An amateur astronomer has discovered a previously unknown galaxy using a home telescope and camera. The object has been confirmed with one of the world's largest telescopes, and adds support to the most popular model of galaxy formation.
Astronomy is famous as a field where amateurs still do work that significantly adds to scientific knowledge. However, most contributions are in areas where the sky is changing fast, such as the discovery of new comets before giant telescopes happen to look in the right location. A slowly evolving galaxy doesn't fit that picture.
Nevertheless, when Michael Sidonio took a photograph of the well-known galaxy NGC 253 he picked up something nearby that had never been noticed before. Sidonio, who is security manager at the Australian Capital Territory's Legislative Assembly in his day job, was using a 30-centimeter (12-inch) diameter telescope – large for an amateur but hardly professional size – which he keeps on a farm 10 kilometers (6 miles) from the outskirts of Canberra.
NGC 253 has been photographed many times, but Sidonio told IFLScience that he took a much wider angle image than is usually done, taking advantage of his telescope's unusually short focal length for a mirror that size. The image was a finalist in the Royal Observatory Greenwich’s 2013 astronomy photograph of the year award, bringing it to the attention of professional astronomers studying dwarf galaxies. The outcome of their collaboration will be published in Monthly Notices of the Royal Astronomical Society (preprint on arXiv).
NGC 253, also known as the “Silver Dollar galaxy” was discovered by Caroline Herschel in 1783, and is popular with southern hemisphere astronomers. At 11.5 million light-years away it is one of the closer large galaxies to our own, and is undergoing intense star formation.
Fellow amateur, Alessandro Maggi also photographed the small galaxy next to NGC 253 using an 18-centimeter (7-inch) telescope. The paper's authors write: “In both cases, the pixel scale was coarse and it was not clear if the elongated feature was real or an artifact or reflection as often present in amateur images.” Sidonio told IFLScience the paper's other authors contacted him to request the original to improve their confidence that the finding was real.
After confirming the galaxy's presence with CHART32, an 80-centimeter (31-inch) telescope run by a group of amateurs, first author Dr. Aaron Romanowsky of San José State University, secured time on the giant Chilean 8.2-meter (27-foot) Subaru Telescope for detailed study. The authors named the galaxy NGC 253-dw2 and say it has “an old metal-poor stellar population” and shows signs of being disrupted by its larger neighbor.
Sidonio's image with NGC 253-dw2 circled, both in negative and real color. Credit: Michael Sidonio.
Thousands of galaxies are discovered each year, but a shortage of small galaxies in the local Universe has cast doubt on the “hierarchical model”, under which large galaxies form from smaller ones. From studying the way NGC 253-dw2 is being destroyed by its larger neighbor the authors conclude: “Our observations support the hierarchical paradigm.”
In words that should encourage every recipient of a Christmas telescope, as the paper notes: “We also note the continued efficacy of small telescopes for making big discoveries.”
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