The Most Distant Bubble?

A little while ago Sarah Fitzmaurice, a work experience student at Zooniverse Oxford, spent a week working with the Milky Way Project database. She did some fun things with the data, including plotting the locations of many of the bubbles according to their distance from us. For many, the current canonical view of our own Galaxy comes from a combination of data sources, compiled by Robert Hurt, working at NASA JPL. The image is shown below, and you may recognise it: we use it as our Twitter/Facebook avatar. It is an artist’s impression based on several data sources and guided by astronomers.

The Milky Way may be our home in the Universe but we know startlingly little about it. On key missing piece of information for many objects in our Galaxy is their distance from us. From the Spitzer data alone, we do not know the distance to the bubbles in the MWP. For our first Data Release paper, we compared the MWP Bubble catalogue to known objects, some with distances, and this allowed us to find  out how far way some of the bubbles are. This enables us to investigate how large and sometimes how massive they may be.

During her work experience week, Sarah plotted the bubbles with known distances onto Robert Hurt’s map of the Milky Way. The result is shown below. The bubbles are marked with crosses, and the size of the cross shows the relative size of the bubble. The distances to these bubbles were derived by comparing them to a known set of radio sources that are expected to look like bubbles in Spitzer data.

You can see that the bubbles generally follow the distribution of spiral arms and that it is easier to see the bubbles nearby than those farther away. This is good because it is roughly what we expect. This map also allows us to easily spot the isolated, nearby or most-distant bubbles in the project. Much of Sarah’s week was spent looking at each of the interesting bubbles and finding out some more about them.

Although there may well be more distant bubbles in the catalogue, Sarah’s map provides a candidate for ‘most distant bubble’ in the MWP. It is one of a pair of bubbles located on the far side of the Perseus arm, almost 45,000 light years away from the Sun – in the top part of the above image.

Using the new MWP coordinates tool we can take a look at this distant object, and two nice images of it are shown below. Our ‘most distant bubble’ is actually located within another larger, clearer bubble, the image of this is also given. This is a line-of-sight effect and they are not necessarily near each other.

This bubble is located literally on the other side of our Galaxy and is roughly 15 light years across. The fact that the two bubbles are positioned on top of each other makes it hard to decide which one is farther away. There are many more instances where bubbles lie on top of each other where it would be impossible to decide which is actually on top of which. The nebulous material of which these objects are made makes them hard to disentangle. In this case there are stars and IR objects on top of the smaller bubble that make it easier to pick out the nearer and farther bubble.

In this case, the distance value is derived from a radio source that we expect to be associated with a bubble. Both of these bubbles lie at roughly the correct position to be associated with the radio source. Since we know the radio source is very far away, we can say that the smaller bubble is most likely the object associated with the radio source.

These kinds of confusing caveats are one of the things that make Galactic astronomy difficult and challenging. For these reasons, this might be the most distant bubble we know of in the MWP – or it might not. Either way, this awesome little bubble has provided the opportunity to discuss the ways that we determine the distances to objects in the MWP catalogue, and how doing astronomy in our cosmic backyard is tricky territory indeed.

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A bright bubble around a dying star

The bright bubble around Luminous Blue Variable star G24.73+0.69

A few days ago Milky Way Project user suelaine posted an image of this pretty bubble on the Talk forum, asking whether it was a supernova. As supernovae – or rather, the debris that’s left behind after they explode – often have this kind of shape, I initially thought she was right. But when I looked up the coordinates on SIMBAD – the astronomer’s guide to the Galactic sky – I discovered it was a beautiful example of a more peculiar type of object: a Luminous Blue Variable star (LBV).

[As an aside, the SIMBAD page for the object is a little confusing, as it’s identified on there as a Be star – a rapidly rotating B star. But when you look down the page at the references, it’s clear that the star has since been identified as an LBV star, probably even more massive than originally thought.]

