Monday, 18 June 2018

NGC6567: a planetary in full expansion

Young planetary nebulae are not always easy to find because of their tiny size they usually resemble an ordinary star at low telescope power. Yet, with the aid of a nebula filter - UHC or OIII, which blocks all light frequencies apart from those predominantly radiated by these nebulae - they easily stand out as a bright and somewhat fat star against the dark background. If you then increase magnification to as much as your telescope or sky conditions allow, you'll often be surprised. Due to their high surface brightness they let you use extreme high power and not seldom show some extraordinary detail.

Take this little bugger, for example. NGC6567 lies some 4,000 light-years away from us in the direction of the marvelous Sagittarius Stellar Cloud. It gets lost somewhat in the extremely rich star field of the centre of our galaxy, but with the aforementioned method you'll still be able to find it without too many difficulties. At 507x it becomes obvious that this is a planetary nebula and not a star. What's more, its bright inner ring, an enormous bubble of ionised gas that the dying star's expelled some 4,000 years ago, just leapt out at me. This bright bubble's currently expanding at 13km/s, which is not exceptionally high. Yet without any doubt this nebula will become much more spectacular in the course of the following millennia, when it will expand further.

Sunday, 10 June 2018

The Eskimo... again...

In one of my first posts I talked about NGC2392, otherwise known as the Eskimo Nebula for obvious reasons. It does look like a head wrapped in a parka hood, doesn't it? 

This winter, during a very clear (but teeth-chattering cold) night I finally pointed the binoscope at it and pushed power to 507x. There are these moments when an 18" binoscope not just performs on par with high-quality photographs but even outperforms them. This was one of these moments. 

Astronomical sketching is a very subjective form of art and often artistic creativity tends to take the upper hand on true scientific observation. It's a delicate balance because we sketchers want to show the viewer every detail we (think we) have spotted. Observation through a telescope, however, usually resides at the very edge of what a human eye can possibly capture; staring at a faint object for minutes if not hours, direct vision, averted vision, trying to avoid any external interference. Sometimes it gets so bad that the whole image starts dancing in front of our eyes, especially with one-eyed viewing, and we get overwhelmed by fatigue. Therefore it's generally so hard to tell whether certain details were really observed or merely intuitively suggested. 

Then there's the question of how you want to represent these faintest of details. If you draw them clearly, the image easily gets "overdone" and albeit artistically pleasing and massively impressive, you can't really state that that's exactly how you've seen the object at the eyepiece. Any viewer who'd look through a telescope after being wowed by such a drawing would be seriously disappointed. 

Personally, I prefer to draw everything as realistically as possible, even if I have to make some details all but invisible. This may perhaps result in less impressive sketches and I've already read a lot of criticism on my work on-line, like someone claiming that he can see a lot more with his 9,25" SCT. Well, if that's the case, I'm very happy for him. My aim is to give the viewer (hopefully) the same challenge as I had behind the eyepieces. "Can you see it or not?" I don't care if my sketches don't look as fancy as some others. 

Astronomical sketching is not a competition.  

Yet, in the particular case of the Eskimo, I didn't have to hide any details at all because this is exactly how it appeared at first glance.

Friday, 25 May 2018

NGC3242: Jupiter's Ghost

Low on the horizon, for northern observers, during the early spring months... in an otherwise seemingly empty part of the sky you may stumble upon this big and bright planetary nebula. It's popular name "Jupiter's Ghost" refers to its similar apparent size and shape compared to the biggest planet of our solar system. In reality this nebula is some two light-years across and is still in full expansion. It merely appears the size of Jupiter because it is 1,400 light-years away.

The bright inner halo, the central star's dying breath, was blown into space some 1,500 years ago and is now rapidly catching up with the large outer shell which gradually built up during the final phase of the star's life. It's central star of 11th magnitude was not that easy to see, although it's radiating at over 150,000°C and lighting up the gas bubble around it. The gas is heated up to the extent that it begins to ionise and emit a bluish-green light of its own. Actually, we're catching this nebula right at its brightest phase. Within the next couple of thousand years it will expand further, fade and eventually dissolve into space.

Thursday, 17 May 2018

NGC5005: Black holes lead to star formation?

Yes, I know, it's a bit of a strange title for this post. Let's have a close look at NGC5005, a galaxy that's not in our immediate vicinity (estimates vary greatly from 45 to 113 million light-years, with an average of 65). It's a fairly bright galaxy in Canes Venatici, the hunting dogs, which can be seen quite easily with a modest telescope. 

Through the binos at 285x, it revealed a wonderful amount of detail, such as the darker arc on the left. But what we're really interested in, is its nucleus. Spectroscopic analysis revealed that the heart of this galaxy contains a lot of non or weakly ionised atoms, such as O, O+, N+, and S+. Scientists classify galaxies with such a cloud of weak ions in their core LINERs, which stands for "Low-Ionisation Nuclear Emission". This is nothing unusual and as it appears up to a third of all galaxies could fall under this category. The question however, is what causes this enormous cloud, which may swirl inward up to 750km/s! Scientists are still heavily debating on that, but significant x-ray emissions in the case of NGC5005 seem to confirm a super-massive black hole in its centre. Another observation that we make, is that this ion cloud produces some serious star formation. Usually not a lot of stars are formed in the nucleus of a galaxy, which therefore contains an older star population, and most starburst activity is generally concentrated in billowing spiral arms. 

So may we conclude that a black hole can be so powerful as to cloak itself with a cloud of ionised gas in which thousands of new stars are born? 

Thursday, 3 May 2018

Frosty Leo... again

I've already written about this highly unusual planetary nebula in construction two years ago and will repeat most of this post here, to give you some background information on IRAS 09371 + 1212, or in other words "Frosty Leo". 

