Astronomers have many tools to study the cosmos: telescopes, satellites, interplanetary spacecraft, etc. The humble human eye is also an essential part of this toolkit, as it can often spot patterns or aberrations that algorithms miss. And the examining power of our vision has been enhanced recently by virtual reality (VR) as well as thousands of eyes working in tandem through the crowdsourcing power of the internet.
Researchers at NASA’s Goddard Space Flight Center recently announced the discovery of 10 stars surrounded by dusty debris disks – swirling masses of gas, dust and rock left over from the early stages of planet formation. This result, made possible by virtual reality and the help of citizen scientists, was recently published in the Astrophysical Journal. The results could help astronomers piece together a timeline for how planetary systems were built.
The debris disks encompass various stages of planet formation, including early eras in which worlds are still embedded in the detritus of the disorderly and chaotic processes of their birth. Although astronomers have managed to see a few directly, most of these young planets are beyond the reach of current telescopes. Creating a planetary system takes millions of years, so each disk of debris observers see is just a brief snapshot of a moment in the life of that system. To uncover the full story, astronomers search for numerous disc-crowned planetary systems at different stages of evolution, gathering multiple snapshots to piece together in time.
To hunt for debris disks, observers typically start by looking for stars that appear particularly bright in the infrared; this anomalous brightness usually comes from excess dust heated by starlight in a disk around a star. NASA’s Wide-Field Infrared Survey Explorer (WISE) infrared telescope surveyed the entire sky, creating what, in some ways, is the most comprehensive catalog of stellar infrared measurements to date. With tens of thousands of data points to analyze and many debris disks likely hidden in the WISE catalog, what is a scientist to do?
“It’s a great example of how much of modern astronomy involves searching huge datasets for the proverbial needle in the haystack,” says Wesleyan University astronomer Meredith Hughes. , who did not participate in the study. “Even with machine learning algorithms, it’s still difficult to train computers to do this complex job of identifying noisy patterns and detecting subtle deviations from expectations, which is where the collective intelligence of citizen science.”
A project called Disk Detective has trained citizen scientists — ordinary people who want to help with research in their spare time — to examine WISE images and compare them to those from other astronomical surveys, such as the SkyMapper Southern Sky Survey, the Pan-STARRS and the Two Micron All Sky Survey (2MASS), with the aim of confirming the presence of discs around each candidate star. Since the project began in 2014, citizen scientists have found more than 40,000 disks, or 40,000 snapshots of the history of planet formation.
To put them in a timeline, however, astronomers must figure out where each snapshot belongs. In other words, scientists need to know the age of each star and its debris disk. “When we know the ages of stars and planets, we can put them in a sequence, from baby to teenager to adult, if you want,” says Marc Kuchner, NASA astrophysicist and co-author of the new study. “It allows us to understand how they form and evolve.”
Determining the age of a star with substantial accuracy is a notoriously tricky problem in astronomy. One solution is to associate a star with his brothers and sisters, in an association called a moving group. Stars often form in clusters from a giant gas cloud, but many of these once-close stellar families split as they age, their individual members spreading across the Milky Way. By carefully measuring the locations and velocities of stars, researchers can determine which stars are displaying the telltale motions that, when traced back, reveal that they were born collectively at the same time and place. Once astronomers know that the stars in a group are related, it is simple to calculate their age based on established knowledge of star growth and evolution.
Finding new moving group members is not easy. To do this, astronomers traditionally rely on analyzing pre-existing lists of moving group stars, flagging potential new members through sophisticated mathematical models. The team behind the new project wanted to try something different and more visceral: they used a VR program to zoom around the stars and get a clearer three-dimensional perspective on how things move.
“I thought I was going to scare [NASA’s VR scientists] far when I said I wanted to visualize the positions and velocities of four million stars,” says Kuchner. “But they didn’t flinch!” To create this virtual stellar cornucopia, the team used data from Gaia, a European Space Agency satellite that provides the best available measurements for the positions and velocities of stars in our galaxy. The resulting VR simulation also served as a sort of time machine. Knowing how fast and in what direction a star was moving allowed Kuchner and his colleagues to track its movement back and forth in time.
While a visiting scientist at NASA, the study’s lead author, Susan Higashio, strapped on a VR headset to fly over the simulation’s millions of stars. She looked at where the stars with disks were in relation to known moving clusters and extrapolated the forward and backward motions of the stars in time to test their potential associations. “It was so exciting when the four million stars showed up in VR, but it was kind of dizzying when they all started swirling around me,” she recalls. “It was a really fun and interactive way to do science.”
Higashio traced 10 of Disk Detective’s debris disks back to their mobile group families. The team then found the estimated age of these discs, which ranged from 18 million to 133 million years old. All were extremely young, compared to our home solar system, which is around 4.5 billion years old. Researchers have also identified a brand new mobile cluster called Smethells 165, after its brightest star. “Every time we find a new mobile group, it’s a new batch of stars whose age we know more precisely,” says Kuchner.
Astronomers have also found a strange and extreme debris disk around a star dubbed J0925 that doesn’t quite fit their projected timeline for planet formation. It is much brighter in the infrared, which means it contains more dust than expected for a star of its age. As the debris disks age, some of their dust winds up around the star or is carried away by stellar winds. J0925, however, appears to have received a new delivery of hot dust, possibly from a recent collision between two protoplanets. Hughes highlights this star as the most interesting object discovered in the study. “Extreme debris disks are still a bit of a mystery, but they’re likely similar to what our solar system would have looked like during the giant impact that formed Earth’s moon.”
Disk Detective’s citizen science work is still ongoing, now upgraded to use Gaia’s newest batch of data. The team hopes to identify even more mobile band members and new records with their unique VR method. Lisa Stiller, one of the study’s many citizen scientist co-authors, offers encouragement to potential volunteers. “Feel free to participate in a citizen science project,” she says. “Your help will be needed no matter what form you choose or how much time you choose to devote to it.”
Anyone with an internet connection can still join the Disk Detective project, no experience is required. “More than 30,000 citizen scientists have contributed,” says Kuchner. “Disk Detectives are still going through hundreds of thousands of WISE images. We still need your help.”