September 6, 2012
Hydrogen Atoms Can Help Astronomers See Into Our Galactic Past
April Flowers for redOrbit.com - Your Universe Online
If the eyes are the windows to your soul, the stars are the windows to our galactic past because they can unveil the history of our Universe. The farther away a star is, the older it is.
The Universe is estimated to be 14 billion years old, but our current telescopes can only see galaxies about 700 million years old and only then when the galaxy is unusually large or as the result of a big event like a stellar explosion.
An international team of researchers, led by Tel Aviv University, has developed a method for detecting galaxies of stars that formed when the universe was in its infancy, during the first 180 million years of its existence. Prof. Rennan Barkana of TAU's School of Physics and Astronomy says that this method is able to observe stars that were previously believed too old to find.
The research team's method, published in Nature, uses radio telescopes to seek out radio waves emitted by hydrogen atoms, which were abundant in the early days of the universe. The atoms emitted waves measuring about eight inches long, which reflect the radiation of the stars, making their emission detectable by radio telescopes. This development opens the way to learning more about the universe's oldest galaxies.
According to Bakana, these waves show a specific pattern in the sky. This pattern is a clear signature of the early galaxies, which were one-millionth the size of galaxies today. Differences in the motion of dark matter and gas from the early period of the universe affect the formation of stars and produce a specific fluctuation pattern that makes it much easier to distinguish these early waves from bright local radio emissions.
Researchers began to piece together a rough map of the galaxies in an area of the sky using the intensity of the waves, which is dependent on the temperature of the gas. If the gas is very hot, it means there are many stars there; if cooler, there are fewer stars.
These initial steps into the origins of the universe will allow radio astronomers to reconstruct what the early universe looked like for the first time. This is specifically true in terms of the distribution of stars and galaxies across the sky.
This field of astronomical research, now being called "21-centimeter cosmology," is just getting underway. Five different international collaborations are building radio telescopes to detect these types of emissions, currently focusing on the era around 500 million years after the Big Bang. Equipment can also be specifically designed for detecting signals from the earlier eras, says Prof. Barkana. He hopes that this area of research will illuminate the enigmatic period between the birth of the universe and modern times, and allow for the opportunity to test predictions about the early days of the universe.
"We know a lot about the pristine universe, and we know a lot about the universe today. There is an unknown era in between when there was hot gas and the first formation of stars. Now, we are going into this era and into the unknown," says Prof. Barkana. He expects surprises along the way, for example involving the properties of early stars, and that observations will reveal a more complicated cosmological reality than was predicted by their models.