What are yellowballs?
What are yellowballs?
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Yellowballs (YBs) likely represent clouds of gas and dust that are harboring very early stages of star formation. As gravity pulls cold interstellar clouds of gas and dust together, infant stars (protostars) begin heating the surrounding dust and will look like the infrared image to the left in the panel. As protostars develop further, both dust and gas glow in infrared light, creating a roundish object that appears yellow like the middle image. Astronomers think that most YBs contain multiple protostars, protoclusters of protostars! If some of the stars in a protocluster are massive enough, yellowballs will eventually transform into mature "bubbles," and will look like the right image.
Thanks to the efforts of many volunteers involved in The Milky Way Project, our research group knows the location of thousands of YBs. Now, we are interested in measuring the amount of light at different infrared wavelengths from these objects to see what trends emerge.
Stages in the development of a bubble: In these images, blue (3.6 um) primarily highlights stars; green (8 um) highlights complex organic molecules; and red (24 um) highlights warm dust. The color wheel shows the resulting colors when two or more of these wavelengths overlap. Image Credit: NASA/JPL-Caltech
Volunteers were essential to the discovery of yellowballs.
Volunteers were essential to the discovery of yellowballs.
Each circle in the above image represents a yellowball identified by volunteers in the Milky Way Project. This two-color image displays infrared light, where 8 um emission from excited, large organic molecules known as polycyclic aromatic hydrocarbons (PAHs) is assigned a green color and 24 um from warm dust is assigned a red color. Where green and red emission overlaps, a yellow color appears!
In 2010, the Milky Way Project (MWP) became the ninth project launched on the people-powered research platform Zooniverse. The MWP asked volunteer participants to inspect infrared images from very large surveys of the Milky Way that were conducted by the Spitzer Space Telescope in order to identify "bubbles" produced by winds and radiation from massive young star. As volunteers searched for these bubbles, which appear red with green rims in the color scheme used for these images, they became curious about small, roundish, "yellow" objects. We asked the volunteers to start tagging these objects and eventually modified the Milky Way Project to enable volunteers to identify these so-called "yellowballs" (YBs) throughout the Milky Way, so we could figure out what they are. You can read more about the history of the MWP here.
Thanks to the Milky Way Project volunteers who identified more than 6,000 YBs across the Milky Way, we've been able to demonstrate that most of the roughly 500 YBs we've studied so far are associated with very young groups of stars that are forming together. Some of these groups, or protoclusters, contain very young massive stars, but many do not.
More volunteer help is needed for the next steps in understanding yellowballs.
More volunteer help is needed for the next steps in understanding yellowballs.
Measuring the brightness of YBs from infrared images is tricky. The plane of our Galaxy contains a lot of gas and dust that emit infrared light, and YBs are embedded in this extended Galactic gas and dust. We need to separate the YBs from the background infrared emission of the Milky Way. We developed a tool to do this, but we need people to decide how well each YB can be separated from the background of the Milky Way.
There are a LOT of YBs to measure. Having multiple people make measurements at different infrared wavelengths greatly improves the accuracy of the results, and helps us evaluate how well we can reliably measure the brightness of YBs at each wavelength.
We developed the PERYSCOPE Project to partner with introductory astronomy classrooms. We provide an activity that teaches students the basics of photometry and guides them through using a web-based Python tool. Students collect and analyze their own data using this tool, and have the option of donating their photometry results to our project when they are finished. If you are educator interested in using PERYSCOPE in your classroom, please visit the links below.
Want more? Here is a list of yellowball publications and journalism!
Want more? Here is a list of yellowball publications and journalism!
This blog contains links to papers we published in the Astrophysical Journal and an article for kids in the journal Frontiers for Young Minds. We're excited about these results, but there's much work left to be done to answer fundamental questions about how stars form throughout our Milky Way Galaxy!
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