LBV stars are massive stars, often with a few tens of times the mass of the Sun, that are approaching the end of their lifetimes. The fuel in their cores, needed to maintain nuclear fusion, is running out. This makes them unstable, causing them to flare up at intervals. As they’re not able to hold on to their outer layers, powerful winds eject matter into the surrounding interstellar medium during these eruptions, and the star can be sen to brighten significantly over several months. LBVs are on their way to exploding as supernovae.

The evolution of such massive stars once they run out of fuel proceeds very quickly, so these objects are extremely rare: only around a dozen are firmly known in the Milky Way Galaxy. The best-known examples are Eta Carinae and the Pistol Star,  perhaps the most luminous star in the entire Galaxy. Because there are so few LBVs to study, there’s a lot about them we don’t know.

This particular LBV, prosaically known as G24.73+0.69 (its galactic coordinates), was discovered in 2003, and lies at a distance of around 5 kpc, or 16000 lightyears. As well as the compact orange bubble this larger view of its surroundings shows that there is a second, larger shell, more bipolar in shape than a true ellipse. The star and its environment were studied in detail in a very recent paper by Argentinian astronomers Petriella, Paron and Giacani. They discovered a dense molecular shell tracing the outer bipolar nebula. They suggest that the inner compact bubble is the result of an LBV eruption, and the outer bipolar shell perhaps caused by more gradual mass loss during the star’s “regular” lifetime.

Interestingly, they also find evidence that perhaps new stars are forming near the lobes of the larger shell. They suggest this may be triggered star formation in the swept-up gas, but their observations can’t confirm that.

I didn’t know much about LBVs myself, so I was pretty excited with this find. Keep posting your interesting objects to the forum – perhaps we can find more LBVs or other cool types of objects.

If you’re interested in learning more about this interesting star, here’s the full paper reference:

Petriella, Paron & Giacani. The molecular gas around the Luminous Blue Variable Star G24.73+0.69. Astronomy & Astrophysics vol. 538, A14 (2012) [pdf available from Arxiv]

Triggered Star Formation

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There’s a new Milky Way Project paper out on the arXiv. It was submitted to the Astrophysical Journal last week and concerns the topic of the triggered formation of massive stars. This study was lead by Sarah Kendrew and utilises the results of the first MWP paper (our catalogue of bubbles).

One of the main reasons for undertaking the MWP was to produce a large bubble catalogue that would allow statistical studies of star formation sites in our Galaxy. In the end we produced a list of bubbles ten times larger than the previous best catalogue in our first data release (DR1).

In this new study, we’ve used statistical techniques to see what correlations exist between the MWP bubbles and the RMS Catalogue: a well-used catalogue of infrared sources along the Galactic plane (a similar region to that covered by the Spitzer data used in the MWP).

The paper looks for any signs that there is a correlation between the positions of RMS sources and the positions of the MWP bubbles. Specifically we’re trying to see if such massive young stellar objects (MYSOs, stars being formed) are most commonly found on the rims of bubbles. If this is true, then it adds to evidence for a mode of star formation where the formation of some stars triggers the formation of others. In this case, young, hots stars blow out a bubble in the interstellar medium. During this process, clumps of material occur in which new stars condense and form.

This new study finds a strong correlation between MYSOs and the MWP bubbles. We find that Atwood thirds of the MYSOs surveyed are associated with bubbles and 22% are associated with bubble rims. We also see that larger bubbles are more likely to have MYSOs on their rims – though one of the main issues we encountered is that the effect of line-of-sight confusion makes the situation complicated.

This second paper is the first to follow on from the MWP DR1 paper, and there are more planned. You can read the paper on arXiv. The Milky Way Project itself, and this study, we’re presented at the UK/Germany National Astronomy Meeting this week in Manchester.

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Milky Way Project Refresh

We’re excited to announce that we have updated the Milky Way Project to show you more bubbles and to produce even more science! After creating our catalogue of 5,106 bubbles earlier this year, we’re aiming to try and refine and improve our measurements of the MWP Bubble catalogue by asking you to measure each and every bubble in greater detail. This means that for a while we’ll no longer be displaying images from across the plane of our Galaxy, but instead we’ll just be showing you images of regions where you told us that bubbles are located.

