Researchers have been puzzling over massive galaxies that no longer formed stars that may have existed only three billion years after the Big Bang; a new study suggests these objects were formed by a number of "baby" galaxies.
Galaxies are collections of "stars, gas and dark matter," a University of Copenhagen - Niels Bohr Institute news release reported.
Small galaxies only contain a few million stars but larger ones can hold several hundred billion. The first stars are believed to have formed about 200 million years after the Big Bang from gases such as hydrogen and helium.
"These giant clouds of gas and dust contract and eventually the gas is so compact that the pressure heats the matter so that glowing gas balls are formed, new stars are born. The stars are collected in galaxies, the first of which are a kind of baby galaxies. As long as there is gas in the galaxy, new stars are being formed," the news release reported.
The research suggested the universe's structure was formed through collisions of baby galaxies that gradually grew more massive and spawned new stars.
"That is why it surprised us that we already when the universe was only 3 billion years old, found galaxies that were just as massive as today's large spiral galaxies and the largest elliptical galaxies, which are the giants in the local universe. Even more surprisingly, the stars in these early galaxies were squeezed into a very small area, so the size of the galaxies were three times smaller than similar mass galaxies today. This means that the density of stars was 10 times greater. Furthermore, the galaxies were already dead, so they were no longer forming new stars. It was a great mystery," Sune Toft, Dark Cosmology Centre at the Niels Bohr Institute at the University of Copenhagen, said in the news release.
These early galaxies were believed to resemble elliptical galaxies where stars move around and gas is depleted. In order for the theory of galaxy collisions to make sense there must have been some "extreme" galaxies early on in the history of the universe.
"We studied the galaxies that existed when the universe was between [one] and [two] billion years old. My theory that it must have been some galaxies with very specific properties that were part of the formation process made me focus on the special SMG galaxies, which are dominated by intense stare formation hidden under a thick blanket of dust," Toft, said.
When these "gas-rich" galaxies merged they may have driven gas into the center of the system, causing a new star to form. This "explosion" of forming stars would have caused the galaxy's center to become extremely compact and depleting the gas that could have been used to form additional stars.
"I discovered that there was a direct evolutionary link between two of the most extreme galaxy types we have in the universe - the most distant and most intense star forming galaxies which are formed shortly after the Big Bang - and the extremely compact dead galaxies we see [one to two] billion years later," Toft said.
