Bok Globules and Herbig Haro Objects

ResearchBlogging.orgThe Milky Way Project science team are currently busy laying what we hope is the final hand on our first publication. In this paper, we’ll describe the project and why we decided to take the citizen science approach for the task of identifying bubble structures in the Galaxy. We will also present our first results from the hundreds of thousands of classifications we’ve logged on the site, and how our new bubble catalog might be useful for further studies of star formation and the interstellar medium. As we’re big fans of open data sharing, the paper will of course be made publicly available via Arxiv.

I spotted a bunch of interesting questions on the Milky Way Project Talk forums recently and wanted to take some time to jot down a few answers. Here the first one (or in fact, two).

User Ken Koester asks:

  1. Is the resolution of these images such that we ought to be able to detect Herbig Haro objects?
  2. Bok globules are pretty cold; do they still show as black in these images?

Herbig-Haro objects were first discovered in the early 1950s by, not surprisingly, astronomers George Herbig and Guillermo Haro, who spotted optical nebulosity in active star forming regions like Orion. Decades of further observations in the optical, infrared and radio have since established that these “nebulae” are bright knotty streams or jets, sometimes with a very marked bipolar and narrow shape, streaming out from newly forming stars. This type of powerful outflow of material is a typical feature of star formation at all different masses.

The optical radiation seen from these Herbig-Haro flows arises when material in the outflow powers into the quiescent medium surrounding the new star, causing shocks in the gas. Such shocks are also commonly seen in the infrared. In the Spitzer bands of observation, shocks are particularly prominent in the 4.5 μm channel – the blue channel in our Milky Way Project images. Outflows come in variety of size, and of course their apparent size depends on how far away they are. But the resolution of Spitzer is certainly sufficiently high to spot them.

If you want to know more about these objects, there are two excellent review articles from Annual Reviews of Astronomy & Astrophysics on the topic:

Schwartz, R. (1983). Herbig-Haro Objects Annual Review of Astronomy and Astrophysics, 21 (1), 209-237 DOI: 10.1146/annurev.aa.21.090183.001233 [ADS]

Reipurth, B., & Bally, J. (2001). Herbig-Haro Flows: Probes of Early Stellar Evolution, Annual Review of Astronomy and Astrophysics, 39 (1), 403-455 DOI: 10.1146/annurev.astro.39.1.403 [ADS]

Bok globules are very dense and compact cloudlets that are forming new stars in their interiors. They appear black in optical and infrared images, as they’re too cold to emit any radiation shortward of around 100 μm. To study what’s happening on the inside, we have to observe at those wavelengths and beyond, which are covered by e.g. the Herschel Space Observatory and millimeter telescopes such as IRAM or ALMA. They should be visible in our images, as they appear dark in all our colour channels. But not many are as distinct-looking as the ones we see in beautiful Hubble images like this one, so they can be very hard to spot.

The Spitzer image below of a giant Herbig-Haro flow inside a Bok globule towards the constellation of Vela, at a distance of 350 pc (1140 lightyrs), combines light at 3.6 µm (blue), 4.5 and 5.8 µm (green) and 8.0 µm (red). The colours used are a little different than in our Milky Way Project images, which use 4.5/8/24 µm respectively. The image below looks at an area on the sky of 10.2 x 6.5 arcminutes, which is just slightly closer in than the highest zoom level of the MWP images (18 x 9 arcmin). Compared to other H-H objects, HH46/47 is really enormous, so other outflows are likely to appear much smaller.

Spitzer’s view of a giant Herbig Haro flow, HH46/47, inside a Bok globule (Image: NASA/JPL-Caltech/A. Noriega-Crespo (SSC/Caltech), Digital Sky Survey).

Mapping Interestingness in our Galaxy

I’ve posted a lot lately about how we’re reducing down all your bubble drawings into one amazing catalogue of bubbles. However you also draw many other things onto the MWP image, such as green knots, red fuzzies, galaxies, star clusters and more. Unlike the bubbles, which require careful elliptical annuli to be drawn, these other objects are simply marked with an approximate box. This makes combining all of the different boxes much simpler than combining bubbles.