Our recently accepted Data Release 1 (DR1) paper, ‘A Bubblier Galactic Disk‘ is already online and being used by astrophysicists to help better understand star formation in our Galaxy. Later this month we’ll be presenting the MWP at the UK/Germany National Astronomy and SEO Consultant Meeting in Manchester. We will hopefully be able to bring you some updates at that time so you can follow along. In that paper we estimated that our rate of discovery of new bubbles had declined over time to the level where only a few new bubbles were being discovered each month. This make sense of course. The more people that inspect all the images on the site, the less likely it is for a bubble to remain undiscovered. What becomes important are the multiple, independent drawings of each bubble. To reflect this, we have updated the MWP site to shift from showing random portions of the Galaxy, to showing the places we believe there are bubbles – based on your classifications. Each image you are now shown on the site contains one of the 5,106 bubbles contained in the DR1 catalogue. It’s seems really fitting that the MWP community is now inspecting the very catalogue it created.

This update to the site has two effects. First of all it means that you are able to see each bubble more clearly and thus make more precise measurements of their shape, size and thickness. It also means that you see a lot more bubbles! There now ought to be at least one bubble in every image, which is a lot of fun. It also means that Talk has been updated with a host of new bubble-centrd images, showing off all 5,106 of the DR1 catalogue’s bubbles.

We have made some other updates to the site as well. We have put up our contributors page, which lists the names of everyone that made the DR1 paper possible. We have also finally added the term ‘Yellow Ball’ to our list of objects you can mark in images. The #yellowballs are a term coined on Talk by the MWP community and turn out to be interesting to researchers at they appear to represent ultra-compact star forming regions.

Don’t forget to follow us on Twitter @milkywayproj for the latest updates, and our Facebook page too.

Data Release 1

We submitted the first Milky Way Project paper to the Monthly Notices of the Royal Astronomical Society (MNRAS) in December and the referee has been very kind to us so far. We have our fingers crossed for acceptance soon. Thanks to recent media coverage and some awesome buzz at the recent AAS meeting we decided to go ahead and post our paper to the arXiv yesterday. In addition to the paper, which explains how the catalogue was created from all your bubble drawings, we have also made the data available on the MWP site. You can explore the data graphically or download various files on our data page.

DR1

Data release 1 (DR1) currently consists of a catalogue of large bubbles, a catalogue of small bubbles and a set of ‘heat maps’ (more on that in a moment). We are aiming to add green knots, red fuzzes, star clusters and galaxies to this list later in the year. We’ve called it DR1 because we also hope to refine and improve our catalogue – partly based on feedback from the community – and release a second set of data (DR2) later in 2012. Hopefully 2012 will be a big year for the project!

We have also nearly finished the process of cresting our ‘heat maps’. These are the maps of raw clicks that show the true crowd-sourced view of where bubbles are locate din our galaxy. they look amazing and are incredibly detailed and rich. They represent something new for the Zooniverse, and for the scientific community, and it will be interesting to see if they can be useful when released into the wild. If you’d like a sneak peak you can download one of the 3°x2° regions of the galaxy here and try it out – this is the region seen in the image above. It is a 5.4 MB FITS file, centred around 18° Galactic longitude and shows the raw bubble drawings that were used in the DR1 release. Every bubbles is given the same, tiny opacity and so as the bubbles coincide we start to see the regions of the sky where every agrees that bubbles are present. (A 220 MB file of public Spitzer data for this region can also be download as FITS here, for comparison.)

The other big change that we need to make to the site in the next few days is the release of an official ‘authors’ page, crediting all our citizen scientist volunteers. 40,000+ individuals have taken part in the MWP and those who contributed to DR1 will be credited on the site soon. I’ll blog when that happens to let you know.

Keep Clicking!

