|
In This Issue...
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Astronomers Find Hundreds of Galaxies in Early Universe
|
|
Astronomers Find Hundreds of Galaxies in Early Universe
By Judith Wellner
The evolution of galaxies can take millions, even billions of years, spinning in a vast universe so big and taking so long to evolve that comprehension by humans is difficult at best.
Likewise, it is equally difficult for astronomers to witness dramatic changes or discover the rules governing this unique evolutionary process. However, some scientist are trying to do just that.
A team of astronomers, led by Rychard Bouwens and Garth Illingworth of UCSC, has found more than 500 galaxies that exited less than a billion years after the Big Bang. Their findings were presented on Aug. 17 at the 2006 General Assembly of the International Astronomical Union and published in the Sept. 14 issue of the journal Nature, as well as the Nov. 20 issue of the Astrophysical Journal.
The team used data collected by NASA’s Hubble space telescope. They primarily analyzed images of the Hubble Ultra Deep Field (HUDF), which is a composite of images of specific regions of space, accumulated over a period from September 2003 through January 2004. The Ultra Deep Field is the farthest-reaching image of the universe ever taken in visible light. The team also examined images from two other sections of the sky.
These areas are known as the Great Observatories Origins Deep Surveys (GOODS).
Exploring the Origins of Many Galaxies
The discovery takes us closer to an understanding of the origin of galaxies. Finding over 500 galaxies from the early days of the universe is a big leap in the field of cosmology.
Finding hundreds of galaxies is significant by itself. What makes the findings even more intriguing is that while the team found hundreds of bright galaxies around 900 million years after the Big Bang, they only found a very small number of them about 200 million years earlier.
This suggests that major changes took place in those 200 million years.
“This could help us understand even earlier times,” said Bouwens. “It’s like looking at human evolution by studying what a nine-year-old looks like and what a seven-year-old looks like and from this trying to trace back what, for instance, a four-year-old might look like.”
The formation of early galaxies is a territory that has challenged astronomers for decades but has produced very few results.
“There hasn’t been much known about galaxies at these very early times,” said Bouwens. “There’s a whole epic of the universe we didn’t know much about. It is very exciting, because it seems very dramatic. Finding a large number of galaxies during one time period and then not in another… it means we are observing galaxies during a period of rapid change.”
Universe Changing
In the beginning, the universe was much more homogenous than it is today. “The density was almost the same everywhere,” said Bouwens.
Then, as a result of gravitation, some areas became denser than others. And those parts continued getting denser over time.
“Gravitation over time pulled in enough matter to form stars,” Bouwens added.
After the Big Bang, it took about 100 to 200 million years for the first stars to begin to form.
“In the beginning, everything was very black, cold, and empty, with no visible light,” Bouwens explained. “Then stars were formed, then stars came together with other stars, and galaxies started growing from these very small seeds. Like the Milky Way. It started out just as a single star.”
Bouwens said that looking back in time is literally like looking into history.
“Telescopes are like time machines. The farther out we look the further back in time we’ll see,” said Bouwens.
The reason it is so hard to go back in time and see galaxies that existed millions of years ago is because as the universe is expanding, the frequency of light changes.
“The universe expands and it stretches the light,” explains Bouwens. “Once it was high frequency, but over time it shifts towards lower frequency.
Pushing back to the very beginning of the universe is difficult, because the light is very red-shifted.”
Lower frequency light occurs as a redder portion of the spectrum than higher frequency light, and therefore it requires special telescopes to detect it.
“You can’t see it unless you go [to the] infrared wavelength,” said Bouwens.
Most of the telescopes used for astronomical research do not have such capabilities. One of the reasons is that most telescopes work with optical lenses that cannot see infrared light. The other reason is that they tend to look at the sky from the ground, while the Hubble Telescope is orbiting in space.
“When you’re trying to see these distant galaxies from the earth, it’s very hard because the earth is warm, the atmosphere is warm, everything around us emits light in the infrared,” said Bouwens.
“For a similar reason we can’t see the stars when the sun is up.”
Space Telescope Opens Universe
On the other hand, when searching for galaxies using a space telescope, the environment is much colder, and it is therefore easier to detect infrared light.
“It’s more like looking at the stars during night-time,” Bouwens said.
The fact that the first galaxies were so small makes research even more challenging.
“If you go back, what you’re looking for will be very small. That’s why it’s so hard to find these galaxies,” said Bouwens. “It’s like looking for treasure.”
The Hubble Space Telescope was launched in 1990 and since then has been circling around the earth, taking images of various segments of the universe.
Many astronomers around the world have access to the images taken by the Hubble. But to become one of these privileged scientists is not an easy process.
“Astronomers around the world come up with ideas and submit proposals. Then a committee of astronomers look at it and decide what the telescope will look at,” said Bouwens.
The team was awarded several months of telescope time by NASA because Illingworth participated in building one of the cameras for the Hubble.
Since the team started the study in 2002, they have used a few weeks of telescope time each year.
The team is planning to continue the study, hoping to find further data that might explain how galaxies evolved in the early days of the universe.
“There’s still some data. We want to improve our study,” said Bouwens. “We want to go back as far in time as we can and then try to figure out what had happened at the earliest stages of galaxy development.”
Bouwens added that soon even better telescopes will be available for astronomers. The launch of the James Webb space telescope is scheduled for 2013.
“It will be bigger than the Hubble and will look way further back in time, to when the universe was 300 to 400 million years old.”
|