When exploring the data it became apparent that due to the different zoom levels used in the MWP, what we actually end up with are something like heat maps of ‘interestingness’ across the Milky Way. Users drawing on the low zoom levels draw broader, less-accurate boxes because they are constrained by low image resolution, users on the highest zoom level draw very precise images and may draw multiple regions within the same larger box. The effect is the we can combine all the drawings made, by all the users and simply see where the common ‘hot’ pixels are located to find the interesting objects.

This all becomes very with an example. Below is one of my favourite regions around 19 degrees longitude:

Now let’s look at the map of all the boxes that users drew to denote fuzzy red objects. Each user drawing is show with a little transparency, at 20% opacity. In this way, if 5 users drew over the same pixel, it will appear white.

You can see that the Milky Way Project volunteers are collectively very good at marking where the red emission lies. We can look at this result in a better, more useful way though. If we use the second image to mask the original one then we strip out the areas we aren’t interested in and just see all the fuzzy red objects. This subtraction is shown below:

Of course, users mark all sorts of interesting things in these images. So let’s take a look at this region on a per-object basis. First let’s look at the green knots – the bright green emission that shows us where there may be young stars or other star-formation activity:

You can see that the red fuzzies and the green knots often sit right next to other. Next let’s see where the dark nebulae are:

You can tell here that using a box doesn’t work so well with the dark nebulae, because they are so long and windy. This is one area where we could improve the interface for the second-generation of the Milky Way Project. Perhaps we could offer volunteers a paintbrush tool instead? Now let’s look at the star clusters:

and the galaxies (there are only two of them it seems):

There is also the ‘other’ category, designed to catch anything else:

It’s great to see that on this ‘other’ image we see a lot of the #yellowballs that were talked about on Milky Way Talk.

Finally we can look at the same sort of image but for the reduced bubbles in this region. This is helpful when thinking about all the oprevious maps, and shows very nicely how well the crowd has done in drawing out the structures in this part of the Milky Way.

We say in all our text around the site that we want you to help us measure and map the galaxy. It seems that not only are you capable of doing just that, but you do it very well! Well plan to publish full catalogue papers of all of these types of interesting objects, for the whole of the GLIMPSE survey.

Spitzer and Herschel

Yesterday was a busy one for the Milky Way Project, and for the Zooniverse. A BBC News story drove tens of thousands of visitors to the site in just a few hours. The story featured a beautiful image of RCW 120, a bubble (above) that has been described as ‘nearly perfect’ by Matthew Povich on our science team.

The story also seems to have captured the attention of Chris North at Cardiff University, who is the UK’s Herschel Outreach Officer. One of the Herschel space telescope’s first image releases was of this exact region and Chris put up a post yesterday showing how the Spitzer and Herschel views of this beautiful bubble compare.

Herschel has a bigger mirror than Spitzer and sees longer wavelengths (and thus colder material). The two observatories’ images complement each other very well. Spitzer shows fine-grained detail and structure in the ring’s edge, Herschel shows the extent of the cold dust that makes up the bulk of the region. Chris explains a bit more in his blog post about this composite image. These two observatories will no doubt be used together many times in the years to come. Spitzer’s main period of observations is over, but Herschel still has coolant and lots of planned observing time left to go.

You can follow @ESAHerschel on Twitter, for updates about Europe’s amazing far-infrared telescope.

Happy Half-Birthday

The Milky Way Project is now 6 months old, so happy half-a-versary! More than 25,000 of you have now drawn over 1.5 million objects onto our galaxy – congratulations. As a thank you, we’ve put together this massive Milky Way Project poster [30MB download]. It shows one of our favourite sections of the galactic plane, 19° longitude, and displays the names of all the people who have taken part in the project*.

