2013년 8월 16일 금요일

Galaxy Anatomy In Early Universe Was a 'Cosmic Zoo'



















The diversity of galaxies in the early universe was as varied as the many galaxy types seen today, a massive Hubble Space Telescope photos survey reveals.
The Hubble photo survey found that the assorted range of galaxy types seen today were also present about 11 billion years ago, meaning that the types of galaxies seen today, which astronomers described as a "cosmic zoo," have been around for at least 80 percent of the universe’s lifespan. The universe is estimated to be 13.82 billion years old.

At the heart of the new study is a galaxy classification system known as the Hubble Sequence. The research team found that this system still applied to galaxies 11 billion years ago. The research will appear upcoming edition of the Astrophysical Journal.

"This is a key question: when and over what timescale did the Hubble Sequence form?" study lead author BoMee Lee of the University of Massachusetts, said in a statement. "To do this you need to peer at distant galaxies and compare them to their closer relatives, to see if they too can be described in the same way."

The new study is part of the Hubble Space Telescope Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey, or CANDLES.

"The largest project in the history of Hubble, it aims to explore galactic evolution in the early universe and the very first seeds of cosmic stracture at less than 1 billion years after the Big Bang," Hubble officials said in a statement.

The Hubble Sequence divides galaxies into three types based on their appearance. Spiral galaxies in the prime of their lives are full of gas used in star formation. Once that gas runs out, they can transition into a somewhat blob-like elliptical galaxy.

A third type of galaxy in the sequence, known as a lenticular galaxy, represents a transitional phase between a middle aged spiral galaxy and an older elliptical galaxy. These kinds of galaxies have a bright bulge like an elliptical galaxy; yet maintain some spiral-like structure as their star-forming gas runs out.
Scientists observed these kinds of galaxies in the early universe.

"This is the only comprehensive study to date of the visual appearance of the large, massive galaxies that existed so far back in time," co-author Arjen van der Wel of the Max Planck Institute for Astronomy in Heidelberg, Germany said in a statement. "The galaxies look remarkably mature, which is not predicted by galaxy formation models to be the case that early on in the history of the universe."

While past research showed that these distinct types of galaxy morphology existed as early as 8 billion years ago, the new study extends that understanding back another 2.5 billion years.
"The Hubble Sequence underpins a lot of what we know about how galaxies form and evolve — finding it to be in place this far back is a significant discovery," Lee said.


Source of Article: Space.com