Saturday 23 December 2017

IC2087: When dust lights up

This may sound a bit odd, but most of our Universe is actually invisible to our eyes. When we look up at the night's sky and admire that mesmerising blanket of millions of stars, we only see things that emit light, i.e. stars and gas clouds that are heated up so much that they start glowing. But this is only a small percentage of all matter that surrounds us. The so-called dark matter is, indeed, invisible because usually we can't see it in a Universe that is essentially dark. 

And yet, every now and then we can catch a glimpse of all the dark dust and gas that's floating through space. When a cloud of this dark matter drifts in front of a bright stellar background, for instance, or when it reflects the light of nearby stars. In the case of IC2087, we observe both.

On the border between Taurus and Auriga there's a gigantic dust cloud, merely 700 light-years distant and denominated as Barnard 22, which blocks the light of all the stars that lie behind it. Just point your telescope in that direction and you'll agree that there are only very few stars to be seen. Even with my binoscope the field of view looked strangely empty. In the middle of all that darkness, however, you may find the bright patch which is the protagonist of this blog post. IC2087 is a reflection nebula, i.e. that this cloud merely reflects the light of stars that are embedded in it. Careful study of this cloud with infrared telescopes has not only revealed its main light source, but also that this nebula contains a lot of embryonic stars. These baby stars haven't really lit up yet and therefore the nebula remains difficult to see, for the moment. But soon fusion will kick in in the star's cores and the gas and dust will be heated up. Probably, within a couple of hundreds of thousands of years, this nebula will become a spectacular stellar nursery, brighter than the Orion Nebula. 

Tuesday 19 December 2017

PuWe1: Mission Impossible?

There are certain objects which tickle the imagination. You know that they're supposed to be virtually impossible to see with any amateur telescope, and yet the temptation's too strong. No matter how cold it is; no matter having to look for it for over an hour, you simply give in to this nagging crave in your chest and you point your telescope towards a remote corner of the obscure constellation of Lynx. There, in 1980, two Austrian astronomers called Purgathofer and Weinberger, discovered an extremely large, ethereal planetary nebula. It appeared so faint on their original photographic plates that they were unable to present it for printing along with the report of their discovery. Nowadays it has become a challenging object for skilled photographers who manage to capture its delicate structures after many hours of exposure time.

With its extremely low surface brightness of 23.7 mag/arcsec², it has always been deemed impossible for visual observations. But, as loyal readers of my blog will know, impossible is my middle name. What's more, I've got just the perfect instrument for large and extremely faint objects at my disposal. A binoscope effectively collects the same amount of light as a telescope 1,42 times its diameter, but... it offers that amount of light at a much lower magnification. I won't bother you with the technical explanation of all this, but suffice to say that the lower magnification allows to concentrate the frail light of the object on a smaller surface. In other words, you see it more clearly. How clearly? Well, don't get overexcited. After having stared at the right spot for at least fifteen minutes, I daresay that I did see "something". Yes, there was a broken circle of extremely faint nebulosity. It must be the faintest and most difficult object I've ever observed, even more so than oddities like ARO215. Yet, that's exactly the thrill that we faint-fuzzies lovers get from it. You know that it's on the edge of impossible. You're freezing, your limbs are giving in, your eyes are having difficulties to focus. But then... suddenly... that extremely faint arc reveals itself. And it was all worth it.

PuWe1 is one of the nearest planetary nebulae, its distance estimated at under 1,200 light-years. As you might have guessed, it's also very old and has extended over 6 light-years across in the last 20,000 years. Let's enjoy the show while we still can, because it won't be long before this nebula will be gone forever.

Friday 15 December 2017

IC417: the yellow spider

Rounding off my series about vast and faint nebulae in Auriga, I present you with IC417, otherwise known as the Spider Nebula. Again, it's not an easy object for visual astronomers but with a sufficiently dark sky and generous aperture you should be able to spot it. Although the nebula is a hot star forming region and would therefore benefit from the use of filters, I decided to make my observation without as I shall explain. 

The nebula complex lies somewhere around 7,500 light-years away, in the outlying Perseus arm of our galaxy. As I said, it is another giant stellar nursery in the heart of which we find a lovely, somewhat elongated cluster of young stars, denominated Stock 8. Interesting to note is that these young stars seem to have different ages, ranging from 1 to 5 million years, which indicates that stellar formation has continued over a long period of time here. 

Now let's turn our attention to the bright, yellow star which appear to be the protagonist of this sketch. As you might have guessed, this star (Phi Aurigae) is much closer to us, at a distance of 450 light-years, and is already visible to the naked eye under suburban skies (mag. 5.05). It is an orange giant (although I saw it rather as bright yellow), meaning that it has evolved off the main sequence and is now fusing helium into carbon and oxygen. Although nearly 300 times as bright as our Sun and 31 times its diameter, it does bear a lot of similarities to our star. For starters, it weighs in at 1.2 solar masses and it has a very similar chemical composition. In fact, it's a perfect example of how our Sun will look like in about 5 billion years, after it'll have consumed all of its core hydrogen.

I guess this is just an optical illusion, caused by the brightness and deep colour of Phi Aurigae, but I had the impression that the nebulosity in its immediate vicinity also had a slight yellowish hue. The sight was so lovely that I wanted to capture it this way, rather than to use nebula filters which make all stars appear blue.

Friday 1 December 2017

NGC1893 and IC410: surrounded by tadpoles

Just one and a half degrees south-west of IC405, we find NGC1893, a young star cluster that lies embedded in the nebula from whence it originated some four million years ago. Even from its respectable distance of 12,000 light-years it shines with a magnitude of 7.5 and is therefore an easy target for binoculars. 

The nebula itself is quite a different matter. With its petals whirling around a dark centre, it closely resembles the Rosette Nebula, even though it appears much fainter and smaller due to its distance. In reality, this nebula spans over a hundred light-years across, four times the size of the Orion Nebula! From Earth, you need a medium to large telescope in order to see it and special nebula filters help as well. These filters block all light, apart from the very specific frequencies which these kinds of nebulae emit. The result is that the background and the stars significantly darken but the nebula doesn't. Therefore it becomes more visible because you get a lot more contrast. 

With my binoscope I was able to see some very interesting structures around the central void. The reason why the nebulosity disappears at the centre is because it's being blown away by the radiation of the hot, young stars that have just emerged from it. So here you're looking at a star-forming nebula in a somewhat advanced state of its evolution. As more stars are born, radiation and stellar winds increase, expediting the nebula's evaporation into space. 

Another interesting feature about this nebula is that it contains "tadpoles". They're extremely difficult to see with amateur telescopes and also I was only able to see two of the "heads" (scientifically referred to as "Simeis 129" (top) and "Simeis 130" (bottom)). Just left of the cluster's central stars you'll see two little knots in the nebulosity. The "tails", gas plumes that are blown away from these "heads" and eroded by a powerful stellar wind, were unfortunately invisible to me.