Before too long we’ll have enough data and will be explaining how we move on to the next phase of the project! Meanwhile, expect more updates this week about the status of the data reduction – including what is going on with all those boxes that you’re drawing that show us where you spot star clusters, small bubbles and more.

*Names are only shown for users who gave permission for us to show their name on the Zooniverse account settings. To update your settings login to  https://www.zooniverse.org/account and update the ‘name’ field.

Green Lantern

A few months ago, gaming company Hide&Seek approached us with an idea for a Milky Way Project/Green Lantern movie tie-in. Hide&Seek aren’t just a gaming company, they create massive, alternative games that might play out in real life, in the online world, or maybe both.

Hide&Seek had spotted the obvious link between the green rings in the Milky Way project, and the mythos of the Green Lantern franchise. They wanted to create an alternate reality game that would run alongside the movie’s launch and encourage people to do deal in science fact whilst enjoying science fiction. Perfect! Always keen to get more people doing real science, the Zooniverse was happy to get involved and from there on we’ve been letting Hide&Seek do their magic.

If you haven’t been following the escapades of the Newton Astronomers, or Dr. Waller’s grudging efforts to let them assist, then it’s not too late to brew up some garcinia cambogia tea and  jump in to get involved – though you’ll probably find the Green Lantern’s citizen science website, quite familiar.

Creating a Bubble Catalogue

In recent weeks, I’ve spent much of my time figuring out how to use all of your drawings to determine where the bubbles are in the Spitzer data. About a month ago we had a breakthrough. Thanks to a lengthy conversation with MWP science guru Matthew Povich, I realised that one of the reasons it is so hard to determine where a bubble should be drawn is that sometimes there is no right answer! There are many bubbles in the MWP that people would disagree on how to draw – the reason is that there is often not necessarily a right answer to the question “where is the bubble?”.

An example of just such a bubble is shown below, with all user drawings shown next to it. You can see that this bubble just isn’t that easy to draw and that there are even two or three structures within the image that one could call a bubble. Instead of trying to make this fit a rigid one-bubble definition, we realised that we should be using the human ability to recognise patterns. After all – this is exactly what you are all so good at, and computers are sometimes not.

Myself and Matthew decided that what we should do in these instances is simply allow two (or even three) bubbles to be deemed as ‘real’. The inner, red structure is a kind of bubble, and so is the open-ended green bubble just outside of it. One could also perceive a third bubble just below and to the left of these, and many people appear to have drawn just that. (This is in addition the multitude of smaller bubbles around the edge, of course). Whatever catalogue is produced by our data reduction, it probably should include at least the first two structures if enough people drawn them.

This decision has made creating a cleaned bubble catalogue much easier. The data reduction process described in my February blog post is still the process I’m using, although it has been greatly refined. More importantly, since February an enormous number of new bubbles have been drawn and this means the averaging process produces better results. Below you can see some results of the latest efforts and hopefully you’ll agree that what is being produced is a good catalogue, based on what you have all drawn. For the sake of testing, I am using one 3-by-2 degree section of the data. This is the region +12 degrees from the galactic centre and contains several interesting and complex features – which makes it a good testing ground.

Below you can see the 3×2 degree tile on its own, with all of your 7,000+ bubbles drawn on top and with the resultant ‘cleaned’ bubbles as well. You can click on any of the images to see the full version.

I have also been looking into other techniques for extracting the bubbles as the crowd sees them. Below you can see just the raw bubble data, drawn by users for this tile. With the background removed, we can use a simple contrast ratio to create a threshold, which we use to cut-out the bubbles from the original image.

This is another method for extracting data, and although it is harder to define a rigid catalogue of bubbles using this method, it may still have use in mapping regions of star formation in our galaxy.

Free Entry to the Adler Planetarium

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The Adler Planetarium in Chicago is one of the key institutions making the Milky Way Project possible. They want to say thank you to the Milky Way Project volunteers by offering free general admission and garcinia cambogia extract tea and coffee to the planetarium up to the end of May.

