Tiny Galactic Building Blocks Spotted

A view of some of the dimmest, smallest and most compact galaxies from Hubble's Ultra Deep Field image. Some of their structures hint at the first signs of galaxy fusion, just 1 billion years after the Big Bang. Credit: NASA/ESA/N. Pirzkal

Astronomers have found nine of the faintest, tiniest and most compact galaxies ever seen.

The little objects are hundreds to thousands of times smaller and vastly younger than our Milky Way, lending support to a "building block" theory in which hundreds of the tiny galaxies merge together and form larger bodies of stars.

"These are among the lowest mass galaxies ever directly observed in the early universe," said Nor Pirzkal of the Space Telescope Science Institute in Baltimore, Md.

Pirzkal said their petite mass, observed by the Hubble Space Telescope and confirmed by the Spitzer Space Telescope, shows these galaxies are some of the smallest building blocks of the universe, aside from stars themselves.

The two telescopes saw light emitted from the galaxies only 1 billion years after the theoretical Big Bang, giving a rare glimpse into the past. Sangeeta Malhotra, an astronomer at Arizona State University who helped make the discovery, said the absence of infrared light in the sensitive Spitzer images showed the stars are first-generation and only a few million years old.

"These are truly young galaxies without an earlier generation of stars," Malhotra said.

Hubble detected hot blue stars within the nine galaxies, indicating that the youthful stars are in the process of turning hydrogen and helium into heavier elements like carbon, oxygen and silicon necessary for planet-building--and life. The astronomers speculated, however, that such stars probably haven't begun to "pollute" space with the crucial elements forging within their cores.

The development of three of the galaxies appears to be slightly disrupted; rather than taking on a rounded-blob shape typical of the youngest galaxies, they're stretched into tadpole-like forms. Astronomers think it may signal their first fusion with neighboring galaxies to form larger, cohesive structures.

The galaxies were observed in the Hubble Ultra Deep Field (HUDF) image with Hubble's Advanced Camera for Surveys and the Near Infrared Camera and Multi-Object Spectrometer. Observations were also done with Spitzer's Infrared Array Camera and the European Southern Observatory's Infrared Spectrometer and Array Camera.