELS survey highlights the most distant galaxy in the universe with a definitively measured distance, dubbed z8_GND_5296. The galaxy's red color alerted astronomers that it was likely extremely far away, and thus seen at an early time after the Big Bang.
The Hubble Space Telescope's eXtreme Deep Field (XDF) was assembled by combining 10 years of Hubble photographs taken of a patch of sky at the center of the original Hubble Ultra Deep Field. The XDF is a small fraction of the diameter of the full moon.
Scientists on the hunt for the first galaxies formed after the universe’s creation have a new milestone -- an unexpectedly active galaxy that existed just 700 million years after the Big Bang.
The long-distance champ, known by its catalog number z8_GND_5296, first revealed itself in the Hubble Space Telescope’s infrared camera. Follow-up investigations with a new infrared light-splitting spectrograph at the Keck Observatory confirmed the galaxy’s location.
“If you tried to look at these really distant galaxies with a visible light telescope you would see nothing. Literally, they’re invisible. All that visible and optical light has been shifted into the near-infrared,” astronomer Steven Finkelstein, with the University of Texas at Austin, told Discovery News.
The shift, known as the Dopper effect, is due to the expansion of the universe and the speed at which the galaxies are moving away. It is similar to the shifting sound of an approaching train.
Oddly, z8_GND_5296 was the only one of 43 galaxy candidates that clearly radiated the telltale chemical fingerprint of a particular hydrogen emission astronomers needed for their celestial measuring sticks.
That in and of itself is fodder for a host of questions about the universe’s early years, particularly when and how quickly photons of light from the first galaxies could navigate intergalactic hydrogen gas without being scattered.
For light to be detected, the hydrogen needs to be ionized, a phenomenon that, somewhat paradoxically, is believed to have been triggered by the first generation of galaxies.
“To look at galaxies that are very distant is particularly interesting because light travels at a finite speed, so essentially the more distant a galaxy is the more time the light takes to get toward us. This means that by looking at distant galaxies we can probe the past history of the universe. We essentially see the galaxy at the point in time when the light was emitted,” astronomer Dominik Riechers, with Cornell University, told Discovery News.
“This galaxy is so far away that any light we receive from it travels for 13.1 billion years before it reaches us. What we’re really seeing is the universe as it looked like 13.1 billion years ago, which is only 700 million years of the Big Bang,” he said.
Aside from confirming z8_GND_5296’s extreme distance, the galaxy turned out to be producing stars at prodigious rate, pumping out the equivalent of 330 masses the size of the sun every year. That is more than 100 times the rate of star formation of the Milky Way galaxy.
“The early universe may harbor a larger number of intense sites of star formation that expected,” Finkelstein wrote in a paper published in this week’s Nature.
He and colleagues also were surprised by the galaxy’s unexpectedly high percentage of oxygen and other so-called metals -- elements heavier than hydrogen and helium.
The related discovery, made with NASA’s Spitzer space telescope, suggests that z8_GND_5296 contains the exploded remains of massive stars, whose nuclear furnaces forged the heavier elements, or that the area of space where the galaxy formed already was seeded with metals from a prior generation of stars -- perhaps the universe’s first.
“It’s surprising that so close to the Big Bang it’s already formed a decent fraction of its metal,” Finkelstein said.
The galaxy is about 1.3 billion times the mass of the sun and located in the direction of the constellation Ursa Major.
Previously, the most distant galaxy was one that formed about 740 million years after the Big Bang.
“We’re probing another 40 million years back into the history of the universe,” Finkelstein said.
Only one other object has been found to be more distant than z8_GND_5296 -- the explosion of a massive star about 70 million years earlier.
“The galaxy associated with this event has remained undetected,” Riechers noted.
To probe even farther back in time, astronomers are banking on NASA’s replacement for Hubble, the James Webb Space Telescope, which is due to launch in 2018.(Oct 23, 2013 01:00 PM ET // by Irene Klotz)
