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Let's talk about fossils, not the dinosaur

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remnants here on Earth,
but the galactic kind.

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Scientists recently found one
that's helping them understand galactic

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evolution.

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Just 13 million
light years from here is a galaxy

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called NGC 4945.

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At its center is a supermassive black
hole.

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It's surrounded by both a disk of gas
emitting a lot of light

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and a bunch of dust
blocking much of that light.

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The galaxy is also in a phase of evolution
called starburst,

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where a lot of stars are being born near
its center.

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Recently using X-rays,

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ESA’s XMM-Newton telescope spotted

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a cloud of cold gas in NGC 4945.

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The gas expands light years
beyond the central part of the galaxy

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and pokes out into intergalactic space.

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NASA's Chandra X-ray Observatory
helped study it, too,

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by looking at individual,
bright sources of X-rays within that

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cloud.

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Scientists think that the area of cold gas
is a fossil of an eruption

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from a black hole
that happened about 5 million years ago.

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That eruption

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may have caused the galaxy's burst of star

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formation.

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Studying galactic change is hard

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because it happens over
such long timescales.

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But by looking at lots of examples,
scientists can piece together

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how galaxies like NGC 4945

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and our Milky Way evolve.