The Pursuit of Serendipity

Whenever I hear the word ‘serendipity,’ I think of my old mentor Norman Eliason, professor of medieval studies at UNC-Chapel Hill. During my years of grad work, Dr. Eliason passed along habits of precision and an eye for detail that I’ve tried, not always successfully, to emulate. One day when he asked about my work habits, I told him that I preferred to work outside the library, checking out books I needed or making copies of relevant journal articles.

I can still see him nodding slowly in his office chair, cigarette protruding from his hand, and I knew I’d said the wrong thing. “You need to be among the books,” he said. “Use your free time to look around and you’ll run into things in the stacks you never knew were there.” I took his advice and he was right. Serendipity –chance discovery, usually when looking for something else — worked. At least, it always has for me, but you have to put yourself in a place where discoveries are likely to be made.

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Image: Serendipitous discoveries combine luck (or chance), preparedness and aim. Conventional school science is usually concentrated on the preparedness, aim plane and totally new things are found on the preparedness, luck plane. There is usually, however, some aim to the observations, which is why I have tried through shading to make the region have volume. Credit (image and caption): A.C. Fabian.

‘Chance or unplanned discovery’ is how Andrew Fabian (University of Cambridge) defines serendipity, but I always add in a notion of good fortune. To me, serendipity means not only making an unexpected find, but making one that materially advances an investigation. Fabian probably wouldn’t disagree, based on the recent paper he wrote on the subject of serendipity in astronomy. Consider:

In contrast with school laboratory science where the aim is to plan and carry out an experiment in controlled conditions, in general astronomers cannot do this and must rely on finding something or a situation which suits. Often, the possibilities afforded by a phenomenon are only appreciated later, after the surprise of the discovery has worn off.

Fabian also quotes Pasteur’s famous “Chance favors the prepared mind.” In any case, we find by looking at examples of serendipity in astronomy that such discoveries often push our thinking into new areas. Fabian also notes the tension inherent in this process, contrasting a ‘fishing expedition’ against the tight methodology that science prefers. This is probably because serendipity seems entirely random, but its history of discovery is robust.

Some cases:

  • Jocelyn Bell and team were looking for so-called ‘radio stars’ in the late 1960s and ran into 1.3-second pulses that led to the discovery of pulsars. Interestingly, earlier data also showed these pulses but were not analyzed sufficiently to reveal them.
  • Gamma-ray bursts (GRBs) were discovered by US military satellites in the 1960s engaged in surveillance of Soviet military activity.
  • A ‘double quasar’ discovered in 1979 turned out to be the gravitationally-lensed image of the same background object. The team investigating the image were making routine quasar measurements of a large number of quasars. Again, images like this one, and many later lensed objects, had been seen and published but not previously noticed as double images, nor their nature understood.

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Image: A foreground galactic cluser whose total mass is gravitationally bending the light from distant galaxies into many arcs. How many such images were catalogued before gravitational lensing of galactic objects was understood? Credit: A.C. Fabian.

In the cases Fabian is most interested in, people looking for one thing ran into quite another. He runs through other cases of unexpected discovery, making the reader wonder how many significant things are waiting to be found in data already on our hard disks and even locked up in old astronomical images. Who knows what mysteries might still unfold from a decades old Palomar photograph?

Fabian wonders whether there is a way to turn serendipity into a tool that can facilitate further discovery:

Does it not then make sense to tailor our research funding, both for the hardware – the telescopes – and for the modes of working, to take [serendipity] into account? This leads to a current dilemma. Facilities (and people) are increasingly expensive. Funding agencies using public funds want value for money so are most likely to fund projects and telescopes and teams where a successful outcome is predicted. This tends to mean looking into areas close to where we know, rather than stepping out into the unknown. In the case of serendipitous discovery there is little that can be predicted with certainty, we can only argue on the basis of past success. It means stepping out boldly in discovery space.

He goes on to argue in this paper that direct approaches to fundamental problems may sometimes make us too narrow in our investigation. Recalling that a good view of many celestial objects comes with averted vision rather than direct focus, he champions ‘general astronomical observatories of all wavebands’ as the best way to target the unexpected, adding:

It is ironic that our telescopes are remembered mostly for the serendipitous discoveries they made… and not for the issues for which the original science case was made, yet we put most of our efforts into the known science aspects of the science case for a new telescope. Rather like the common view of democracy, or peer review, this common approach is highly flawed but is however the best available.

