Space can be beautiful.
You have flawless elliptical galaxies, with no traces of dust bands blocking the view
of their stunning shape.
You have grand galaxies with spiral arms that wrap around the entire galaxy with a surprising
level of symmetricity.
And then, you have the ARP catalogue, or the Atlas of Peculiar galaxies.
These are galaxies which laugh in the face of order, galaxies which are often going through
a very tumultuous time in their existence.
And they are fantastic in their own right, each with a story to tell.
I’m Alex McColgan, and you’re watching Astrum, and in this Hubble episode, we will
go through some of the most peculiar galaxies that Hubble has ever seen, and I’ll try
and explain what it is you are looking at.
43.
Arp 116, M 60.
At first glance, this galaxy doesn’t look so unusual.
It seems like a standard elliptical galaxy, a massive galaxy which has already used up
most of its dust and gas in creating stars which gives it this smooth appearance.
It can be found about 57 million ly away, and has one of the biggest black holes ever
discovered near its centre, at roughly 4.5 billion solar masses.
But this isn’t particularly peculiar so far.
But zooming out a bit reveals something very unusual, M60 is right next to another, very
different looking spiral galaxy called NGC 4647.
From our viewpoint, it looks like the galaxies should be interacting with one another, but
there aren’t any immediate signs of this.
This is really unusual, to see two galaxies so close but without any warping of their
shape.
As it turns out, they are not side by side, but rather one is in front of the other.
There’s one other really unique thing in this image, another galaxy you probably haven’t
noticed.
This tiny little galaxy here is known as M60-UCD1.
It is the most densely packed galaxy that we know of, being only 300 ly across and having
200,000,000 solar masses contained within it.
Towards the centre of this tiny galaxy, stars are so densely packed, it makes the density
of stars about 15,000 times greater than found in Earth's neighbourhood in the Milky Way,
meaning that the stars are about 25 times closer together.
An X-Ray view of the surrounding area from the Chandra telescope reveals all the black
holes and neutron stars found in M 60, and as you can see this tiny galaxy also has an
x-ray source, indicating there is also a black hole to be found at the centre.
Scientists believe this is a black hole with roughly 10 mil solar masses, which would make
is a just a bit bigger than the black hole found at the centre of our Milky Way galaxy.
If this is the case, it is thought that this galaxy used to be much bigger, but most of
its mass was stripped away, leaving just this dense cluster of stars found near the centre.
44.
Arp 147, IC 298.
You don’t have to look too closely at this image to determine that this is a very weird
looking galaxy.
It is in fact a pair of galaxies that have collided, found roughly 440 mil ly away.
This is what the previous galaxies could end up looking like if ever they collide, because
the left galaxy is an elliptical galaxy and the one on the right is a spiral galaxy.
The collision, estimated to have happened 40 mil years ago caused the spiral galaxy
to undergo extreme star formation, seen in the bright blue regions.
The most active time of star formation, or starburst, was 15 mil years ago, and would
have produced the most massive types of stars.
But due to these stars being short lived, lasting only 10s of million of years, most
of the biggest ones have already died as exploding supernova and become either neutron stars
or black holes.
This reddish part of the ring appears to be the original nucleus of the galaxy, now just
a segment of the ring.
Due to elliptical galaxies having exhausted most of their supply of dust and gas, star
formation isn’t nearly as prevalent in this galaxy.
What you can see though is the effect of the tidal forces causing a ripple or shockwave
through the galaxy, which you can see as the stars have clumped into rings.
45.
Arp 77, NGC 1097.
Another galaxy with a smaller galaxy tucked away inside it is NGC 1097.
Unfortunately, the Hubble image cuts the smaller galaxy out, but ESO’s VLT has also had a
look at the galaxies, in which you can see its smaller neighbour, NGC 1097a, a small
elliptical galaxy that is in orbit around the bigger galaxy.
NGC 1097 itself looks quite like a giant eyeball to me, with its pupil surrounded by
a bright iris.
Zooming in on the iris, we can see that it is a ring rich in star forming regions.
Each of the bright blobs are thought to be hot bubbles of hydrogen in which stars are
forming.
Viewing different wavelengths of light shows that some dust from the rings is also being
sucked in towards the super massive black hole found in the galaxy’s centre.
But this isn’t the most peculiar thing about NGC 1097, zooming all the way out reveals
four jets emanating from the core of the galaxy in an X shape.
Due to the lack of hydrogen gas found in these jets, scientists instead believe that they
are the remains of a small galaxy that NGC 1097 cannibalised!
46.
Arp 142, NGC 2936, NGC 2937.
Here is another galaxy merger that kind of looks like a penguin and an egg.
When viewed like this, this image might seem serene almost, but in fact the bigger spiral
galaxy has taken a beating from this merger.
This long section here is where one of the spiral arms of the galaxy has been ripped
away by the elliptical galaxy, which doesn’t look like its too fazed by this collision,
other than the fact it looks quite oblong in shape.
Again, the blue regions along the edges here contain starburst, and this 3D view shows
that these dust lanes are probably becoming detached from the galaxy too.
These galaxies are found roughly 350 mil ly away.
47.
Arp 210, NGC 1569.
Now I don’t think you’ve seen a galaxy quite like this one.
Well that’s because this tiny galaxy, no bigger than the Large Magellanic Cloud orbiting
our Milky Way galaxy, is pretty much is just one giant nebula.
This galaxy is almost the total opposite of an elliptical galaxy, as it is rich in gas
and dust that has not yet formed stars.
NGC 1569 is found near the Maffei group of galaxies, and due to its close proximity to
these much bigger companions, the gas and dust within it has recently been compressed,
causing rapid starburst at a rate 100 times faster than anything observed in our own Milky
Way!
Towards the centre are densely packed, massive stars which have blasted away the red dust
and gas towards the outskirts of the galaxy through solar wind and supernova explosions,
leaving behind huge star clusters.
The small white stars found in the halo of the galaxy are older stars which have been
around for much longer.
We can have such a detailed look at this galaxy because although it is small, no bigger than
6000ly across, it is also reasonably close to us at 11 mil ly away.
48.
Arp 272, NGC 6050 and IC 1179.
We’ll finish with one more galaxy merger seen from a rather interesting angle.
These two galaxies are roughly the same size and are just astronomical moments away from
impacting each other.
There’s also a third galaxy found just above them, which is also in on the action.
The reason for seeing three galaxies merging at the same time could be due to the fact
this happening in the Hercules supercluster, roughly 500 mil ly away, which is one of the
biggest filamentary structures of galaxies that we know about in the universe.
You see, the observable universe as far as we can tell kind of looks like a giant web,
where galaxies band together to form these filaments, which form the boundaries between
large voids in the universe.
This is what the universe up to 500 mil ly from us looks like, and even in this space
you can see this banding of galaxies.
And just because some of you have asked about this in the past, this is where Boötes void
is, which is one of the biggest voids of galaxies that we know about.
Thanks for watching!
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Well, I hope some of these images have impressed you as much as they impressed me.
If you are new to the channel and want to see more Hubble images, check out the playlist
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All the best, and see you next time.