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.


Tuesday, 17 April 2018

EGB6: Interesting faintness

Yes, I simply love the challenge of spotting extremely faint objects and especially large, frail planetary nebula in the last stage of their existence. As you know, when a star dies, it suddenly expels its outer layers which are subsequently blown away by the violent radiation of the remaining stellar core, the so-called "white dwarf". After many millennia, however, these shells of hot gas grow so large and thin that they start to dissolve in the void of space. This is exactly what we witness here, in this extremely large planetary that was discovered in 1984 by Ellis, Grayson and Bond. Visually this is one of the toughest objects to see and it was not without difficulty that I managed to discern its broken annular shape, with its western rim slightly brighter. Nevertheless it was just a tad easier than PuWe1, which was really on the limit of visibility.

How difficult they may be for us, humble visual amateurs, these extremely old and diffuse planetaries offer a great opportunity for scientific study, more specifically in the way they dissolve into space and how their central star extinguishes. In the case of EGB6, another very interesting discovery was made. Strange infrared emission knots in the spectrum of its central star, pointed to the existence of an obscure companion star, probably a faint red dwarf. Recent observations with the Hubble space telescope, revealed that some of the expelled matter of the central star was captured into an accretion disk around this companion!


Sunday, 8 April 2018

M3: autism power!

I hate sketching globulars. Really, I hate it. The reason for that is obvious... there are simply too many stars to sketch and after hours staring at them through the eyepieces you're overwhelmed with dizziness and a hammering fatigue. You're craving to go to bed and cursing yourself because you stubbornly set out on a job that you knew was going to be impossible from the start. But there you are... half a page filled with stars and still another half to go. Should you give up and let all of those hours of work be in vain? Or should you continue unabatedly, even though you can't think straight anymore and every muscle in your body's throbbing and aching?

In the end it took me almost two nights to sketch all of this, and then almost an entire month behind the pc in order to turn it into a somewhat realistic digital image. So please, don't expect me to do this kind of insane sketch often. 

But perhaps this sketch was appropriate in this time of the year, when we're celebrating autism week, because in a sense this sketch shows what an autistic person is capable of... which extraordinary talents and rock-hard determination may lay hidden under that often absent gaze. 

AUTISM POWER! :-)

About M3, it's one of the brightest globular clusters in the sky, just under the limit of naked-eye visibility. At a distance of 33,900 light-years, it lies beyond the centre of our Milky Way. Only 180 light-years across, it contains some 500,000 stars! Globular clusters are among the oldest entities in our universe, often being older than the galaxy they accompany. Therefore the stars in those clusters are also among the oldest and reddest (coolest). Strangely enough, these globulars appear mostly bright and blue through a telescope. The reason for that is that these stars are packed together so much in such a small volume that their outer layers are often stripped away through tidal interactions, exposing their hot (blue-white) interior. The blue colour I added to many of the stars in my sketch was not observed as such but was added as a random effect to create more depth (a globular truly looks three-dimensional through a binoscope) and to reflect the cluster's brilliance and overall bluish appearance.


Thursday, 15 March 2018

NGC4244: A silver needle

Galaxy season's upon us again... that time of the year where the Earth turns away from the galactic plane in the northern hemisphere and more easily shows us the marvels that lay way beyond our Milky Way. Not that far away from us, at merely 14 million light-years' distance, lies a group of galaxies in the small but wonderful constellation of Canes Venatici, the dogs that hunt the great bear. Last year I already talked about the highly irregular "Train Wreck Galaxy", this year I'm taking you to its spectacular neighbour, NGC4244 or better known as the "Silver Needle Galaxy". 

There's no need to explain this nickname because the minute you point your telescope to it, you'll understand where it came from. It's one of those galaxies we see edge-on and for this reason we see it as a long streak with a brighter and wider area at its core. Yet, from the peculiar clumping of stars along its disk scientists conclude that it must have very loose spiral arms.