Discovery of Ancient Galaxy Sets New Record

An international team of astronomers has, for the first time, spotted a massive, inactive galaxy from a time when the universe was only 1.65 billion years old.

This rare discovery, made using the world-class W. M. Keck Observatory on Maunakea, could change the way scientists think about the evolution of galaxies.

Artist’s impression of galaxy ZF-COSMOS-20115. The galaxy has likely blown off all the gas that caused its rapid star formation and mass growth, and rapidly turned into a compact red galaxy. CREDIT: LEONARD DOUBLET/SWINBURNE UNIVERSITY OF TECHNOLOGY.

The research was published today in the journal Nature, with Professor Karl Glazebrook, director of Swinburne’s Centre for Astrophysics and Supercomputing, as the lead author.

To characterize the faint galaxy, the discovery team used MOSFIRE, the most in-demand instrument on the 10-meter Keck I telescope.

“This observation was only possible due to the extreme sensitivity of the new MOSFIRE spectrograph,” said Glazebrook. “It is the absolute best in the world for faint near-IR spectra by a wide margin. Our team is indebted to the accomplishment of Chuck Steidel, Ian McClean and all the Keck Observatory staff for building and delivering this remarkable instrument.”

Astronomers expect most galaxies from this epoch to be low-mass minnows, busily forming stars. However, this galaxy is “a monster” and inactive.

The researchers found that within a short time period, this massive galaxy, known as ZF-COSMOS-20115, formed all of its stars (three to five times more than our Milky Way today) through an extreme star-burst event. But it stopped forming stars only a billion years after the Big Bang to become a quiescent or “red and dead” galaxy—common in our universe today, but not expected to exist at this ancient epoch.

The galaxy is also small and extremely dense, it has 300 billion stars crammed into a region of space about the same size as the distance from the sun to the nearby Orion Nebula.

Astrophysicists are still debating just how galaxies stop forming stars. Until recently, models suggested dead galaxies or “red nuggets” such as this should only exist from around three billion years after the Big Bang.

“This discovery sets a new record for the earliest massive red galaxy. It is an incredibly rare find that poses a new challenge to galaxy evolution models to accommodate the existence of such galaxies much earlier in the universe.”

To read more, go online.