When I made my first observation, I was unfortunately limited to 200x, which is far from sufficient if you want to see some detail in this tiny puff of mostly water crystals. So here's my recent observation with the binoscope and... yes... at 507x details were abundant!

Nature is ruthless. It gives life and make stars sparkle so brightly in our sky that uncountable poets have dedicated their most beautiful work to them. But unfortunately, all beauty must fade and everything that has a beginning also has an end. Even so the seemingly perpetual stars which eventually have to die too. I've repeatedly written about dying stars, either the ones that go fairly quietly through the formation of a planetary nebula, or the ones that grant us the unforgettable spectacle of a supernova explosion. Today, I'd like to show you a star that's literally exhaling its dying breath. We're talking about a so-called protoplanetary nebula, nicknamed "Frosty Leo", and this nickname isn't far-fetched at all as I shall explain. 

When a small to medium-sized star reaches the end of its life cycle, it runs out of fuel to sustain nuclear fusion and becomes highly unstable. Its interior collapses and the shock wave that this causes literally blows the star's atmosphere into space, where it will form large gaseous shells or "bubbles" around the remains of the star. The contraction of the dying star's core will in turn generate so much heat that it will reignite fusion of helium into heavier elements, such as carbon, oxygen and even iron. The star's radiation continues to blow up the "bubble", which eventually dissipates into space, and heat it up to a point where the gas ions start to emit light as well. This is what we call a "planetary nebula". 

In the case of Frosty Leo, however, we're not quite there yet. We're actually witnessing the collapse of the star and the initial expulsion of its atmosphere. Its last breath, as a matter of speaking. At this low magnification it's almost impossible to see, but the star's atmosphere is blown away in two opposite lobes which keep expanding at a rate of a whopping 25km/s. Remember that in order to escape from Earth's gravity a rocket needs an initial velocity of 11,2km/s or 33 times the speed of sound, so imagine how fast the nebula around Frosty Leo is forming!

As I said, the nickname wasn't chosen by chance or after a very successful party because its discoverers had to celebrate their findings. No, the nickname derives from the fact that the nebula consists for a large part of... water-ice grains! Plus of course that it resides in Leo. For the time being it's perhaps the only such nebula that we know of, so this makes it doubly interesting. Another weird fact is that it lies 10,000 light-years away from us and an unusual 3,000 light-years above the galactic plane. Therefore it must have been a very lonely star, condemned to die in complete isolation.

In the next millennia Frosty Leo will keep expanding and eventually the nebula, which currently only reflects the light from the star, will light up, adding another Crystal Ball or Eskimo to our skies. But let's not be impatient. This object is already a great spectacle and much more so from a scientific standpoint. 

Monday, 30 April 2018

M94: a galaxy that's difficult to explain

In the area of the M51 group of galaxies, but considerably closer to us, at 16 million light-years, lies this little treasure. M94 is definitely one of the most spectacular galaxies in the Messier catalogue, as we see it face-on and also given it's fairly high surface brightness. In larger telescopes it becomes obvious that this isn't just a normal spiral galaxy but that it consists of a bright inner ring (with complex spiral structure), some 50,000 light-years across, and a faint outer halo that extends at least 30,000 light-years beyond that. 

For the time being, scientists are having difficulties finding a plausible explanation for this odd, double-ring shape because both the accretion of a smaller galaxy or interaction with a neighbour don't seem to add up in this case.  What's more, there appears to be very little dark matter present in it. This is very controversial because current models fail to explain how a galaxy could form without a sufficient amount of dark matter.

There's more. At first it was believed that the bright, swirling inner structure was by far the most active region in this galaxy and we do observe some serious star-forming there indeed. Recent IR and UV studies, however, revealed that the outer halo is not an ordinary ring of stars, but a complex structure of spiral arms which is surprisingly active. In fact, there's twice as much star formation going on in this outlying region and also this raises some eyebrows. A possible explanation could be that star formation in the outer halo is simply more efficient.


Sunday, 22 April 2018

M63: a spring sunflower

Sunflowers are usually a thing of summer, but there's a very peculiar one that blooms in spring already. Point your telescope, or even your binoculars, under the big dipper's handle and you'll easily find this spectacular galaxy. Number 63 on Messier's list looks very much like a sunflower indeed, with it's bright, yellow core and flocculent spiral arms. Unlike "grand design" spiral galaxies, the spiral arms of M63 appear patchy, like a heap of cotton balls. It was also one of the first galaxies in which a spiral structure was recognised, by Lord Rosse, halfway the 19th century. 

The Sunflower Galaxy lies approximately 37 million light-years away from us and is a part of the M51 galaxy cluster, along with a few smaller ones. 

Physically, the Sunflower is a very active galaxy and every knot is an area of intense star formation. More interestingly, photographs revealed a wide halo around it which materialised most likely after an encounter with a dwarf galaxy, somewhere within the last 5 billion years. From the specific properties of the stars in this halo, scientists believe that this dwarf galaxy might have originated in our own local galaxy group.

Now as for the cherry on the cake: look slightly to the left of our Sunflower and you may spot a tiny smudge. No, it's not an extended part of M63, nor is it an accompanying dwarf galaxy. It's proper motion, a breathtaking 23,500km/sec away from us or almost 8% of light speed, is far too great for it to be anywhere near M63, or within the boundaries of our area of the known Universe. It's a giant galaxy, denominated PGC4018103, three times the diameter of our Milky Way, that lies 1.2 BILLION light-years away from us. As such, it's probably the most distant object I've observed so far. Just imagine... The few photons of this galaxy that I managed to capture with my eyes, left their origin when the first multicellular life-forms emerged in the Precambrian seas.