Stone-dead galaxy helping astronomers understand galactic evolution

Dead Galaxy vs Milky Way
MACS2129-1, right, The Milky Way, left.

A team of astronomers has discovered what they claim is a stone-dead galaxy some 10 billion light-years from Earth using the Hubble space telescope and gravitational lensing.

Researchers say the discover is remarkable for it strongly contradicts prevalent astrophysical theory regarding the formation of elliptical-shaped galaxies shortly after the Big Bang 13.7 billion years ago. The newly discovered galaxy has been named MACS2129-1; is three times heavier than the Milky Way, but only half the size. This effectively makes MACS2129-1 an extremely compact galaxy.

Galaxies are stellar systems in space and astronomers distinguish between two main types: disk-shaped spiral galaxies, e.g. the Milky Way, and elliptical-shaped galaxies. One of the distinct differences between the two main types being that while the disk-shaped galaxies still make new stars by transforming gas, the elliptical-shaped stopped doing this long ago – which is why the latter are deemed ‘dead’.

Furthermore the stellar motions differs markedly between the two main types:  In the Milky Way and in other disk-shaped galaxies stars rotate with a regularity that is predictable – whereas stellar motions in elliptic-shaped galaxies can be seen as rather more chaotic.

Why elliptic-shaped galaxies stopped producing new stars way back in the history of the universe has long puzzled astrophysicists. The prevalent theory speculates that collisions between galaxies in some cases may have provoked a sort of over-production in certain galaxies – because all available gas was compressed in their center and transformed to new stars. Whereupon these elliptical-shaped galaxies ceased stellar production – and ‘died’.

With MACS2129-1, however, things are different. Albeit it can be said with certainty that the galaxy is not producing new stars – and therefore can safely be considered stone-dead – its existing stars are nevertheless distributed in a rotating disc. Exactly as can be seen in the Milky Way!

Observation of the galaxy was made possible because the stone-dead galaxy was positioned behind a foreground cluster of other galaxies – a cluster which functioned as a ‘natural lens’ by amplifying as well as enlarging the image of MACS2129-1. And that made it possible for the researchers via Hubble and VLT to study in detail the distribution of stars in the galaxy as well as the patterns of stellar rotation.


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