I take this to mean that there may be no way to channel serendipity, but we should not forget the role it has played in past discovery. Fabian can cite examples from the Keck telescopes ranging from studies of Type I supernovae and the accelerating universe to the discovery of Pluto-sized dwarf planets. The paper is an intriguing survey of the chance element in discovery and one that emphasizes the importance of both preparation and openness to the unknown.

The paper is Fabian, “Serendipity in Astronomy,” to be published in Serendipity and available online.

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Galactic Dark Matter Modeled

I don’t spend too much time worrying about the ultimate fate of the Earth as it interacts with a swollen red Sun some five billion years from now. My thought is that if any civilization is still on the planet in a billion years, it will have long since worked out how to exit when necessary (and it will be necessary a lot sooner than five billion years!), or maybe how to tweak planetary orbits to preserve our planet, if only as a choice historical site.

Still less do I worry about the Milky Way being destroyed by a collision with one or more satellite galaxies, like the Large and Small Magellanic Clouds that move around the parent galaxy. So when I read that an Ohio State team led by Stelios Kazantzidis had shown via computer simulations that such a collision would leave the galaxy more or less intact, my real interest was in the implications of this work in terms of one of science’s great mysteries — the nature of dark matter. Have a look at the team’s modeling of the dark matter structure thought to surround galaxies like ours.

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Image: This image from a supercomputer simulation shows the density of dark matter in our Milky Way galaxy which is known to contain an ancient thin disk of stars. Brightness (blue-to-violet-to-red-to-yellow) corresponds to increasing concentration of dark matter. The bright central region corresponds roughly to the Milky Way’s luminous matter of gas and stars and the bright clumps indicate dark-matter satellites orbiting our Milky Way galaxy which are known as “substructure”. The simulation predicts that the dark-matter halos of spiral galaxies are lumpy, filled with hundreds of dark matter substructures that pass through the stellar disks of galaxies, leaving their imprint and disturbing them in the process. Credit: Stelios Kazantzidis, Ohio State University.

If galaxies are embedded within huge haloes of dark matter (the Milky Way’s halo is thought to be a million light years across, or ten times larger than the 100,000 light year width of the galaxy), then a filamentary model of dark matter running throughout the universe emerges, with the larger galaxies at the intersection of dark matter filaments. As this Ohio State news release suggests, satellite galaxies like the Magellanics would move along the strands of this web, gradually drawn into orbit around the larger galaxies.

Kazantzidis’ team ran computer simulations of galaxy formation to study this model, setting up collisions between satellite galaxies (and their associated dark matter) and the larger spiral galaxy. During the collision, the dark matter interacts gravitationally with the spiral galaxy. The result: The satellites pass through the galactic disk again and again, losing mass each time. The effect of their gradual dissolution is that the primary galaxy shows a distinctive signature that is consistent with observation.

Says Kazantzidis:

“We can’t know for sure what’s going to happen to the Milky Way, but we can say that our findings apply to a broad class of galaxies similar to our own. Our simulations showed that the satellite galaxy impacts don’t destroy spiral galaxies — they actually drive their evolution, by producing this flared shape and creating stellar rings — spectacular rings of stars that we’ve seen in many spiral galaxies in the universe.”

The next figure shows the formation of this unique flared shape:

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Image: Density maps of disk stars illustrating the global morphological transformation of a galactic disk subject to bombardment by dark matter substructures. Brighter colors indicate regions of higher density of disk stars. The left panel shows the initial disk, while the right panel depicts the final disk after the violent gravitational encounters with the orbiting substructures. The edge-on (upper panels) and face-on (bottom panels) views of the disk are displayed in each frame. Satellite-disk interactions of the kind expected in the currently favored cosmological model produce several distinctive signatures in galactic disks including: long-lived, low-density, ring-like features in the outskirts; conspicuous flares; bars; and faint filamentary structures above the disk plane that resemble tidal streams. These morphological features are similar to those being discovered in the Milky Way, the Andromeda galaxy, and in other spiral galaxies. Credit: Stelios Kazantzidis, Ohio State University.

So we have what Kazantzidis calls ‘a wealth of signatures’ that are both consistent with the current cosmological model (including dark matter) and consistent with observations of other galaxies. The flared edges of the above image, in which a disk that is narrow at the center widens toward the edges, are such a signature. The latest report on this work is in Kazantzidis et al., “Cold Dark Matter Substructure and Galactic Disks. II. Dynamical Effects of Hierarchical Satellite Accretion,” Astrophysical Journal 700 (2009), pp. 1896-1920 (abstract). A preprint is also available.

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