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Astronomers have announced 29 newly discovered ultracompact galaxies in five billion light years from Earth.
The galaxies are so called because of their huge mass. They contain several times more stars than the Milky Way, packed in a much smaller volume. This makes them extremely bright but also rare.
Using data from the nearby Galaxy and Mass Assembly (GAMA) research, astronomers led by Fernando Buitrago of the Institute of Astrophysics and Space Sciences of Portugal have identified up to 29 of the galaxies between two and five billion light-years away.
The GAMA data were complemented with observations made by the VLT Survey Telescope of the European Southern Observatory in Chile. The combined results were published in the journal Astronomy and Astrophysics.
"They are so rare that we need about a volume of nearly 500 million light-years to find a single one of them," says co-author Ignacio Ferreras.
Of the 29, seven of the oldest are of particular interest. The group has remained virtually untouched by others since its formation more than 10 billion years ago. Having existed without drastic external influences, its members reveal what galaxies were like in the early ages of the universe.
Usually, astronomers would need to look away to gain such insights, but these relics are, galactically speaking, in the local neighborhood. This proximity offers a range of opportunities for Buitrago and his team.
"When you study very small objects and study them in the distant universe, it is very difficult to say anything about them," he explains.
"As this sample of galaxies we studied is in the near universe and relatively close to us, even though they are truly small, we have a better chance of probing them."
The findings challenge some of the hypotheses of galaxy formation and evolution. It was thought that massive and ultra-compact galaxies could only exist in dense clusters of galaxies, where complex gravitational forces and high galactic velocities prevented them from interacting significantly or merging with others.
"The surprise came when we realized that not all the galaxies in our sample live in such systems," says Buitrago.
"We find them in a variety of environments, and for those living in dense neighborhoods, this is very difficult to explain."
With its relative proximity and properties similar to the time-capsule, the newly discovered batch will provide an unprecedented opportunity for astronomers to understand galaxies of all sizes, not just the ultra-compact mass type, according to Buitrago.
"Massive galaxies evolve rapidly compared to other galaxies in the universe," he says. "Understanding the properties of the most massive galaxies, we could understand the ultimate fate of all other galaxies, including our own Milky Way."
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