The images from five Brazilian amateur astronomers have captured Hubble-level details in galaxies, laying the ground for future work in understanding their histories. Want to join the fun?

Centaurus A
Centaurus A (NGC 5128), a galaxy with a violent past

In a promising proof-of-concept, a professional astronomer has teamed up with five amateurs to capture the echoes of long-ago mergers ringing nearby galaxies.

Duilia de Mello (Catholic University of America and NASA Goddard) is leading the Deep Images of Mergers (DIM) project to capture the faint shells of stars that lie on the outskirts of a class of galaxies thought to have had a merger in their past.

Simulations show that when a large galaxy collides with one 10 or 100 times less massive, it tears the smaller one apart. The stars themselves survive, though, even if their galaxy doesn’t. Their orbits disrupted, they slosh around the larger galaxy, ending up in shells that line its periphery. Following the merger, the galaxies are thought to become lenticular, a state of transition between the more typical spiral and elliptical shapes.

To test this idea, de Mello, who is from Brazil herself, engaged with five Brazilian amateurs — Marcelo Wagner Silva Domingues, Cristóvão Jacques Lage de Faria, João Antônio Mattei, Eduardo de Jesus Oliveira, and Sergio José Gonçalves da Silva — to observe nearby lenticular galaxies, including Centaurus A and Arp 230. Their telescopes include two Ritchey–Chrétiens, an 8-inch and a 12-inch, a Celestron 11-inch Schmidt-Cassegrain, a 450mm reflector, and an APM 140 mm refractor.  The observers take observations using a luminance filter, a clear filter that lets the full visual band, from 400 to 700 nanometers, pass through.

Centaurus A and shells
This animation shows an image of Centaurus A from the DIM project. Analysis of the image reveals shells of stars, both previously known (yellow) and those detected by the DIM project (red).
Diulia de Mello / DIM Team

Centaurus A was the proof-of-concept: The team knew that the 4-meter Victor Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile had taken deep observations of this dusty edge-on galaxy, which would provide a point of comparison with the amateurs’ images. With more than 40 hours of integration time using four amateur optics, the team was able to reveal the stellar shells previous teams had seen with the professional telescope.

Arp 230
This Hubble image showcases the beautiful lenticular galaxy Arp 230, surrounded by rings from a past merger.
ESA / Hubble & NASA

The team then turned to Arp 230, a galaxy five times farther away than Cen A. Serendipitously, this galaxy turned out to have Hubble observations, but that’s not why the team selected it. In addition to being lenticular, this galaxy also has large amounts of hydrogen gas thrown to the periphery, probably knocked loose during a long-ago merger. With just 10 hours of integration, the team reached a magnitude of 21.5, revealing four shells that Hubble also detected.

“We have hints of another outer shell not seen in the Hubble image, but it needs to be confirmed with deeper images,” de Mello says. “Unfortunately, the weather in Brazil has been really bad and we were not able to add many more hours yet.”

Stellar shells around Arp 230
These reverse black-and-white images show four known stellar shells (yellow) ringing Arp 230. The DIM team sees hints of another ring (orange dashed lines), which Hubble didn't detect, but additional data is needed to confirm it's really there.
Diulia de Mello / DIM team

While the team is waiting for additional data before they publish these results, de Mello presented the proof-of-concept at the January meeting of the American Astronomical Society. These preliminary results already show that amateur observers with good equipment can reach impressively faint magnitudes and reveal Hubble-level detail in the dim outskirts of these galaxies.

“The collaboration is really hands-on and dynamic,” de Mello says. “I give them a list of candidates and they get themselves organized to observe.” The group meets regularly over Zoom to go over the analysis, she adds, and they use WhatsApp to keep everyone up to date.

Besides adding more data to the Arp 230 analysis, De Mello is also looking to expand the number of galaxies — and the team. Check out the group's Facebook page, and if you're interested in contributing, sign up to join them via this online form.



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