A user on the forum asked me what I meant by the word ‘random’ in my previous blog post. A statistician could explain this more precisely, but I’ll give my understanding of it in an astronomy context.

A random process is one in which a variety of alternatives could occur, but beforehand we cannot know which alternative actually will occur. The alternatives need not be equally likely, and the probabilities of each alternative happening (the probability density function) may be known very well. If we repeat the process many times, the number of times each alternative occurs will be very close to the probabilities we might already know. But we don’t know which alternative will actually happen each time the process occurs.

A random system is one which arises as a result of random processes. Everything has some element of randomness in it, nothing is perfectly ordered, but some things have a lot more order to them than others. The chair you are probably sitting on while reading this is a highly ordered system. Even though the atoms in it are jiggling around randomly to some extent, their overall motions are generally very ordered. The random motions of the atoms are not very large compared with the order that was instilled in the chair when it’s materials were constructed, whether that was by metal cooling in a mould or wood slowly forming in a tree.

The motions of stars in a spiral galaxy disk have a lot of order to them, as they are mostly formed by relatively gentle physical processes that maintain information about the history of the system. The galaxy started rotating long ago, and the stars which formed in it are still rotating today. In an elliptical galaxy some process has happened, for example a merger of two galaxies, which disturbs that order. The random process at work is the multiple close interactions of pairs of stars. The motion of two stars after they have passed close by one another is very dependent on the exact values of their motion before the interaction. If each of those stars then interacts with other stars we quickly get to a state where we could never know the stars’ initial motions well enough to predict their motions at a later time. This is an example of a chaotic system, and it can even occur for three objects interacting through gravity, never mind the billions of stars in a typical galaxy. There are many alternative paths the stars could travel along, and beforehand we don’t know which paths the individual stars will take. Despite this, we can go part way to determining what the result will be overall, a big fuzzy ball. The stars in elliptical galaxies are not moving totally randomly, there are certain ranges of orbits that are more populated than they should be for a truly random system. This order is a ‘memory’ of the initial motions of the stars in the merging galaxies. However, most of the stars’ movements are dominated by random motions.

Galaxy Zoo features in this week’s Carnival of Space, a collection of all the best space blog writing from the past seven days. This week it’s in a 50s detective story format…and it’s definitely worth a look.

Kevin asked whether I could provide an entry on our efforts to figure out just what Hanny’s Voorwerp might be. This is definitely a guest blog – I am not a ZooKeeper, but they have been gracious enough to let me feed some of the less delicate animals on occasion.

As a reminder, Hanny posted this object on galaxyzooforum.org back on August 13 (I can’t believe it was that long ago now, but apparently the topic scrolled way down in the forum until early December). It showed up on the SDSS color rendition as a deep blue, irregular cloud, just south of the spiral galaxy IC 2497. Pulling out the brightness measurements from the Sloan data in all five filters gave a very unusual result. This thing looked so blue in the color images (made from the gri images) because it puts out almost ten times as much light coming into the g filter as any of the others, and isn’t even detected in the very-far-red z band. That suggests that there is a very strong emission line somewhere in the wavelength range of that filter, about 4200-5500 Angstroms. The SDSS images do show a small object at the north tip of the blob with a more continuous distribution of light; the location is suspicious, but we don’t have direct evidence yet whether it belongs to the Voorwerp. The blob does show structure in the g image, like shells or loops.

