Brown Dwarfs in the Billions

Brown dwarfs are often called ‘failed stars,’ objects without enough mass to sustain the hydrogen-to-helium fusion reaction that powers the Sun. They’re dim enough that it was only in 1995 that the first brown dwarf, Gliese 229B, was discovered and the spectral classes L and T created to accomodate the category. The nearest known brown dwarfs are found around the star Epsilon Indi, a main sequence K-5 dwarf star; intriguingly, the first brown dwarf discovered in the system was subsequently found to have another brown dwarf orbiting it.

A brown dwarf

Image: An artist’s impression of a brown dwarf, a ‘failed star’ too cool to sustain nuclear fusion. Credit: Douglas Pierce-Price, Joint Astronomy Centre (Hilo, HI).

Now a team from Arizona State University led by Russell Ryan has used date from the Hubble Space Telescope to look for brown dwarfs above and below the galactic plane, with an eye toward determining their total population in the Milky Way. The team’s near infrared data tracked down 28 stars apparently fitting the L and T spectral types in a disk roughly 2200 light years thick. Their projections based on this survey conclude that 100 billion brown dwarfs populate the Galaxy, a number as large as that normally associated with normal stars.

For more, see Russell Ryan, Nimish Hathi, Seth Cohen et al., “Constraining the Distribution of L- & T- Dwarfs in the Galaxy,” now available at the arXiv site, and planned for a future issue of Astrophysical Journal Letters. Astronomer and author Ken Croswell offers a summary of the team’s work here. From Croswell: “Despite their impressive number, brown dwarfs add little weight to the Galaxy and do not account for its dark matter. Ryan’s team estimates brown dwarfs contribute roughly a billion solar masses to the Milky Way–only 0.1 percent of the Galaxy’s total. Altogether, the Galaxy has roughly a trillion solar masses, most of which is dark matter.”

Centauri Dreams‘ take: If brown dwarfs are as common as normal stars, we can expect to find others closer to us than Epsilon Indi. Indeed, our catalog even of M-class red dwarfs within 100 light years of the Sun is by no means complete, and it would surprise few astronomers to find a brown dwarf nearer than the Alpha Centauri system, currently considered the closest stars to Earth. The trick is tracking down these dim objects in the first place, but we can expect numerous new brown dwarf discoveries as the next generation of large Earth-based telescopes begins to come online.

On the Evolution of Science Fiction

Is science fiction a predictive medium, or is it, as I have opined before in Centauri Dreams, a diagnostic form of writing, telling us more about the times we live in than any purported future it describes? The question is occasioned by SF writer and scholar James Gunn, whose essay “Tales from Tomorrow,” available online and in the August/September issue of Science & Spirit, synopsizes the evolution of science fiction from Mary Wollstonecraft Shelley’s attempt to “…unfold to the world the deepest mysteries of creation” to recent work like Greg Egan’s Permutation City, where the mysteries of uploading human personalities into computers take center stage.

Author James GunnHere Gunn discusses the development of the genre in the early magazines, as edited by Hugo Gernsback and the legendary John Campbell:

While there were few science fiction books to speak of until 1946, what evolved through magazines like Gernsback’s was a literature of ideas and, more important, a literature of change and anticipation. As a Darwinian fiction that has at its heart a belief in the adaptability of the human species, science fiction itself naturally evolves—and, indeed, science fiction is at its best when it is most innovative. At least for a time, a belief in the power of rationality and the survival—even the dominance—of the human species underpinned most works of science fiction. (This philosophy was most apparent under the stewardship of John W. Campbell Jr., who became editor of Astounding Science Fiction magazine in 1937 and attracted writers like Robert A. Heinlein and Isaac Asimov, who shared his vision.)

Image (above): Science fiction author and critic James Gunn.

Today’s SF, Gunn believes, is less likely to focus on space exploration for its own sake; the genre has likewise moved away from the ‘alien goodwill’ period of the 1970s and ’80s (think Close Encounters of the Third Kind, or E.T.) and into the dark universe of novels like George Zebrowski’s The Killing Star, where life on the galactic level is a matter of destroying other civilizations because they will, acting on their own imperatives, try to destroy you.

Gunn moves through SF utopias and dystopias (emphasizing John Brunner’s extraordinary Stand on Zanzibar, a 1968 novel that uses techniques reminiscent of John Dos Passos) to works on economics and social organization, but he notes that all of these play into the genre’s focus on rapid technological change. “Science fiction,” he writes, “is inextricably linked to the rise of the machine’s role in society; indeed, the origins of science fiction can be traced to the Industrial Revolution and James Watts’ perfection of the steam engine. Science fiction writers have had a love-hate relationship with machinery ever since. As C.P. Snow noted in his famous “Two Cultures” lectures, literary authors feared the machine, while science fiction writers either embraced it or approached with caution.”

Given all that, it’s ironic how poorly science fiction anticipated the computer; most of the classic works growing out of computer networking come well after the technology had demonstrated its powers, even William Gibson’s Neuromancer (1984), which was written at a time when the capabilities demonstrated by the ARPANET had already begun to take hold in university networks. Few stories presage the emergence of computing power on the home desktop (a surprising exception: Murray Leinster’s 1946 story “A Logic Named Joe.”) The certainties of scientific progress have given way, in Gunn’s view, to a questioning about the role of science itself, a natural part of the evolution of a field that he believes is always marked by change.

