Yale scientists see the birth of a massive galaxy, hidden by dust

The celestial fireworks inside the crowded core of a developing galaxy, as seen from a hypothetical planetary system.
This illustration reveals the celestial fireworks inside the crowded core of a developing galaxy, as seen from a hypothetical planetary system. Credit: NASA, Z. Levay, and G. Bacon. (Space Telescope Science Institute)

Yale University astronomers have discovered a window into the early, violent formation of the cores of the universe’s monster galaxies, obscured behind walls of dust.

After years of searching, scientists have observed one such turbulent, starbursting galactic core in the young universe using the NASA/ESA Hubble Space Telescope and a telescope from the W.M. Keck Observatory in Hawaii. The discovery offers important clues about an early phase of galaxy development, from a time just 3 billion years after the Big Bang.

The research appears in the journal Nature.

Galaxy formation theories have suggested that the universe’s heaviest galaxies develop from the inside out, forming their star-studded, central cores during early cosmic epochs. But scientists had never been able to observe this core construction until now.

“It’s a formation process that can’t happen anymore,” said Erica Nelson, a Yale graduate student who was lead author of the paper. “The early universe could make these galaxies, but the modern universe can’t. It was this hotter, more turbulent place — these were boiling cauldrons, forging stars.”

Marshaling the world’s premier telescopes, an international research team led by Yale saw this formation process underway in a massive galaxy in the early universe. They found a candidate galaxy with an infrared camera on the Hubble Space Telescope that was installed in 2009.

After finding this candidate, team members flew to Hawaii and observed it with the Near Infrared Spectrograph (NIRSPEC) on the world’s largest telescope at the Keck Observatory. The galaxy boasted the most rapidly orbiting gas clouds ever measured, definitive evidence of a massive galaxy in the midst of core formation.

Informally, the scientists began calling the galaxy “Sparky.” Using archival, far-infrared images from NASA’s Spitzer Space Telescope and the ESA/NASA Herschel Space Observatory, the team found that Sparky is producing 300 stars per year. By comparison, the Milky Way produces about 10 stars per year.

“Just like the hot oxygen-rich early Earth could produce dinosaurs, the hot, dense early universe could produce these galaxies,” said Pieter van Dokkum, chair of Yale’s Department of Astronomy. “As T-Rex was an extreme animal, these are extreme galaxies. They are tightly packed with stars and erupting with star formation.”

Sparky’s rapid gas movement was the big tip-off to core formation. Yet the same gas required to fuel star formation, along with swirling traces of metals, comes with thick dust. This dust enshrouds the galaxy, hiding it in visible light much the way the Sun can appear red and faint behind the smoke of a forest fire. Astronomers think this barely visible galaxy may be representative of a much larger population of similar objects that are even more obscured by dust.

It was only by using infrared analysis and the most powerful telescopes in existence that the Yale team could confirm Sparky’s exact nature. The galaxy formed 11 billion years ago.

“I think our discovery settles the question of whether this mode of building galaxies actually happened or not,” van Dokkum said. “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.”

In fact, Sparky may have a lot of company. “We suspect there are 100 times more and we’re just missing them,” Nelson said.

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Jim Shelton: james.shelton@yale.edu, 203-361-8332