Slim and beautiful galaxies, too good to be true.

[HysteryDiagnosis]

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Then, in 2004, Kormendy teamed up with Ralf Bender of the Max Planck Institute for Extraterrestrial Physics in Munich, Germany. Their groups started to examine detailed images of large nearby spiral galaxies taken by the Hubble Space Telescope, backing them up with spectral observations from the University of Texas's Hobby-Eberly Telescope. The results, published in November last year, were something of a shock. Of 19 large nearby spirals, at least 11 seemed to have no bulge, indicating that violent mergers didn't feature in their past. Among them were the seemingly exemplary Pinwheel galaxy - and the Milky Way (The Astrophysical Journal, vol 723, p 54).

What these galaxies do have is a bright central concentration of stars all crowded together. To a casual observer it looks like a bulge, but the orderly trajectory of the stars, plus areas of active star formation characteristic of quietly rotating discs, indicate that these stellar swarms do not in fact protrude from the galaxy's plane. It is a nicety that is easy to overlook if we don't have the luck of seeing a galaxy edge-on. "For many decades, they were misidentified as classical bulges," says Kormendy.

And this huge number of slimline, pristine spirals has morphed into a big problem for the hierarchical picture. To get as large as they are, they must have merged, yet "we don't know how to prevent bulge formation when galaxies grow big via mergers", says Kormendy. Jim Peebles, a cosmologist at Princeton University, agrees. "It is wildly unexpected in the standard model," he says.

It's not the only odd thing about these galaxies, either. Twenty years ago, Kormendy was among the first to propose that supermassive black holes play a significant part in galaxy evolution. We think that these black holes exist at the heart of most galaxies because matter near their cores seems to be whirling around a vastly dense agglomeration of mass. In the 1990s, Kormendy and others noted that bigger bulges tend to go hand-in-hand with bigger black holes, suggesting that the two develop in tandem.