With the help of citizen scientists, U of M-led research team completes the largest-ever search for ‘clumpy’ galaxies in the modern Universe

Research will help scientists learn how galaxies form and evolve over time

MINNEAPOLIS / ST. PAUL (01/18/2022)—A new study led by University of Minnesota Twin Cities researchers, with the help of more than 14,000 citizen scientists, has come up with the largest-ever count of “clumpy” galaxies in the local Universe. The researchers found that there are significantly fewer clumpy galaxies—or galaxies with dense, star-forming regions—in the modern Universe compared to its early history, and now have a definitive, detailed catalog that they can use to study further topics, such as how galaxies evolve.

The paper has been submitted to the Astrophysical Journal, a peer-reviewed, scientific journal from the American Astronomical Society (AAS).

“We now have the largest sample of human-classified clumpy galaxies that's ever been put together,” said Nico Adams, lead author on the paper and a grad student in the University of Minnesota Twin Cities School of Physics and Astronomy. “What’s exciting is that we can now use that data as an input for machine learning to extend that over a much larger group of galaxies and expand our study even further.”

The data was gathered through the Galaxy Zoo project, which is a part of Zooniverse, an endeavor co-founded at the University of Minnesota and now the world’s largest and most popular people-powered online research platform. 

Volunteer citizen scientists looked at pictures of more than 58,000 galaxies in the “local” or “modern” Universe—which spans a radius of up to one billion light years away from Earth, or the equivalent of looking one billion years into the past—to create a catalog of galaxies with visible “clumps.” Using this data, the University of Minnesota-led team found that the number of clumpy galaxies in the Universe has decreased by about 95 percent in the last eight billion years. 

By looking at images from the Hubble Space Telescope that span over the last 10 billion years of cosmic history, astronomers know that galaxies have progressed from being clumpy to being smooth, or resembling the spiral or elliptical shape many people recognize today. But what they didn’t know was how many galaxies still retain their clumps today.

“The number of clumpy galaxies that we got is way smaller than anyone anticipated. We knew they were rare in the local universe, but how rare they were was a big surprise,” Adams said. “Clumpy galaxies are so poorly understood by us so far, and they represent this huge gap in our knowledge of the Universe. If we ever want to understand how galaxies evolve over time, we need some explanation of how they went from clumpy to smooth, and this catalog is going to help us do that.”

Most studies of clumpy galaxies in the past have focused on galaxies that are farther away, typically five billion light years or more where clumps are more common. However, it’s tough for scientists to study these galaxies in depth because they are so far away. With this new data, Adams said, researchers will be able to look at clumpy galaxies in more detail at a higher resolution, which will help them learn more about galaxy clumps and how the Universe has evolved over time.

In addition to Adams, the research team included researcher Vihang Mehta, Professor Claudia Scarlata, and Professor Lucy Fortson from the Minnesota Institute for Astrophysics at the University of Minnesota Twin Cities; Professor Hugh Dickinson from The Open University, UK; research scientist Sandor Kruk from the European Space Agency; research fellow Brooke Simmons from Lancaster University, UK; and Professor Chris Lintott from the University of Oxford, UK.

The research was funded in part by the National Science Foundation (NSF) and is based upon work funded by NASA.

Read the full paper, entitled “Galaxy Zoo: Clump Scout: Surveying the local Universe for giant, star-forming clumps,” on the arXiv website.