Astronomers using several telescopes, including the W. M. Keck Observatory on Mauna Kea, have for the first time observed the earliest stages of a massive yet dense galaxy under construction.

Although only a fraction of the size of the Milky Way, the tiny galactic core already contains about twice as many stars as our home galaxy, packed into a region 6,000 light-years across.

By comparison, the Milky Way is about 100,000 light-years across.

"We really hadn’t seen a formation process that could create things that are this dense," said Erica Nelson of Yale University in New Haven, Conn., lead author of the study, in a statement Wednesday. "We suspect that this core-formation process is a phenomenon unique to the early universe because the early universe, as a whole, was more compact. Today, the universe is so diffuse that it cannot create such objects anymore."

The research paper appeared in the Wednesday issue of the journal Nature.

The discovery was made possible through combined observations from NASA’s Hubble and Spitzer space telescopes, the W.M. Keck Observatory and the European Space Agency’s Herschel Space Observatory, in which NASA plays an important role.

Because the galactic core is so far away, the light of the forming galaxy that is observable from Earth was actually created 11 billion years ago, just 3 billion years after the Big Bang.

Astronomers have dubbed the building site "Sparky."

In addition to determining the galaxy’s size from the Hubble images, the team dug into archival far-infrared images from Spitzer and Herschel. This allowed them to see how fast the galactic core is creating stars.

Sparky produced roughly 300 stars per year, compared to the 10 stars per year produced by our Milky Way.

"They’re very extreme environments," Nelson said. "It’s like a medieval cauldron forging stars. There’s a lot of turbulence, and it’s bubbling. If you were in there, the night sky would be bright with young stars, and there would be a lot of dust, gas, and remnants of exploding stars. To actually see this happening is fascinating."

Astronomers speculate that this prolific star birth was sparked by a torrent of gas flowing into the galaxy’s core while it formed deep inside a gravitational well of dark matter, invisible cosmic material that acts as the scaffolding of the universe for galaxy construction.

Observations indicate the galaxy had been furiously making stars for more than a billion years.

"I think our discovery settles the question of whether this mode of building galaxies actually happened or not," said astronomer Pieter van Dokkum of Yale University. "The question now is, how often did this occur? We suspect there are other galaxies like this that are even fainter in near-infrared wavelengths."