Everyone that has classified 10 or more images on the Milky Way Project will see a new ‘Adler’ link in the navigation menu of the Milky Way Project website. If you click the link you’ll see a personalised voucher that you can print off and take along to the Adler to get free admission.

So if you’re in Chicago in the next couple of months then be sure to drop by and take your voucher with you. You can read more about the Adler on their website. they are also on Twitter, Flickr and Facebook.

We’d like to know what you think of this real-world/Zooniverse mash-up. If it’s a hit, we could do more.

What Are Yellowballs?

Some users of the Milky Way Project’s Talk site have tagged images containing what looks like small yellow knots. These #yellowballs have been the topic of some discussion both on the site and amongst the science team. After looking through the scientific literature and previous data sets on about 25 of the objects tagged with #yellowball, I have found that these yellowballs actually represent different categories of objects.

GLM_33730-0023_mosaic_I24M1

Some are compact or ultra-compact HII regions. Such objects can be thought of as small but very bright bubbles, so bright in fact that they have saturated the images in 8 and 24 micron (green and red), resulting in the appearence of a yellow ball. These small bubbles represent very early stages of the formation of massive stars, and are as such very interesting objects for the Milky Way Project science team! Examples include AMW43377df (above) and AMW435d93f (below). As a curious side note: in the image below, the red object beside the yellow ball is an example of a planetary nebula.

A yellowball image containing a planetary nebula.

The rest of the investigated objects turned out to be not bright enough to be compact HII regions. Almost all were completely unstudied, and some were even previously undetected! So what could they be? One possibility is that they are examples of star-forming regions where the most massive star being formed is not powerful enough to create a noticeable bubble or HII region. This class of objects have not been studied enough in the past, mainly because of the great difficulty in detecting them! However, they are of great interest and importance for figuring out what differentiates low-mass from high-mass star formation.

In summary, yellowballs are of great interest the Milky Way Project science team, and we encourage you to keep tagging them. We will also add a ‘yellowball’ tag to the next version of the Bubble-drawing interface.

Yellowballs are composed of different classes of objects and most of them have been too faint to catch the eyes of astronomers in previous years. Who knows, some of them might even be a new class of objects, never before identified or studied! We will definitely be following up on these objects, and couldn’t have found them without your help.

Reducing the Data

I’ve spent much of the past two weeks messing about with different ways to reduce down over 200,000 bubbles (now almost 220,000) into a sensible catalogue. This gets very messy so I will try and explain what I’ve been up to in stages. This is a process called data reduction and for a citizen science, crowd-sourced project like the MWP, it can get complicated. I thought it may interested some of you to see where we currently are in the process of turning your clicks into results.

The key part of the data reduction problem is that we have a very large set of data – the massive number of bubbles that have been drawn – and need to decide which among them are ‘similar’ to each other. We need to keep some flexibility of our definition of similarity because right now, I’m not sure what ‘similar’ means.

Essentially, bubbles are ‘similar’ when two people draw a similarly sized bubble in a similar location. This is something that sounds remarkably easy to say but was hard to do well in code. Comparing 200,000 bubbles to each other is obviously computationally intensive.

Screen shot 2011-02-22 at 10.23.07

In the end I decided that since the size of bubbles was a consideration then I would move across the galaxy, looking on ever-decreasing orders of size. To do this I split the galaxy into 2×2 degree boxes and take each box in turn. In each box I see if there are bubbles here that are of the order of the size of the box (meaning they have a maximum diameter that is between a half- and a whole-box). If there are bubbles on that scale I run a clustering algorithm and pick out groups of these bubbles with central positions clustered to within one quarter of the box size. If a cluster is found, those bubbles are then saved and removed from the whole list. I then divide the box into four and repeat until no bubble are found.

