2/ The Milky Way is beautiful, and our home, but it’s also a bully and a cannibal. I know; it’s conflicting. But over the eons it eats other galaxies and clusters, tearing them apart and leaving the stringy undigested bits to orbit in vast streams.
3/ We know of quite a few of these. The stars are spread out over the sky but share common orbits, velocities, ages, and so on, meaning they came from the same, um, meals.

4/ This new one, called the Phoenix stream, is different. Its stars have only trace amounts of heavy elements. These elements took time for the Universe to create (in massive stars that explode), so the teeny amounts in the Phoenix stars indicate extreme age.
5/ Globular clusters (like Omega Centauri, shown here) are star cities that are pretty old, around 10 billion years. But the stars in the Phoenix stream are over *11* billion years old, older than any globular star seen!
6/ Astronomers think the Phoenix stars may be from an even older population of globular clusters than what we see today, but that population is all gone now, eaten by the Milky Way. Phoenix may be the only one of its kind that left enough remains behind to find.
7/ …or it may just be the first of its kind we’ve seen, and more are out there we haven’t found yet. That’s exciting. If there were a whole population of clusters that existed earlier than what we see now, that opens up a new window into the galaxy’s past! Very cool.
8/ We’ve known of some star streams from assimilated galaxies and clusters for a while, but new surveys, like with the Gaia satellite, have revealed many more. Gaia looks at over a BILLION stars, getting their position, motion, colors, and more. https://www.syfy.com/syfywire/how-far-away-are-the-pleiades
9/ I love this stuff. These huge surveys are showing us there’s a lot more to our galaxy than what we’ve seen before, what’s obvious. Look deep, and you find much, much more. Like what may be an entire population of objects previously unknown!
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