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Hubble find shows how dead galaxies evolve

An ancient galaxy that stopped producing new stars a very long time ago shows how dead galaxies could continue to change shape.

An artist's render of the dead galaxy (right) compared to the Milky Way galaxy. The blue areas on the Milky Way indicate star formation.
NASA, ESA, and Z. Levy (STScI)

A galaxy from the early universe has challenged what we know of how dead galaxies evolve.

Imaged by the Hubble Space Telescope, the galaxy stopped producing new stars just a few billion years after the Big Bang -- a dead galaxy. It's also an unexpected shape -- a rapidly spinning disk. This makes it the first observational evidence that some dead galaxies evolve from a disk-shaped spiral galaxy into a more three-dimensional elliptical galaxy, the more common shape for old-star and dead galaxies.

The research has been published in the journal Nature.

"This new insight may force us to rethink the whole cosmological context of how galaxies burn out early on and evolve into local elliptical-shaped galaxies," said study leader Sune Toft of the University of Copenhagen, Denmark. "Perhaps we have been blind to the fact that early 'dead' galaxies could in fact be disks, simply because we haven't been able to resolve them."

The Hubble Space Telescope was able to view this galaxy, three times the mass of the Milky Way but only half its size, in detail thanks to gravitational lensing. The Very Large Telescope provided data on the galaxy's rotational velocity, determining that it is spinning twice as fast as the Milky Way.

The team believes that merging with other galaxies is the most likely way they evolve from discs into ellipses.

"If these galaxies grow through merging with minor companions, and these minor companions come in large numbers and from all sorts of different angles onto the galaxy, this would eventually randomize the orbits of stars in the galaxies," Toft said.