Let's talk about fossils, not the dinosaur
remnants here on Earth, but the galactic kind.
Scientists recently found one that's helping them understand galactic
evolution.
Just 13 million light years from here is a galaxy
called NGC 4945.
At its center is a supermassive black hole.
It's surrounded by both a disk of gas emitting a lot of light
and a bunch of dust blocking much of that light.
The galaxy is also in a phase of evolution called starburst,
where a lot of stars are being born near its center.
Recently using X-rays,
ESA’s XMM-Newton telescope spotted
a cloud of cold gas in NGC 4945.
The gas expands light years beyond the central part of the galaxy
and pokes out into intergalactic space.
NASA's Chandra X-ray Observatory helped study it, too,
by looking at individual, bright sources of X-rays within that
cloud.
Scientists think that the area of cold gas is a fossil of an eruption
from a black hole that happened about 5 million years ago.
That eruption
may have caused the galaxy's burst of star
formation.
Studying galactic change is hard
because it happens over such long timescales.
But by looking at lots of examples, scientists can piece together
how galaxies like NGC 4945
and our Milky Way evolve.