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Hubble has been in orbit around Earth for more than 30 years now, and it gave scientists
a bit of a scare at the beginning of March when it encountered some problems with its
onboard computer.
Thankfully, the mission team has since successfully recovered Hubble, and everything is functioning
as normal.
Hubble’s mission is due to continue for many years yet, scientists expect Hubble to
continue on until the late 2030s.
So, what are some of the incredible discoveries it has made so far?
Well today, I wanted to focus on one of the most beautiful aspects of space.
A wide angled uninterrupted view of the sky reveals something quite remarkable.
There are literally hundreds of nebulae spread out across our view, the birthing place from
which all stars come from.
But the term nebula covers a lot of different types of interstellar clouds, each with unique
and beautiful characteristics.
I’m Alex McColgan, and you’re watching Astrum, and in this episode of the Hubble
Images series, we are going to explore a variety of spectacular nebulae that Hubble has examined,
and I’ll explain to you what it is that you’re looking at.
The first thing to quickly explain before jumping into the Hubble images is that all
nebulae are part of something called the Interstellar Medium.
The Interstellar Medium is the gas and dust that is unevenly dispersed around our galaxy.
This is what the Interstellar Medium looks like from our viewpoint on Earth.
Some parts of it only have 1 particle per cubic centimetre, as close to a true vacuum
as you can get.
The densest regions, which are like the nebulae I’m about to show you, can have millions
of particles per cubic centimetre, which is still incredibly dispersed if you consider
our atmosphere has 10 quintillion particles per cubic centimetre at sea level.
However, over the many light years these nebulae stretch across, this mass really adds up.
Let’s look at our first example and I’ll show you what I mean.
Number 61, The Circinus molecular cloud.
The most basic type of nebula is an inert, cold, and dark nebula, also known as a molecular
cloud.
They are named like this because they mainly consist of the molecule H2.
In this state, they don’t do much, and we can only really see them because they block
the light behind them.
However, molecular clouds are some of the most densely packed nebulae out there, with
millions of particles per cubic centimetre.
They sit in space for millions of years, prevented from collapsing in on themselves by their
own internal pressure.
That is, until an external force comes along and bumps the cloud.
This force could be from a supernova shockwave, or from density waves in the galaxy.
In any case, this nudge overcomes the internal pressure of the cloud, causing it to start
collapsing in on itself from its own gravity.
And the result is what you see tucked into the centre of the Circinus molecular cloud,
a star being born.
This entire cloud has 250000 times the mass of our Sun, meaning if the whole thing collapses,
there’s going to be a lot of stars in this spot in several million years.
If we zoom in on the star that has already formed, we can see some interesting phenomena.
The bright nebula surrounding the star is still part of the Circinus molecular cloud,
it has just been lit up from the light of the young star.
This region is known as a reflection nebula, a nebula that simply reflects the light shining
on it.
You can also just about see a protostellar jet shooting away from the star, the leftovers
from the gas and dust it absorbed from the molecular cloud.
It’s a different colour because it is really hot, having come from the star itself.
Let’s move on to Number 62, NGC 2014 and NGC 2020.
This breath-taking image is a great example of one of the most famous types of nebula,
known as a HII region.
HII regions are basically what happens to a molecular cloud once star formation has
really gotten going.
The biggest difference between a molecular cloud and an HII region is that an HII region
produces its own light, the particles within it have been ionised by the solar wind and
UV light from the young, hot stars shining within them.
HII regions also tend to be a little less dense than molecular clouds, containing only
hundreds to thousands of particles per cubic centimetre.
In this particular image, you have what appears to be two separate nebulae side by side, but
actually they are part of the same cloud, it’s just that only two parts of the cloud
have been carved out and ionised so far.
The different colours come from the differences in ionised materials, in the red section,
the ionised gas is hydrogen, in the blue section, the ionised gas is oxygen.
This difference is due to the way these two regions came to be.
In the red section you’ll see hundreds to thousands of stars, each more than 10 times
the mass of our Sun.
It’s UV radiation from these stars that is ionising the hydrogen around them.
Stellar winds from the stars can be seen carving out the nebula.
Here, the nebula is dense, and so is more resistant to the stellar wind.
Here, however, the nebula is less dense, and the stellar wind has carved bubble shapes
into it, reminiscent of coral.
The blue region, unlike the red region, has been shaped by a single, massive star, known
as a Wolf-Rayet star.