All of this doesn’t mean the MWP is over though: far from it. In fact, the classifications you make now will be collectively refining and improving the data we have produced so far. We  have plans, which i’ll explain at a later time, to modify the MWP interface so that each classifications contributed more efficiently to the final result. We also have new data to come in 2012 that will mean we can search for bubbles in whole new regions of the sky. Very exciting and there is much to look forward to in 2012!

Exploring the MWP: Coordinates and SIMBAD

One of the most common questions posted on Milky Way Talk is “What is [that thing] in this image?”, and science team members try to respond to some of those where we can. The galactic plane is so incredibly rich at these infrared wavelengths and the Galaxy is so vast that even with the combined experience of the whole science team we usually don’t know the answer.

To help everyone out, we’ve created a new tool that lets you search one of the world’s best astronomical databases from within the Milky Way Project. SIMBAD is a huge astronomical database, maintained by the Centre de Données astronomiques de Strasbourg (CDS) and contains 7 million astronomical objects documented in the literature. When astronomers want to see what is known about any part of the sky, many of them start with a SIMBAD search. Our new Coordinates Tool lets you search the images from the MWP for SIMBAD data, to help show you what different objects are.

The Coordinates Tool

You access the new Coordinates Tool directly at http://www.milkywayproject.org/tools/coordinates/

This will take you to a default page, exploring the area around the coordinates 0, 0. The MWP images use the galactic coordinate system, which expresses positions in galactic latitude and longitude – concepts that should be familiar if you know about geo-coordinates here on Earth. The “equator” of the galactic coordinate system (the latitude = 0 position) is roughly coincident with the disk of the galactic plane.

Looking down on the galactic plane (Image: NASA/JPL-Caltech/R. Hurt)

In this picture, the galactic latitude tells you how much an object lies above or below the plane of the Galaxy, and the longitude specifies the angle away from the Galactic Centre. The above image shows a schematic diagram of what we think the Milky Way Galaxy looks like, with an indication of our own location and a galactic longitude grid. Galactic latitude runs from -90 to 90 degrees, and longitude from 0 to 360 degrees, although sometimes you may also see it noted as -180 to 180 degrees.

To search the area around any set of coordinates, you simply include them in the URL for example, to search one of my favourite regions, at longitude 18.4 degrees and latitude 0.2 degrees, you would visit

http://www.milkywayproject.org/tools/coordinates/19.0/0.0/

This will display one of the MWP images that containing those coordinates (see below). It will also list the other MWP images containing these coordinates. This lets you explore the region at different scales and in different contexts. The specified coordinates are shown on the image with a box. A link to the image’s Talk page is also included.

You’ll see that as you move the cursor around the image, coordinates are displayed to help you navigate. You can double click on any point to jump to that centre and see the images available. By default a small, square box is drawn onto the target area. If you want to draw a specific box you can give the width and height (in arc minutes) as URL parameters:

http://www.milkywayproject.org/tools/coordinates/19.0/0.0/?h=15&w=30&zoo_id=AMW102de6d

You can also reach the Coordinate Tool from the main Explore page. just double click on the map to just to more detail on that region. A link has also been placed on the images in the My Galaxy section of the site, for logged in users.

SIMBAD

Also present on the Coordinate Tool is a button with the words ‘SIMBAD Search’. Clicking this performs a SIMBAD search on the current viewing area and displays the results directly on the image. Here’s an example from the URL I gave above:

Any objects SIMBAD finds in the astronomical literature are displayed as circles. If,you hover your mouse over them you will see their object name and type. Clicking on these objects takes you to the objects page on the SIMBAD site, where you can find out more.

Many of the objects found in the MWP will be stars – the galaxy is full of them! – and many will be IRAS and 2MASS objects – these names derive from previous infrared surveys that mapped the regions covered by the MWP data. In the above image you can see one 2MASS object near the centre of the bubble on the right:

The SIMBAD page for 2MASS J18252813-1224187 explains that may be an Asymptotic Giant Branch (AGB) star. These objects are interesting, and there are plant of them to be found in the MWP images.

Some interesting regions that are worth a SIMBAD lookup with the tool include the rim of a broken bubble, a dying star and the pulsating heart of a gorgeous bubble.