Archive searches turned up a radio source in IC 2497, and nothing else helpful (the object just appears on the old Palomar Sky Survey blue-light photographs). A single emission line in that wavelength range could be almost anything, although it was a bit odd that no other emission line was bright enough to produce much light in the other filters. It might be some kind of small nebula in our own galaxy (really small so its dust didn’t block our view of IC 2497 just to the north), some kind of ionized gas cloud associated with IC 2497 itself (redshift z=0.05), or something like the “Lyman α blobs”, gigantic glowing gas clouds seen only in the early Universe (z=3 or so). A spectrum would tell which (if any) of these was correct. So I started emailing friends who use appropriate telescopes pretty regularly, and mostly ended up grumbling about the shortage of spectrographs on 1-3 meter telescopes these days. Meanwhile, I was able to do some measurements with the SARA 0.9-meter telescope, which our university operates remotely as part of a consortium. (In fact, I did these measurements sitting at home, assisted by one of our cats who finds a logbook in front of a monitor the most comfortable place in the house). It takes a pretty long time for a telescope that size to surpass the quick-look Sloan image, but these data were able to narrow down where that strong emission line could be. I used a different set of filters, the classic BVRI set which were designed to be optimized for certain measurements of stars (rather than galaxies), but are helpful here because they’re different. The bright peak made it into the V filter but not the others. The V band runs more or less from 5000-5900 Angstroms, so the wavelength we seek is in the overlap between v and [i]g[/i] between 5000-5500 Angstroms. Alas, that didn’t help us much, since the strong [O III] emission line at 5007 Angstroms would land in that range for something very nearby or at the redshift of IC 2497.

Finally, some of the UK zookeepers were able to find a colleague working at the 4.2-m William Herschel Telescope on the island of La Palma who was able to get a spectrum, while some of us were at the big meeting of the American Astronomical Society in Texas (just last week). The WHT is very well equipped for spectroscopy, and La Palma is a superb site (from which I’ve seen the sharpest images from any telescope I could put my hands on). We’ve got a quick-look screensnap of the spectrum, and it answers a couple of questions right away. The Voorwerp is at almost exactly the same redshift as IC 2497, and almost certainly associated with it. The strong and narrow emission lines are what one would see from a star-forming region. But there are some things about it that are strange, and need more work.

I’ve labelled some of the emission lines in the spectrum here. The spectrograph slit was oriented roughly north-south, running through IC 2497 as well, and is shown left-to-right. Wavelength increases from bottom to top; this is a slice of the violet-to-green region, from about 3400-5100 Angstroms in the reference frame of the object itself. We see the hydrogen series (labelled as H+Greek letters), produced when electrons join with free protons to make hydrogen atoms. There are also lines from heavier elements; the brackets denote so-called forbidden lines, radiation which arises from decay of energy levels excited by collisions between ions and electrons. Looking at what we can tell so far about the relative strengths of these features, there is funny business afoot. First, the gas is hot (even by the standards of ionized nebula). The ratio of [O III] lines between 4363 and 4959+5007 is sensitive to temperature (for those who really want to know why, here is an online lecture including details, with abundant thanks to the late Don Osterbrock for pounding this stuff into my thick head). To have the 4363 line even detectable, the gas has to be unusually hot, more like 15-20,000 K (exact numbers are pending getting the final calibrated spectrum from the observers). Even odder are some of the other lines. He II is produced when an electron joins a bare helium nucleus, and requires high enough temperature or radiation with enough energy to tear both electrons from helium (four times harder than for hydrogen). We don’t see this in star forming regions. The only stars hot enough to produce He II in surrounding nebulae are the central stars of planetary nebulae (which are the hottest stars known, but only for a few thousand years) and a handful of X-ray-bright stars usually associated with accretion onto black holes or neutron stars. On top of that, at the blue end of the spectrum is [Ne V]. If it’s hard to rip two electrons from helium, it’s that much harder to pull four from neon lights. This requires 97 electron volts (eV), compared to 54 to make He II and 13.6 to ionize hydrogen. [Ne V] does sometimes show up in planetary nebulae, but even there calculations suggest that it’s not the UV starlight that’s responsible, but that high-speed shock waves may be the culprit. This line is also common in the spectra of active galaxies – Seyfert nuclei and their kin, where we know that there are abundant X-rays interacting with the gas.

So the spectrum tells us where the Voorwerp is, and leaves us with a fascinating conundrum. (To quote an email from a ZooKeeper, “Hmm..that doesn’t make any sense! Excellent…” Not only do we see these high-ionization lines, but we can already see that they come from the whole cloud, not some small bright region. Are we dealing with shocks, or perhaps with radiation from an active nucleus in IC 2497 which is obscured from our point of view but shining full force toward the blob? Or something we haven’t thought of? All good questions. We’ll know more when we have the calibrated spectrum so we can do detailed numerical comparisons.

