Hubble Witnesses the Death of Giants: Ancient Galaxies Sputter Out

In the beginning, there was only darkness... Then stars began to fill the heavens, lighting our Universe. No matter what your denomination or beliefs, this is one point you likely won't dispute. Astronomers have long been fascinated with the dawn of light, and now, with the help of the Hubble Space Telescope, they believe they have determined how that beginning ended.

Experts have long believed that the Universe is about 13.8 billion years old, with our own Milky Way galaxy estimated to be about 13.2 billion years old. In the past, experts have put the now 25-year-old Hubble Space Telescope through straits to see other galaxies just over 10 billion light-years away.

This is how astronomers were able to assess 22 massive quiescent elliptical galaxies, common in the modern Universe, when they were a mere 3 billion years old - with the ancient light from these times just reaching the space telescope's lenses now.

Such colossal galaxies - also often called spheroids because of their shape - typically pack in stars 10 times as dense in the central regions as in our Milky Way, and have about 10 times the mass. Contemporary theories suggest that most spheroids finally shut down just about 10 billion years ago, at the peak of star formation in the Universe. Successor galaxies produce stars about 20 times less frequently than these pioneers.

And what Hubble was able to witness was these ancient galaxies just sputtering out. The resulting observations were recently detailed in the journal Science. (Scroll to read on...)

"Massive dead spheroids contain about half of all the stars that the Universe has produced during its entire life," Sandro Tacchella, of ETH Zurich in Switzerland and lead author of the paper, said in statement.

"We cannot claim to understand how the Universe evolved and became as we see it today unless we understand how these galaxies come to be," he added.

Using Hubble's observations in tandem with the SINFONI instrument on ESO's Very Large Telescope, Tacchella and his colleagues mapped out where exactly the galaxies were still forming new stars, if it was happening at all.

What they found was that the galaxies were dying from the core out. While the farthest outskirts still boasted new-born blue stars, their tightly-packed core remained "red and dead" - exclusively full of ancient stars and their characteristically cooling and sputtering red glow.

"The newly demonstrated inside-out nature of star formation shutdown in massive galaxies should shed light on the underlying mechanisms involved, which astronomers have long debated," added Alvio Renzini, Padova Observatory, of the Italian National Institute of Astrophysics.

With this important detail determined, experts will now turn their attention to the "why" behind these galactic deaths, investigating if it has to deal with black hole disruption, or perhaps even the introduction of gas and dust that's just too warm to be star factory fuel.

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