This tool is still a bit rough around the edges, but we are keen to invite comments and ideas from anyone that would like to try it out. You can either leave comments on this blog post, or email us on team@milkywayproject.org. We have more updates on the way!

First Paper: A Galaxy of Words

The first Milky Way Project science paper has been submitted! We sent off our manuscript to the Monthly Notices of the Royal Astronomical Society just yesterday – exactly one year since the launch if the project. Now we wait for the process of peer-review to get kick-started. Our paper will be sent to an independent referee – another researcher in astronomy – and usually we would then get some corrections along with a thumbs-up or -down for publication in the journal.

In the field of star formation it is customary to wait until the referee has given us the OK before we publish a pre-print of the paper online. So we will keep you posted on progress – including posting a PDF of the paper when its time – as we move toward publication.

In the meantime, as part of the Zooniverse advent calendar we’ve produced a slightly different version of the paper for publication right now! This ‘word galaxy’ is a representation of the content of the paper – but in beautiful spiral form. The most common words in the paper were MWP (214 times) and bubbles (283) so they are largest. The words scale all the way down to disk (3 times) and ‘tend’ (2 times).

Have fun exploring the paper in this form until we can get the real one to you in the next few weeks.

[Download large version 2.6 MB]

Bubbles on the Tree

We’re often told how festive the images in the Milky Way Project look – so for the Zooniverse Advent Calendar we’ve made some festive MWP tree decorations. You can download these template PDF files (first, second, third), follow the simple instructions, and you’ll have a star-formation laden tree this year!

To create your Milky Way Project bauble, you need to cut-out each of the four images and then fold each one in half (as below).

Using a glue stick, stick the four sections together to form the bauble – remembering to insert a bit of ribbon, paper or string to hang the decoration onto the tree.

Printing the images onto good quality paper or card will produce a better result – but there you have it: citizen science on your Christmas tree!

There Is No Right and Wrong

Continuing this series of posts, answering questions from Milky Way Talk, MWP user UncleClover writes:

I’m a very fast learner, but only if there’s some sort of feedback going on letting me know what I’m doing right and what I’m doing wrong. Once an image that we notated has been processed by a professional, is there any way for us to look it up and find out how accurate or inaccurate our notations were?

Feedback wouldn’t even need to necessarily be an extra step, just having access to your own prior notations and being able to compare them to the “final conclusions” of the professional analysis would be useful.

And in a similar vein, user katieofoz writes:

I was just wondering about a few thing that someone here might be able to answer.

  • Im assuming the data collected for each image is compiled and if a similar marking shows up a certain number of times someone (with actual qualifications) looks at the image and classifies it? Is this right?
  • From the data collected is there anything that looks at how often a person is correct in their markings? Like some sort of way of ranking the user based on their observations?
  • What is done with the compiled data afterwards? Is it based off the average of observations or are areas looked at by qualified individuals to map it more accurately?

An important thing I learnt during my PhD is that there’s an awful lot of work involved in research that you really don’t need a PhD for. Or even a degree. Just a pair of eyes will do, and a few fingers. The tasks you’re performing for Milky Way Project are a great example of that. I may well have a PhD, but I’m no better than any of our users at finding or drawing bubbles. So really, we’re all experts in this project, and as long as you’re genuinely drawing what you believe is a bubble, or a knotty thing, or a dark cloud, there is no “right” and “wrong”.

To be clear, all we’re doing in the science team is providing you with the dataset, and then gathering up all the drawings of all the users and merging all that information into a consistent catalog of objects. We implement a few quality control measures, for example we consider a new user’s first few drawings to be practice drawings and don’t enter those into our dataset – as UncleClover says, there is a learning process.

We make no judgment on whether a drawing is “right” or “wrong”, and we don’t process individual images or users’ drawings. Once you’ve had a little practice, every click counts. All the clicks go into a (giant!) database, and a computer program written by Robert Simpson analyses all the data.