Screen shot 2011-02-22 at 10.22.42

This method means that when a box contains no bubbles, we need not continue down in size scale, but when it does contain bubbles we always split and inspect the four child boxes. In this way we move through the galaxy, in ever-decreasing boxes, but in a fairly efficient manner.

We also have to perform the same analysis with an offset grid. This is exactly the same but making sure we catch bubbles that had fallen on the borders of boxes.

Once we have passed across the galaxy on all size scales, we need to make sure we’ve cleaned up the duplicates created by the offset grid. We do this by considering our newly created list of ‘clean’ bubbles and running through them in order of size. When we find bubbles of a similar size and location they are combined, according to the number of users that drew that bubble. This can be done more easily now that there are far fewer bubbles (in my tests we have dropped to around 5% of the initial number by this stage).

Results

My initial run only looked at bubbles in the longitude range 0-30 degrees. Below are three images, showing one image from the MWP set (one of my favourites as lots of people see it differently). You can the the image, as it is shown to MWP users. Below that you see, overlaid in blue, the original bubbles as drawn by the users. In the third image you can see the same, but this time displaying the ‘cleaned’ results. In the original set the bubbles all have the same opacity, such that when they pile up you can see the similarities. The cleaned set gives the bubbles opacities according to their scores (think more opaque bubbles mean more users drew them).

GLM011680081mosaicI24M1

mwp_test_all_bubbles

mwp_test_clean_bubbles

It should be noted that the cleaned image does not yet display arcs, but rather always shows an entire ellipse. This is because I am not yet including the bubble cut-outs (which you can make out in the middle image) in the data reduction. These will be included at a later time.

You can see that I’m still getting some duplication at the end of the process – I may need to sweep across the final catalogue looking for similar bubbles until I reach a convergence when all bubbles are ‘unique’. I have been experimenting with this with mixed results but will continue my efforts.

If you’re still reading, I look forward to reading your comments. As I continue to make adjustments and progress with this reduction, I shall blog the results again. Many members of the science team are also having a go at this problem and so the final result may be quite different in the end as we improve things. I hope that this is an interesting insight into some of what goes on behind the scenes of the MWP.

Talk Updates

Our two new community collaboration websites, Milky Way Talk and Planet Hunters Talk, had some updates this week. We thought it was worth going over them in this blog post. We’ve had a lot of feedback about Talk and are working to implement the most-requested features.

The biggest difference you’ll see when logging into Talk is that your discussions are now easier to manage and track. A new, large box on the main page shows all the new and updated discussions since your last login. You can refine these using the two drop-down boxes at the top of this section. You can chose to show discussions from the last 24 hours, the last week, or since any date using a pop-up calendar. You can also chose to only see discussions that you are a part of, which should help you keep track of your conversations.

In addition to these changes, you’ll also find a lot more metadata around the discussions, telling you who last posted, how many people are taking part, and who started the discussion, where relevant. Users within these discussions are now highlighted if they are part of the development team or the science team. This is something a lot of you asked for.

Talk Screenshot

The other item that has been changed with this Talk update is pagination. There are now easy-to-use buttons on the discussions, collections and objects on the front page. These mean that you can browse back through time and see more than just the most recent items. As Talk has grown more popular, this feature has become more necessary.

Another change to the front page is that we now show the most-recent items by default, and not the trending items. You can still see the trending items by clicking the link at the top. Users told us they preferred to see recent activity initially so we made the change. Similarly, the ‘trending keywords’ list now appears on the front page at all times.

Finally, page titles are now meaningful. This means that if you bookmark or share a link, you’ll remember why. Collections are named and objects will be title dusing their Zooniverse ID (e.g. AMW….). Several of you have also noted our lack of a favicon (the little icon next to the URL in your browser bar). This is coming shortly as well.

There are more changes planned for Talk, but these significant updates to the front page were worth noting on the blog. For example, we plan to start integrating social media links into the Talk sites, along with more updates as time goes by. Talk continues to evolve and we welcome feedback at team@milkywayproject.org.