Astronomers had been puzzled why none of these objects, dubbed "red nugget" galaxies, were seen nearby our own Milky Way galaxy, and wondered if they had disappeared over time.
New analysis of data from the Sloan Digital Sky Survey conducted by a telescope in New Mexico showed they hadn't disappeared completely, but rather were hiding in plain sight, concealed within the data of previous astronomical surveys, they said.
"Red nugget" galaxies are so small that they appear like stars in photographs from ground-based telescopes, the researcher said, but their spectra give away their true nature.
"Looking for 'red nuggets' in the Sloan Digital Sky Survey was like panning a riverbed, washing away silt and mud to uncover bits of gold," Ivana Damjanov of the Harvard-Smithsonian Center for Astrophysics said.
By sifting through the Sloan data, the team identified more than 600 "red nugget" candidates located at distances of 2.5 billion to 5.7 billion light-years from Earth.
The most massive "red nuggets" weigh up to 10 times more than the Milky Way but are up to 10 times smaller than our galaxy.
They could represent a missing link between distant "red nuggets" and nearby elliptical galaxies, the researchers said, and may help explain how small, compact galaxies age over time and become "seeds" for the monster elliptical galaxies seen throughout the universe today.
"We think there are more of these red nuggets, or compact galaxies, hidden in the universe, waiting to be discovered," study co-author Ho Seong Hwang said.