It’s not too often that a high school student-turned undergraduate gets three galaxies named after him, especially ones that are breaking the rules of star formation. Julian Shapiro, currently an astrophysics student at the University of California, Berkeley, found strange dwarf galaxies in the vicinity of the large spiral M101 while doing research into their star formation rates as a high school student. They’re now known as Shapiro I, II, and III. In the process, he’s become an inspiration to other students who might be interested in astrophysical research.
“I envision my work serving as inspiration for young people aspiring to pursue research in astrophysics,” said Shapiro. “Often, school curriculums provide limited introductions to astronomy, and it is difficult for students to find mentorship and build experience in the field. My paper demonstrates that public archival telescope data is a critical tool for new discoveries in our understanding of cosmology and how our universe evolved, and that young astronomers are capable of uncovering these findings.”
At Berkeley, Shapiro is part of a research group led by astrophysicist Alexei Filippenko, working on cosmological measurements that have resulted in differing definitions of the Hubble Constant. He will also be doing follow-up work on his Shapiro galaxies as part of his undergraduate experience. “Julian conducted some remarkably sophisticated research while still in high school, which is highly unusual and was recognized with the prestigious Davidson Fellowship,” said Filippenko. “I feel very fortunate that he chose UC Berkeley for his undergraduate studies in astrophysics, and especially that he decided to join my research team.”
Diving into Dwarf Galaxies
So, why study dwarf galaxies? It turns out, they’re an important part of galaxy evolution in the Universe. Dwarf galaxies are, as you might expect, small galaxies with as few as a thousand stars all the way up to a few billion stars. They come in different flavors and shapes, ranging from dwarf ellipticals and spheroidals to irregularly shaped ones and tiny spirals. Astronomers suggest that they form as part of the galaxy collision process, when material from two larger ones gets spun out to intergalactic space and aggregates to become a dwarf galaxy.
“Dwarf galaxies exist both in isolation and as satellites around larger galaxies like our own Milky Way,” said Shapiro, who just published a paper about his work in The Astrophysical Journal. “In isolation, these galaxies are expected to be actively forming stars, as there are no larger galaxies to strip their star-forming gas, but the galaxies I discovered break this rule. My paper argues that they may be among the first resolved ‘backsplash’ galaxy candidates, or galaxies that once passed close to a large neighbor, whose pressure removed their gas, before being flung outward.”
These backsplash galaxies should be fairly common in the Universe, but finding them in our local neighborhood has been difficult. They’re predicted by the lambda-cold dark matter model of cosmology, which says they shouldn’t be very rare. Yet, here are the Shapiro three, not engaging in much star formation. The big question is: why aren’t they creating more stars? Shapiro used simulations to figure out that something external to those three galaxies must have had an influence on them, which resulted in the low star-formation rate.
Figuring Out the Details
Galaxies like the Shapiro Three exist in relatively isolated splendor in regions that are rich in star-forming gas. Any dwarf galaxies that have stopped creating stars (astronomers call it “quenching”) exist in more densely populated galactic environments or are circling larger host galaxies. Interactions between the dwarfs and their larger siblings “steal” the gases needed for star birth. That explains why those close to other galaxies aren’t forming many stars.
These panels show three of the Milky Way’s ultra-faint dwarf galaxies. Such galaxies are important probes for conditions in the early Universe, even though they (like the Shapiro galaxies) exist in the more “recent” Universe. Image Credit: DECaLS/DESI Legacy Imaging Surveys/LBNL/DOE & KPNO/CTIO/NOIRLab/NSF/AURA
The three dwarf galaxies Shapiro discovered present a puzzle: they are both isolated and quenched. So, how could this be? Shapiro’s explanation, based on his work with simulations and observations, invokes a galactic dance between the dwarfs and some larger galaxy, perhaps M101. He suggested that the Shapiro Three plowed through the gravitational well of Messier 101, known as the Pinwheel Galaxy. If that happened, then the shock of the collisions and interactions stripped away their star-forming gas. Not only that, but the interaction hurled them into intergalactic space. One of the dwarfs, Shapiro Dwarf Galaxy II, lies close enough to spiral galaxy NGC 5585 that it might be a satellite of that galaxy rather than a participant in an interaction with M101.
Shapiro spent a great deal of time estimating the distances to determine whether the dwarf galaxies were truly isolated. If they are, then the idea that they were shaped and quenched by galactic interactions should help find other, similar-type objects. Shapiro’s paper focuses on how to determine the frequency of these galaxies based on future observations using next-generation observatories. “Building the foundational knowledge necessary to detect the galaxies, develop modeling and analysis code, and analyze the results in comparison to our cosmological model was a challenge,” he said. “I was fortunate that many of the leading journals in the field are free to access, which helped me gain an understanding of the necessary techniques and background.”
He hopes that follow-up measurements from high-resolution space telescopes will definitively map the exact positions of the dwarf galaxies, in order to determine if they could be backsplash galaxies. In addition, Shapiro expects that the new Vera C. Rubin Observatory will reveal many potential backsplash galaxies like the ones he uncovered.
Julian Shapiro poses in front of the Richard Treffers Telescope on the rooftop of UC Berkeley’s Campbell Hall. Credit: Shannon Kelli
For More Information
A Berkeley Undergraduate’s Research Leads to an Astronomical First
Discovery of Isolated, Quenched Candidate Backsplash Dwarf Galaxies Near M101