There are obviously a lot more observations we’d like to have. The gas is shining so brightly that it’s hard to tell what the stars are doing. We’re putting together a request to have the Swift orbiting observatory take a look with its UV camera and perhaps in X-rays as well. Swift was designed to follow up gamma-ray bursts, but they also take requests for where to point while sitting there waiting for a random burst to go off. And not too long from now, it will be the season to propose for Hubble imaging and spectroscopy with the Gemini telescope’s integral-field unit (which gives the spectrum not just along a line, but at every point within a small area of sky).

Whatever this is, it’s rare. After I mentioned wanting to improve my SQL fu to check for more things in the SDSS with its odd colors, Chris Lintott did just that. There are no more things in the survey database which are not imaging artifacts and have colors within 15% of what we see here. There’s more work ahead to make sure that we include the possibility of, say, having H-alpha not fall between the r and i filters as it did here, but there can’t be many more of these. Rare objects suggest rare events, just the kind of thing that it takes a deep sky survey and careful winnowing to find. Dank U wel, Hanny!

I suspect this is finally the last post relating to the AAS meeting, but I wanted to share the slides from my talk last Friday. Please note that these results are officially provisional! Talks at the AAS are just 5 minutes long (with so many astronomers it’s hard to find space) and I was definitely pushing my luck cramming this much in. As you’ll see, I’m not really one for lots of words on slides so I’ll write a brief commentary between them.

All slides are copyright the Galaxy Zoo team and shouldn’t be used without permission.

While we were at the AAS, Jordan and I were interviewed by Pamela Gay of Astronomy Cast. You can hear the results over at Star Stryder. (The good news is it’s audio, so you don’t have to worry about my shirt…)

I’m back from the AAS meeting in Austin. Last week, Chris and I reported on some of our experiences at the meeting; I know many of you said you wished you could be there, so we wanted to give you a peek at what a scientific meeting was like. There were a lot of posts flying furiously, so this is an index of what we reported on, both here and on Chris’s blog. For more perspectives on the goings-on at the meeting, see the Astronomy Cast LIVE blog. The meeting went from Tuesday to Friday, so this is indexed by day.

Tuesday:

Chris wrote about the search for extrasolar planets, both the progress being made and the postponement of some other missions.

Then, Chris posted some highlights of research presented on Tuesday, including three results that have implications for Galaxy Zoo: a study of the importance of classifying galaxies by eye, the discovery of a spiral galaxy that appears to rotate backwards, and the discovery of a voorwerp-like blue blob.

Wednesday:

Chris posted some beautiful images of the infrared sky from the UKIRT.

Then, Jordan posted about his experiences at the Sloan Digital Sky Survey booth, answering questions about the survey while wearing a chef’s hat. The purpose of the hat was to advertise a session called “Cooking with Sloan,” which served up hot and fresh galaxy images like the ones you see on Galaxy Zoo.

Chris posted again, about how observers and theorists are both making important contributions to the study of extrasolar planets.

At the end of the day, Chris posted about a talk he went to with the intriguing title of How Astronomers Die.

Thursday:

Thursday was the day of the Galaxy Zoo poster presentation – much more about this tomorrow. We were busy in the morning, but several posts appeared in the afternoon.
First, Jordan posted about pub conversations with a researcher at the University of Alaska Anchorage about the role of scientific research in science education.

Next, Kate and Anze posted about the initial results of the Galaxy Zoo bias study, finding that the apparent excess of anticlockwise galaxies has something to do with human perception and not the universe. They also share some ideas about what we’re doing next.

Then, Chris posted twice in a row, about a study of a galaxy supercluster, then about an interview with him posted on Youtube.

Then, Jordan proudly noted that his chef’s hat had been complimented by a Nobel prize recipient, and later added a slightly embarrassing picture.

Friday:

Friday was Chris’s talk about the science results from Galaxy Zoo – more on that tomorrow as well.

Then, Kevin posted about one of the fascinating and unexpected results of Galaxy Zoo – Hanny’s voorwerp.

We hope you enjoyed our coverage of AAS. The next meeting is in St. Louis in early June; whichever of us is going to that will try to provide you with coverage of that meeting too.