This program essentially scans the whole are of the sky covered by our images and locates clusters of ellipses that users have drawn (you can see an example image with all the various drawings made my volunteers, above). Where we find more than a given number in a small region, we mark this as a bubble. The bubble’s properties that go into the catalog are calculated from averages of the individual users’ classifications – as katieofoz rightly suggests. So whether a bubble you drew ends up in the catalog really just depends on whether lots of other people agreed with you. Given that there’s no real “right” or “wrong” in MWP, we don’t rank the users. It’s not a competition! But our processing algorithm does allow the classifications by experienced users to count more heavily than those of newbies.

Rob wrote more about the procedure earlier on this blog, and of course this will all be described in a lot of detail in the forthcoming paper.

If you haven’t done so already and you’re interested in knowing more about the infrared bubbles in the interstellar medium, I’d invite you to read the original bubbles papers of 2006 and 2007, written by our science team members Ed Churchwell (U Wisconsin-Madison), Matt Povich (Penn State), Bob Benjamin (U Wisconsin-Whitewater), Barbara Whitney (U Wisconsin/Space Science Institute) and their collaborators. This paper is packed with information on the Spitzer surveys we’ve taken our data from,the difficulties in picking out bubbles and what the bubbles might physically represent. The references are below, and the paper should be available via the ADS link.

Churchwell, E., Povich, M., Allen, D., Taylor, M., Meade, M., Babler, B., Indebetouw, R., Watson, C., Whitney, B., Wolfire, M., Bania, T., Benjamin, R., Clemens, D., Cohen, M., Cyganowski, C., Jackson, J., Kobulnicky, H., Mathis, J., Mercer, E., Stolovy, S., Uzpen, B., Watson, D., & Wolff, M. (2006). The Bubbling Galactic Disk The Astrophysical Journal, 649 (2), 759-778 DOI: 10.1086/507015 [ADS]

Churchwell, E., Watson, D., Povich, M., Taylor, M., Babler, B., Meade, M., Benjamin, R., Indebetouw, R., & Whitney, B. (2007). The Bubbling Galactic Disk. II. The Inner 20o The Astrophysical Journal, 670 (1), 428-441 DOI: 10.1086/521646 [ADS]

Zooming and Drawing

Continuing this series of posts, answering questions from Milky Way Talk, here’s one from MWP user broomrider1970, who asked about a zoom option for the images. In fact there’s a whole thread about this on Talk.

When we first started planning the Milky Way Project (MWP) and began testing the interface, we actually had quite a lengthy discussion about a zoom option. In fact, digging through my email, it was my very first question to the developers. As it turns out, adding the zoom option is first of all quite challenging technically. Secondly, and more importantly, giving users the ability to zoom in on images gives us an extra level of uncertainty when we’re trying to process the classifications. By keeping the image static we know for sure that all the users saw the same image in the same way, and we know exactly what the minimum and maximum bubbles sizes are for each image. So it was really an issue of ensuring consistency in the classifications.

Next up: user chairstar asked:

Since I’ve found so many areas of interest – not just IDRC’s but other things like green knots, which do not have a round or square shape, I’d like to see if there is a way of allowing us to ACTUALLY drawing “lines” around irregularly shaped areas, as opposed to being constrained to the classic square and round shape that we are to use now.

Perhaps incorporating a drawing software, allowing free-hand lines could be put in.

Again, this is something we thought about. Particularly for the infrared dark clouds (IRDCs), which tend to have complex filamentary shapes, we wanted to have some kind of polygon- or freehand-drawing tool. But as with the zoom option, having freehand drawings as classifications makes it very challenging for us to merge all these drawings into a consistent catalog of objects. I’m also not sure how we would codify the information captured in freehand drawings in an easily accessible format.

In addition, for the specific case of IRDCs, it wasn’t clear that this would give us better results than an automatic detection algorithm. Several existing IRDC catalogs detected dark clouds with algorithms, and these actually do quite a good job. Not wasting people’s time on tasks that are done just as well by a computer is a core principle of the Zooniverse’s citizen science philosophy.