Scientists have discovered the most distant galaxy ever confirmed, whose light took just over 13 billion years to reach Earth, providing a snapshot of the early universe. The faraway system resides in the night sky just above the handle of the Big Dipper.
One curious trait about the record-breaker is that it forms stars at an incredible rate, about 330 per year — more than a hundred times faster than our Milky Way galaxy. This could be a trademark of the universe’s early days, when hydrogen gas for star formation was much more plentiful.
“We wanted to figure out how galaxies evolve,” said Steven Finkelstein, lead author and University of Texas at Austin astronomer. “One way to do that is to push back deeper and deeper into the history of the universe.” The study was published online Wednesday in the journal Nature.
At first, the landmark discovery was a little bit of a let-down, the scientists said.
The team of astronomers used images from the Hubble Space Telescope to identify 43 possible faraway galaxies and then used state-of-the-art spectrographic equipment at the W. M. Keck Observatory in Hawaii to confirm their distances. In the end, Finkelstein and his colleagues could only retrieve data from this lone galaxy.
“We were first excited, then a little disappointed because we only saw one, and then excited again,” he said. “We would have hoped for some number bigger than one.”
With advances in instrumentation technology, astronomers continue to stretch their detection capabilities further outward from the Milky Way. Because light takes time to travel such long distances, remote objects allow them to peer back through time.
Take the sun as a simple example, said study author and Texas A&M University astronomer Vithal Tilvi. Sunlight takes a little over eight minutes to reach Earth.
“That means that when we are looking at the sun, we are actually looking at the sun as it was eight minutes ago,” he said.
In comparison, the light detected from this outlying galaxy — with the official catalogue name z8-GND-5296 — left the galaxy 13.1 billion years ago. This gives us a glimpse of the universe as it was when it was only 700 million years old.
In other words, we’re looking 95 percent of the way back to the Big Bang. To put that into human terms, that would be like an 80-year-old watching a video of himself on his fourth birthday.
“From observing these distant galaxies, we can understand how the universe was when it was very young,” Tilvi said. “There’s no other way to look into the past.”
Setting out to find the most distant galaxy isn’t a single eureka moment, but rather a careful process of confirmation and remeasurement. Further-away galaxies than z8-GND-5296 have been identified but failed a double-check process along the way.
The team first perused a month’s worth of images from the Hubble telescope for possible candidate galaxies. Hubble avoids the snags that Earth-bound telescopes can run into, such as clouds and bad weather, to more easily spot the red blobs that signal a distant object.
The same effect that causes a passing ambulance siren to change pitch as it zooms by, called the Doppler shift, makes the most distant galaxies appear red. Because the universe is expanding, the galaxy’s light moves away from us and gets stretched into a redder wavelength.
“These galaxies from within the first billion years of the universe are so far away that they have shifted into the infrared, or redder than our eyes can see,” Finkelstein said.
How red the light of the object is gives some sense of how far away it is, but a technique called spectroscopy is the true litmus test that accurately confirms the distance. The researchers spent two days at the Keck Observatory, near the summit of the Mauna Kea volcano, looking for a characteristic piece of data called the Lyman-alpha emission line.
The Lyman-alpha line tends to be a bright signature of old-universe galaxies that are forming stars at a high rate. Once found for a particular galaxy, an exact distance from Earth can be calculated.
Although disappointing at first, finding only one Lyman-alpha line is an intriguing discovery, the scientists say.
One theory says that, after cooling down from the Big Bang, a cosmic fog of neutral hydrogen gas cloaked our early universe.
“That was the case until the very first galaxies lit up,” said Harvard University astrophysicist Avi Loeb, who was not involved in the study. “They produced the ultraviolet radiation that broke up hydrogen.”
Gradually, the universe started a “reionization” process — first with bubbles of ionization around individual stars, then dwarf galaxies. As those young galaxies grew in size and overlapped, they formed larger regions of ionization that eventually became today’s fully ionized universe.
“Perhaps we are seeing the evidence that it ended right around this galaxy,” Loeb said, and this one happened to peek through the fog where the other 42 candidates could not.
Loeb also believes the unusually high star-formation rate may have to be reconfirmed. Although there are other galaxies that birth hundreds of stars per year, they are often quite massive, while z8—GND—5296 is considered a dwarf galaxy.
“It’s not unusual to find small galaxies at those early times, but finding such a small galaxy making so many stars at once is unusual,” he said.
