Tag Archives: Dark Clouds

We’re Not Cloud Painters

A current hot topic in star-formation science is the study of Infrared Dark Clouds (IRDCs). These are really dense molecular clouds that appear dark even in infrared surveys.

For a while, we hoped that Project IX would be our avenue to exploring IRDCs. However, as you’ll see in this blog post, not every idea become a reality at the Zooniverse – for a good reason. Here’s the story of the IRDC project that never was.

IRDC-Example

A Bit About IRDCs

IRDCs appear throughout images from far-infrared surveys – there’s a lovely example in the image above. It was not initially known what lay within them. Closer study revealed that they have sizes and masses similar to high-mass star forming molecular clouds. Similarly, the dense cores within IRDCs appear to match the sizes and masses of high-mass prestellar cores – the direct progenitors of stars. IRDCs also seem to be located along the spiral arms of our Galaxy, which is where star formation mostly occurs (Jackson et al, 2008, see image below). A few IRDCs even show evidence that they contain young proto-clusters of stars. In short, evidence seems to suggest that early phase high-mass star formation is occurring within IRDCs.

High-mass star formation is another hot topic in astrophysics. It is not fully understood how stars several or hundreds of times bigger than the Sun form. We know that they do and that they can get really big – but compared to the process of low-mass star formation their origins are a bit of a mystery. IRDCs may hold some answers.

Jackson-2008-IRDC-Image

It has been established that there are upward of 10,000 IRDCs visible to us here on Earth (Simon et al. 2006a). For each of these it would be useful to know their size, shape and location. The Spitzer Space Telescope’s Galactic Legacy Midplane Infrared Survey Extraordinaire (GLIMPSE) highlights many of these often beautiful dark clouds and the data is available for use. The question is how do you visually classify this many dark clouds in such a large dataset?

Project IX

This started to sound to me like a potential citizen science problem. Lots of objects to be found, a task that computers find difficult, and a large dataset. We got really excited here at Zooniverse HQ, and began to concoct an idea that would see tens of thousands of volunteers literally painting clouds in space. I developed a prototype HTML5 interface that allowed someone to draw around IRDCs in GLIMPSE data (se image below). Sadly, our enthusiasm wasn’t to last.

HTML5-Test001

We had a prototype interface and we had lots of GLIMPSE data – but Chris was worried. I kept bringing him a new developments and he’d be interested, excited but also cautious. So we sat down to really get to the bottom of this idea. Imagine 1,000 people were to draw around the same IRDC in an image. Each person looks at the image and decides in their own mind where they would say the border between the dark cloud and the surrounding bright emission is. They then draw around the cloud, fairly imperfectly, following roughly that ratio of dark-to-light.

Translating this into a different vocabulary: each person decides on a contrast ratio and tries to follow a fixed-contrast contour around the dense region in the image. We then average those contours to get the group’s decision on the best contrast ratio to use.

Have you spotted the problem? The average contrast ratio achieved by this method is no more right or wrong than any other value. You may as well have taken a computer and told it to draw a contour at a specified contrast ratio across the whole Galaxy. You can derive that ratio via some meaningful number that can be calculated from the data – maybe the extinction or the signal-to-noise. The 2006 paper that identified the Galaxy’s 10,000+ IRDCs already did this – instead of improving upon the existing study, we would have ended up replicating it, only in a slightly different way. We compared our own visually identified clouds to those drawn out by the Simon et al., 2006 algorithm and found the results were very similar. As such the cloud painting project was more-or-less concluded there and then.

Moving On

The Zooniverse has policies on what makes a good citizen science project. These guidelines have been produced following the lessons of Galaxy Zoo and other projects. Chris wrote up a blog post about this the other day. Our one unbreakable rule is that if we ask the public to collaborate on a project, their efforts must produce a meaningful result. We must never waste people’s time.

I’ll be honest, I was a bit gutted. Cloud painting would be possible and it would yield a reasonable result. It would even be fun! However it wouldn’t add anything scientifically useful to what we know about the Galaxy’s IRDCs. Just because a problem can be crowd-sourced doesn’t mean it should be.

Luckily for Project IX, there is a lot more to see in the GLIMPSE data than just IRDCs. So we leave the dark clouds to the machines and in our next post we’ll finally talk about the great science that we can achieve.

If you want to learn more about IRDCs there are lots of papers and talks on the subject out there on the web. If you’d like to read some of the papers here’s a potted history of IRDCs – Simon et al. 2006aRathborne et al., 2006 and 2007Simon et al., 2006bJackson et al, 2008and Chambers et al., 2009.

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Introduction

Star formation is one of the most important processes at work in the cosmos. The atoms that make up our planet and ourselves were made in the centres of stars, billions of year ago. To study star formation is to begin to understand the origin and make-up of the Galaxy and the Universe at large.

The mass distribution of stars and the rate at which they are born determines the nature and evolution of galaxies, such as our own Milky Way Galaxy. To understand many aspects of galaxy evolution, planet formation and cosmology, an understanding of star formation is required. It is one of the most fundamental mechanisms at work in the Universe.

Here at Zooniverse HQ we’ve been looking at how to get involved with the study of star formation for a while now. This is, in no small part, due to the fact that three of us at Zooniverse HQ have a background in star formation research. Chris Lintott, Arfon Smith and myself have all worked in this field and thus have been keen to make this project a reality for some time.

Project 9 is going to be the first Zooniverse contribution to the field of star formation. Project 9 is also going to be the first Zooniverse project to crowd-source more than just the science. We’d like to get opinion and feedback from the Zooniverse community as we develop the project.

800px-Andromeda_galaxy_Ssc2005-20a1

Image Credit: NASA/JPLCaltech/K. Gordon (University of Arizona)

Project 9 will be using data from the Spitzer Space Telescope, one of the most successful science missions ever put in orbit (which took the stunning image of the Andromeda Galaxy seen above). We’ve been working with the people behind the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). We think that you all may be able to help us classify some of the structures seen in this data – but more on that in a future post.

Stars form within dark clouds of gas (predominantly hydrogen and helium) and dust (larger molecules that have collected together into grains). They are dark because they absorb visible light. The dust in these star-forming regions absorbs visible light, and reemits it at infrared wavelengths. The result is that if you want to look for stars in the making, you must look in the infrared. The Earth’s atmosphere absorbs infrared light, so to search for star-forming regions you need to use a space-based infrared telescope – like Spitzer.

eagle

Infrared images of star-forming regions are often beautiful – you can browse a version of the GLIMPSE data via this link. We have been toying with different colour stretches for the GLIMPSE data to use for Project 9. Amongst the plethora of gorgeous images – from just a small part of the sky – I came across a familiar object: the Eagle Nebula (above). I thought this would give you an idea of the sort of images Project 9 will be asking everybody to help dissect and classify.

We’re looking forward to getting this project off the ground and will be blogging shortly with more details.