Volunteers using the web-based Milky Way Project
brought star-forming features nicknamed "yellowballs" to the attention
of researchers, who later showed that they are a phase of massive star
formation. Image credit: NASA/JPL-Caltech. › Full image and caption
This series of images show three evolutionary
phases of massive star formation, as pictured in infrared images from
NASA's Spitzer Space Telescope. Image credit: NASA/JPL-Caltech. › Full image and caption
Sometimes it takes a village to find new and unusual objects in
space. Volunteers scanning tens of thousands of starry images from
NASA's Spitzer Space Telescope, using the Web-based Milky Way Project,
recently stumbled upon a new class of curiosities that had gone largely
unrecognized before: yellow balls. The rounded features are not actually
yellow -- they just appear that way in the infrared, color-assigned
Spitzer images.
"The volunteers started chatting about the yellow balls they kept
seeing in the images of our galaxy, and this brought the features to our
attention," said Grace Wolf-Chase of the Adler Planetarium in Chicago. A
colorful, 122-foot (37-meter) Spitzer mosaic of the Milky Way hangs at
the planetarium, showcasing our galaxy's bubbling brew of stars. The
yellow balls in this mosaic appear small but are actually several
hundred to thousands of times the size of our solar system.
"With prompting by the volunteers, we analyzed the yellow balls and
figured out that they are a new way to detect the early stages of
massive star formation," said Charles Kerton of Iowa State University,
Ames. "The simple question of 'Hmm, what's that?' led us to this
discovery." Kerton is lead author, and Wolf-Chase a co-author, of a new
study on the findings in the Astrophysical Journal.
The Milky Way Project is one of many so-called citizen scientist
projects making up the Zooniverse website, which relies on crowdsourcing
to help process scientific data. So far, more than 70 scientific papers
have resulted from volunteers using Zooniverse, four of which are tied
to the Milky Way Project. In 2009, volunteers using a Zooniverse project
called Galaxy Zoo began chatting about unusual objects they dubbed
"green peas." Their efforts led to the discovery of a class of compact
galaxies that churned out extreme numbers of stars.
In the Milky Way Project, volunteers scan through images that Spitzer
took of the thick plane of our galaxy, where newborn stars are igniting
in swaths of dust. The infrared wavelengths detected by Spitzer have
been assigned visible colors we can see with our eyes. In addition to
the yellow balls, there are many green bubbles with red centers,
populating a landscape of swirling gas and dust. These bubbles are the
result of massive newborn stars blowing out cavities in their
surroundings. The green bubble rims are made largely of organic
molecules called polycyclic aromatic hydrocarbons (PAHs), cleared away
by blasts of radiation and winds from the central star. Dust warmed by
the star appears red in the center of the bubbles.
Volunteers have classified more than 5,000 of these green bubbles
using the project's Web-based tools. When they started reporting that
they were finding more reoccurring features in the shape of yellow
balls, the Spitzer researchers took note and even named the features
accordingly. In astronomy and other digital imaging, yellow represents
areas where green and red overlap. So what are these yellow balls?
A thorough analysis by the team led to the conclusion that the yellow
balls precede the green bubble features, representing a phase of star
formation that takes place before the bubbles form.
"The yellow balls are a missing link," said Wolf-Chase, "between the
very young embryonic stars buried in dark filaments and newborn stars
blowing the bubbles."
"If you wind the clock backwards from the bubbles, you get the yellow ball features," said Kerton.
The researchers explained why the yellow balls appear yellow: The
PAHs, which appear green in the Spitzer images, haven't been cleared
away by the winds from massive stars yet, so the green overlaps with the
warm dust, colored red, to make yellow. The yellow balls are compact
because the harsh effects of the massive star have yet to fully expand
into their surroundings.
So far, the volunteers have identified more than 900 of these compact
yellow features. The next step for the researchers is to look at their
distribution. Many appear to be lining the rims of the bubbles, a clue
that perhaps the massive stars are triggering the birth of new stars as
they blow the bubbles, a phenomenon known as triggered star formation.
If the effect is real, the researchers should find that the yellow balls
statistically appear more often with bubble walls.
"These results attest to the importance of citizen scientist
programs," said Wolf-Chase. Kerton added, "There is always the potential
for serendipitous discovery that makes citizen science both exciting
for the participants and useful to the professional astronomer."
NASA's Jet Propulsion Laboratory, Pasadena, California, manages the
Spitzer Space Telescope mission for NASA's Science Mission Directorate,
Washington. Science operations are conducted at the Spitzer Science
Center at the California Institute of Technology in Pasadena. Spacecraft
operations are based at Lockheed Martin Space Systems Company,
Littleton, Colorado. Data are archived at the Infrared Science Archive
housed at the Infrared Processing and Analysis Center at Caltech.
Caltech manages JPL for NASA.
For more information about Spitzer, visit: http://spitzer.caltech.edu and http://www.nasa.gov/spitzer
Media Contact
Whitney Clavin
Jet Propulsion Laboratory, Pasadena, California
818-354-4673
Email: whitney.clavin@jpl.nasa.gov
