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. 


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.