Small galaxies in early universe packed same punch as present grown up ones

April 30th, 2008 - 1:18 pm ICT by admin  

Washington, April 30 (ANI): By observing compact galaxies in the universes distant past, astronomers have determined that though they were a fraction of the size of todays grownup galaxies, they contained approximately the same number of stars.

This finding was made by a team of astronomers, who used NASAs Hubble Space Telescope and the W.M. Keck Observatory on Mauna Kea, to study the galaxies as they existed 11 billion years ago, when the universe was less than 3 billion years old.

They found nine young, compact galaxies, each weighing in at 200 billion times the mass of the Sun.

The galaxies, each only 5,000 light-years across, are a fraction of the size of todays fully developed galaxies but contain approximately the same number of stars. In fact, each galaxy could fit inside the central hub of our Milky Way.

Seeing the compact sizes of these galaxies is a puzzle, said Pieter G. van Dokkum of Yale University in New Haven, Connecticut, who led the study. No massive galaxy at this distance has ever been observed to be so compact, he added.

According to Dokkum, it is not yet clear how they would build themselves up to become the large galaxies we see today.

They would have to change a lot over 11 billion years, growing five times bigger. They could get larger by colliding with other galaxies, but such collisions may not be the complete answer, he said.

To determine the sizes of the galaxies, the team used the Near Infrared Camera and Multi-Object Spectrometer on Hubble. Van Dokkum and his colleagues studied the galaxies in 2006 with the Gemini South Telescope Near-Infrared Spectrograph, on Cerro Pachon in the Chilean Andes.

Those observations provided the galaxies distances and showed that the stars are a half a billion to a billion years old. The most massive stars had already exploded as supernovae.

In the Hubble Deep Field, astronomers found that star-forming galaxies are small, said Marijn Franx of Leiden University, The Netherlands. However, these galaxies were also very low in mass. They weigh much less than our Milky Way, he added.

According to Franx, Our study, which surveyed a much larger area than in the Hubble Deep Field, surprisingly shows that galaxies with the same weight as our Milky Way were also very small in the past.

As to how these galaxies formed, the researchers said that it might be because of the interaction of dark matter and hydrogen gas in the nascent universe. (ANI)

Tags: , , , , , , , , , , , , , , , , , , ,

Posted in Health Science |