This type of star is the hottest and most luminous star out there, this one being 200,000
times more luminous than our Sun.
Because it is so hot and luminous, its expected lifespan is very short, only a few million
years.
And over the course of that time, it is shedding a lot of its mass in the form of powerful
stellar wind.
It’s this wind which has interacted with the oxygen specifically, increasing its temperature
to over 11,000°C, which is way hotter than the ionised hydrogen also in the nebula.
You can see a small section of the red nebula also has some heated oxygen towards the centre,
which beautifully looks like water lapping up against a beach, and to a lesser extent,
there’s some blue over here too.
Overall, a stunning image from Hubble.
Number 63, and a different type of nebula again with NGC 7027, or the Jewel Bug Nebula.
The previous two types of nebula we looked at are closely related, unlike this beautiful
type of nebula which originates from something completely different.
While molecular clouds and HII regions span hundreds to thousands of light years, a planetary
nebula like this one is only a couple of light years across at most.
And while molecular clouds and HII regions contain enough mass to produce thousands of
stars, planetary nebulae barely contain enough for one.
This is because this nebula is the result of an intermediate mass star on its last legs,
the star at the centre of this nebula is coughing and spluttering its outer shell into space
before it contracts into a white dwarf star.
Incredibly, because Hubble’s mission has been going on for so long, it means we can
sometimes see a tiny part of a planetary nebula’s evolution.
Here’s number 64, the Stingray nebula.
This planetary nebula has changed drastically between 1996 and 2016.
Just look how it has dimmed over only 20 years.
This is very unusual.
Because of the vast time scales involved for us humans, usually we only see limited movement
over such a time frame.
For example, number 65, the Cat’s Eye nebula.
This planetary nebula has barely shifted at all over a similar time scale.
It’s not too hard to see why this nebula has the name it does, and it’s really quite
beautiful, both up close and more zoomed out where you can see gas and dust that has been
previously ejected.
Planetary nebulae are somewhat similar to HII regions in that they are both emission
nebulae, they produce their own light through ionisation of the gas particles from stellar
winds.
Let’s have a look at another one.
Number 66, NGC 7293 or the Helix Nebula.
What a piece of art this is.
The fascinating thing about planetary nebulae is that while some share similar characteristics,
no planetary nebula is ever identical, and each produces its own unique fireworks display.
And we are lucky to have witnessed these ones, because as planetary nebulae expand, disperse
and cool, they will be lost from view only tens of thousands of years after the event,
leaving the tiny white dwarf star behind.
Which means the ones we can see now happened very recently, astronomically speaking.
And because they are so small compared to the other nebula types we’ve seen so far;
they can only be spotted in our local galactic neighbourhood.
The Helix Nebula is especially close to us, being the size of half a full moon in our
sky, which allows us to peer inside and see its remarkable details.
I think what’s so incredible about this image is seeing how the stellar wind from
just this one star is blasting away at the dust halo which had been ejected away from
the star before the planetary nebula formed, just like the halo we saw in the Cat’s Eye
Nebula.
With the Helix Nebula, the expansion of the planetary nebula has now caught up with the
halo and is carving it away.
This is a mind-blowing image of space and it’s probably one of my personal favourites.
There are so many more beautiful examples of planetary nebulae that I could show you,
but let’s finish this episode on number 67, The Hourglass Nebula.
This nebula is pretty far away at 8000 light years so we can’t see it in the same detail
as the Helix Nebula.
However, its shape, colour and this little beady eye in the centre are truly phenomenal.
Sometimes, if the planetary nebula originated from a tightly orbiting binary star system,
what you’ll get is a two lobed nebula.
This could be the case for this one, and you can see the star or stars towards the centre
here.
No, this isn’t the reflection from the camera flash that pareidolia would have you believe!
Although we are long overdue for an upgrade to Hubble, it really is still a feat of engineering,
and it’s been really interesting to me to learn about the telescope itself.
MagellanTV has an amazing documentary about the behind of scenes of Hubble, how the mission
team operates it and some of the obstacles it has to overcome, for instance, the South
Atlantic Anomaly which is really quite fascinating and something I didn’t know about before.
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Thanks for watching!
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Be sure to check the cards in the top right of this video for a lot more about nebulae
and how they work, it’s really a fascinating topic.
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All the best and see you next time.