Twelve undergraduates and one very patient lecturer.
A faint cloud of glowing gas, too dim to be seen with the naked eye and missing from every published catalogue, has been identified by a group of undergraduate physics students using a modest telescope on the roof of Calder University’s science block.
The object, a small emission nebula in the constellation of the Swan, was first noticed in images taken over seventeen clear nights last winter. The students’ paper describing it has now been accepted by a peer-reviewed astronomy journal, an unusual achievement for a group whose members are mostly in their second year of study.
The discovery came out of an optional observing module run by Dr Alasdair Brennock, a senior lecturer in astrophysics, who has spent eight years persuading the university to let students use the 40-centimetre reflector for long-exposure imaging rather than occasional open evenings. Twelve students signed up last October. None of them, he said, expected to find anything.
Hours of exposure, one smudge
The project was designed as an exercise in patience. Each student took responsibility for a patch of sky and was asked to collect as many hours of exposure as possible through a narrow filter that isolates the red light emitted by hydrogen gas. Clear nights over Calder are rare in winter, and the group shared a rota that sometimes had students climbing to the roof at three in the morning when a gap opened in the clouds. By February, second-year student Freya Lindahl had stacked nearly 26 hours of exposure on her assigned field. When she processed the images, a faint, roughly circular glow appeared near a pair of bright stars. She assumed it was a reflection from inside the telescope.
“I spent two weeks trying to make it go away,” said Freya Lindahl. “I changed the processing, I checked the flat frames, I took the camera off and put it back on. It just kept being there. Eventually I showed it to Dr Brennock and said, I think I’ve broken something.”
Dr Brennock’s first reaction, he admits, was the same. Only after the group had re-imaged the field on six more nights, rotated the camera to rule out internal reflections and compared their data with archive images from several professional surveys did he begin to believe it was real. Older survey images, re-examined with the coordinates in hand, show the faintest trace of the same structure, but it had never been flagged.
What the students found
The nebula is estimated to be about four light years across and is thought to be a shell of gas puffed off by an ageing star near its centre, a type of object known as a planetary nebula. Its glow in hydrogen and, weakly, in oxygen light fits that interpretation. If confirmed, its distance would place it roughly 4,500 light years from Earth.
To strengthen the case, the students arranged for spectra to be taken by a professional observatory abroad, which granted them two hours of time through a scheme that supports student-led research. The spectra confirmed emission lines consistent with a planetary nebula and showed the gas expanding at around 25 kilometres per second. All twelve students are listed as co-authors, alongside Dr Brennock. Under the journal’s naming conventions the nebula will carry a catalogue number, but the group has informally christened it “the Roof”, after the place where most of their nights were spent.
Professor Mariam Esterhuizen, head of the university’s physics department, said the find showed what students could achieve when given time on real equipment rather than pre-packaged exercises. “The textbooks tell you that discovery requires enormous instruments. Sometimes it requires a small telescope, a lot of nights, and a student who refuses to accept that a smudge is a mistake,” she said.
Back on the roof
The observing module has more than doubled in size this year, with 27 students enrolled, and the university has agreed to fund a second camera. Dr Brennock is now hoping the success will help make the case for a small dark-sky observing station on Harrow Moor, away from the city’s light. In the meantime the students are planning further imaging this winter to map fainter outer layers of the nebula. Ms Lindahl, now in her third year, says she has changed her plans and intends to apply for a doctorate in astronomy. “I used to think discoveries were made by other people,” she said. “It turns out other people are just whoever is still awake.”
