The universe can be an amazing, terrifying, and incredibly weird place.
We’ve talked about planets so strange they probably shouldn’t exist, but that’s just
the tip of the iceberg in a universe with hundreds of billions of galaxies.
Over the years, astronomers have discovered a lot of galaxies that they never would have
expected to find — huge collections of stars that formed in ways we still can’t explain,
or because of a rare coincidence.
About 600 million light years away, for example, is a place so odd that for decades astronomers
weren’t even sure whether it was a galaxy.
Today we call it Hoag’s Object after its discoverer, Art Hoag, who discovered it in
1950.
It’s a striking example of a rare type of galaxy known as a ring galaxy.
The middle of a ring galaxy is pretty normal-looking.
But it’s surrounded by a huge loop of stars, dust, and gas.
And Hoag’s Object is especially remarkable because of the contrast between the galaxy
and the ring.
The inner clump shines brightly with a ton of older, redder stars, while the outer ring
is mainly made up of younger, bluer ones.
And the area between the center and the loop seems almost totally empty!
Astronomers have a few ideas about how ring galaxies might form, but Hoag’s Object doesn’t
line up neatly with any of them.
Some ring galaxies are thought to form when a smaller galaxy strikes a larger one and
the resulting shockwave pushes material out to form the ring.
But if that happened to Hoag’s Object, where’s the second galaxy?
You’d expect it to be somewhere nearby.
Ring galaxies might also form when one galaxy passes close enough to another for its gravity
to strip away some of the stars.
But that would be a messy process and probably wouldn’t result in such a neat, confined
ring.
So even after decades of studying it, astronomers really don’t know how Hoag’s Object could
have formed.
Now let’s travel back more than ten and a half billion years, to a galaxy named BX442.
It’s the earliest known grand design spiral galaxy, a category of galaxies identified
by their long, graceful spiral arms.
These days about 10% of galaxies have this sweeping appearance, but the farther back
you go, the less often they appear.
That’s probably because in the past, galaxies were closer together, which led to a lot more
spiral-destroying collisions.
Older grand design spiral galaxies are so rare that in a sample of more than 300 ancient
galaxies examined in one study, BX442 was the only one to display any sort of spiral
structure.
And astronomers think they might know why.
There’s a nearby dwarf galaxy that might have passed close to BX442, and this smaller
galaxy’s gravity could have helped with the formation of spiral arms.
In that case, BX442’s beauty might have lasted only a hundred million years.
So this galaxy only existed because that dwarf galaxy happened to be passing by.
And we’re only seeing it because we happened to catch it at the right time.
Another strange galaxy is even older — it existed just 700 million years after the Big
Bang.
That’s only a couple hundred million years after the earliest known galaxies.
But A1689-zD1 looks downright old.
That’s because it’s full of something that’s thought to have been rare in the
early Universe: dust.
Interstellar dust contains elements heavier than hydrogen and helium, and those heavier
elements weren’t around right after the Big Bang.
Instead, they were produced by supernovas, the explosive deaths of giant stars.
When a star explodes, it turns lighter elements into heavier ones and spreads them through
space.
Over time, this builds up large clouds of interstellar dust.
To create the amount of dust seen in this galaxy, there must have been a lot of star
formation and star death going on.
And the same stuff that makes up dust also forms the building blocks for planets, which
means this galaxy might have had more developed star systems, too.
So it was really mature for such a young galaxy.
Like Hoag’s Object and BX442, this ancient galaxy is one of the most surprising galaxies
astronomers have ever discovered.
And we’ve only seen a tiny fraction of all the galaxies out there.
So who knows what else we’ll find?
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