A newly discovered type of young galaxy has astronomers echoing David Bowman's famous last words in the novel 2001: A Space Odyssey: "My God, it's full of stars."
While these galaxies are small enough to fit within the central hub of our own Milky Way, they each contain as many stars as larger, more mature galaxies.
The light we see from the densely packed galaxies dates to a time when the universe was relatively young, less than three billion years old.
Previously observed tiny galaxies from this time period had correspondingly small numbers of stars.
But the newfound galaxies—each only about 5,000 light-years across—weigh in at about 200 billion times the mass of the sun.
"The general trend in the nearby universe is that if you have more stars, you tend to have a bigger galaxy," said Yale University's Pieter G. van Dokkum, lead author of a new study on the galaxies.
"Apparently in these early times you could have these small galaxies with a huge number of stars."
Van Dokkum and colleagues now suspect that the small, dense systems could account for half of all the galaxies of similar mass that existed 11 billion years ago.
Young and Rich
Using the Hubble Space Telescope and the W.M. Keck Observatory on Mauna Kea, Hawaii, the team was able to measure the sizes of the distant, compact galaxies.
Further observations with the Gemini South Telescope Near-Infrared Spectrograph in Chile showed that even though the galaxies were young, they had already finished the phase of intense star formation.
"That in itself was a surprise," van Dokkum said.
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