Young Galaxies Appear to Be Ultra-Compact

While observing galaxies in the early life of the universe, Yale University researchers discovered nine young galaxies presenting unusual high densities of stars. Although measuring only 5,000 light years in diameter, as opposed to the Milky Way which is more than 100,000 light years across, these galaxies contain amounts of matter some 200 billion times larger than our Sun.

"Seeing the compact sizes of these galaxies is a puzzle. No massive galaxy at this distance has ever been observed to be so compact, and it is not yet clear how one of these would build itself up to be the size of the galaxies we see today", said leader of the study, Pieter G. van Dokkum from Yale.

Basically these galaxies contain roughly the same number of stars as the Milky Way, only that these could fit altogether inside the galactic nucleus. "These ultra-dense galaxies, forming the building blocks of today's largest galaxies might comprise half of all galaxies of that mass at this early time", explained van Dokkum. However, over a period of 11 billion years they would suffer significant changes, mostly by expanding into space-time. "While they could get larger by colliding with other galaxies, such collisions may not be the complete answer."

The observations have been carried out with the help of NASA/ESA's Hubble Space Telescope and the Keck Observatory in Hawaii. "What we see now is that way these compact galaxies existed 11 billion years ago, when the universe was less than 3 billion years old. Only Hubble and Keck can see the sizes of these galaxies because they are very small and far away", van Dokkum said.

Previous studies of these types of galaxies have also been carried two years ago with the Gemini South Telescope Near-Infrared Spectrograph and showed that the vast majority of stars were only a billion years old, while more massive stellar bodies had already exploded into supernovae.

"In the Hubble Deep Field, astronomers found that star-forming galaxies are small. However, these galaxies were also very low in mass. They weigh much less than our Milky Way. Our study, which surveyed a much larger area than in the Hubble Deep Field, surprisingly shows that galaxies with the same weight as out Milky Way were also very small in the past. All galaxies look really different in early times, even massive ones that formed their stars early", said Marijn Franx from the Leiden University.

Van Dokkum believes that soon after the Big Bang event occurred, dark matter may have experienced uneven distribution across the universe, and large masses of hydrogen gas could have been trapped in areas with high concentrations of dark matter and started collapsing. This process could have triggered high star formation rates to create the young highly compact galaxies we see today in the early universe.

Other measurements reveal that the spin velocity around their axis is about twice as high as that observed in galaxies inside the Local Group – about 500 kilometers per second, or 1.6 million kilometer per hour. This effect is easily explainable through the fact that as galaxies become larger they find it more difficult to spin material around the nucleus.


MORE RELATED ARTICLES: Ancient Supernovae Appear to Age Slower Gravitational Radiation Full of Hot Air, Researchers Say What was Before the Universe? Peering Back into the Universe's Past 'God Particle' to be Found Soon LIGO Detector to Receive Upgrade Astronomers Look Back into the Universe's Past