Hot Times in NGC 1569

NGC 1569
NGC 1569

We usually think of space as this serene place where stars shine and planets bob around and galaxies are out there. Except, of course, it’s not quite true. Depends on where you’re looking to and from. Take the the nearby dwarf galaxy NGC 1569 as an example. It’s a close (meaning it’s about 7 million light-years away) starburst galaxy — a hotbed of vigorous star birth that blows huge bubbles of gas. The galaxy’s “star factories” are also manufacturing brilliant blue star clusters.

As it turns out, NGC 1569 had a sudden onset of star birth about 25 million years ago. Lots of new stars were born and then things quieted down a bit about the time the very earliest human ancestors appeared on Earth.

This new image from the Hubble Space Telescope shows the bubble structures being sculpted by galactic super-winds and outflows. These are the result of supernova explosions that are themselves linked to massive episode of star birth. That makes sense when you think about it: the stars are born, and then some millions of years later they start to die. If they’re massive stars, they live short lives (well, short compared to longer-lived stars like the Sun) and die spectacularly as supernovae.

This whole episode of star formation and star death, intertwined in a single spectacular image, brings us to one of the still unresolved mysteries in astronomy: how and when galaxies formed and how they evolved. Most of today’s galaxies (including the Milky Way) seem to have formed quickly very early on in the history of the universe. Galactic births very likely involved one or more galaxy collisions and/or episodes of strongly enhanced star formation activity (the so-called starbursts).

While any galaxies that are actually forming are too far away for detailed studies of their stellar populations even with Hubble, their local counterparts, nearby starburst and colliding galaxies, are far easier targets. NGC 1569 is a particularly suitable example, being one of the closest starburst galaxies. It harbors two very prominent young, massive clusters plus a large number of smaller star clusters. The two young massive clusters match the globular star clusters we find in our own Milky Way galaxy, while the smaller ones are comparable with the less massive open clusters around us.

The majority of clusters in NGC 1569 seem to have been produced in an energetic starburst that started around 25 million years ago and lasted for about 20 million years. The bubble-like structures that resulted are made of hydrogen gas. It glows when hit by the fierce winds and radiation from hot young stars and is racked by supernovae shocks. The first supernovae blew up when the most massive stars reached the end of their lifetimes roughly 20-25 million years ago. The environment in NGC 1569 is still turbulent and the supernovae may not only deliver the gaseous raw material needed for the formation of further stars and star clusters, but also actually trigger their birth in the tortured swirls of gas.

So, in one image you get starbirth, stardeath, galaxy evolution, and something a little more: another great image to learn from, thanks to the Hubble Space Telescope.

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