1946 AstoundingGunn’s apparent belief that other genres — the detective story, the romance, the western — do not themselves evolve is perplexing. All it takes is one Ruth Rendell novel to demonstrate how lively and malleable the mystery genre remains, while thriller enthusiasts have only to check Martin Cruz Smith’s superb December 6 to see how genre conventions can be refreshed and reshaped. Perhaps Gunn’s essay is itself diagnostic, for it demonstrates a certain widely-held complacency of outlook among SF practitioners that some of us think restrains rather than elevates the field. If so, it’s a rare misstep for Gunn, who remains the greatest living scholar of science fiction and one of its most capable contributors.

Image: The March, 1946 issue of Astounding Science Fiction, containing Murray Leinster’s “A Logic Named Joe” (written under his pseudonym Will F. Jenkins). Astounding led the field in its day with an emphasis on rationality and a fascination with pushing scientific method to its limits to uncover new technologies.

Barnard’s Star: A Planetary Detection Gone Wrong

The Project Daedalus starship, designed by members of the British Interplanetary Society in the 1970s, was the first full-scale attempt to work out the parameters of a realistic interstellar mission. The target of this unmanned probe was Barnard’s Star, a red dwarf some 5.9 light years from Earth. The Daedalus team leader, Alan Bond, made a key assumption: technology had reached the point where an interstellar mission could be designed without assuming any further breakthroughs in physics.

The inertial confinement fusion techniques Daedalus would use have been the subject of much refinement in the days since and continue to be fertile ground for study. But the question I most often hear about Daedalus is, why Barnard’s Star, when the Alpha Centauri system is considerably closer? The answer is addressed in an article by astronomer Alan Boss (Carnegie Institution of Washington) that appears on the Astrobiology Magazine Web site. And it involves a planetary detection that only failed due to the limits of its instrumentation.

Project Daedalus Final ReportThe story goes back to astronomer Peter Van de Kamp, who in 1937 became director of Sproul Observatory at Swarthmore College. Van de Kamp began observing Barnard’s star the following year, taking 25 years worth of data in all before declaring there was evidence of a wobble in the star, one that would fit the profile of a planet about 1.6 times Jupiter mass orbiting at 4.4 AU. For about ten years, the idea that Barnard’s Star had at least one planet was in the air, influencing the Daedalus team and creating a ripple of interest that long preceded today’s active program of exoplanetary discovery.

Later work by Oliver Jensen and Tadeusz Ulrych went even further, suggesting the presence of three planetary companions of Jupiter size around the star (Astronomical Journal, Vol. 78, p. 1104, 1973). Unfortunately, followup studies by George Gatewood (University of Pittsburgh) and John Hershey (also at the Swarthmore College Observatory) found systematic errors in Van de Kamp’s work. Changes to the Swarthmore telescope, including a significant lens adjustment, were evidently the source. Hershey supplied the coup de grâce, using the Swarthmore instrument to find an identical wobble for the star Gliese 793, like Barnard’s Star an M-class dwarf.

Either both stars were orbited by an identical planet, or the telescope itself was the source of the erroneous data signature. Still unconvinced, Van de Kamp continued to study the star using completely new data, but without result. And much more recent work using the Hubble Space Telescope has revealed no convincing sign of planets.

For more on Daedalus, see A. R. Martin, ed., Project Daedalus Final Report. Supplement to the Journal of the British Interplanetary Society, 1978. We could use an updated new edition of this work to spare hapless researchers the task of making photocopies of several hundred pages of JBIS! Several papers in the Final Report consider the Barnard’s Star question. From Anthony Martin’s “Project Daedalus: the Evidence for Planetary Companions of Barnard’s Star:”

“However, since the above review [Jensen and Ulrych] was published, the situation has become less clear cut. Evidence for instrumental variations in the astrometric positions of a number of stars studied at the Sproul Observatory has been confirmed, although the amount of variation is appreciable for some stars and absent for others. Also, work by other astronomers…using more sophisticated approaches to reduction of observational data is not in very good agreement with the Sproul data.”

End of story, at least for now. What this suggests is that Barnard’s Star is probably not orbited by Jupiter-class planets within range of current detection methods, but it does not rule out smaller worlds that may only be found through more advanced instruments like the space-based Kepler.

7th Annual NIAC Meeting in October

Among papers to be presented at the upcoming NASA Institute for Advanced Concepts meeting are several that catch the eye from an interstellar perspective:

  • Alexey Pankine, Global Aerospace Corporation
    Sailing the Planets: Science from Directed Aerial Robot Explorers
  • Constantinos Mavroidis, Northeastern University
    Bio-Nano-Machines for Space Applications
  • John Slough, University of Washington
    The Plasma Magnet
  • These are among the papers to be presented by Phase II fellows of NIAC; i.e., those whose work has received a second round of NIAC funding. More lectures are to be announced before the meeting, which takes place October 10-11 in Broomfield, CO (30 minutes from the Denver airport). Those interested in attending should contact Katherine Reilly at with their name, affiliation, email address, telephone number and specific dates of attendance. There is no charge for registration.

    A number of poster presentations will also be available, including three
    intriguing antimatter discussions:

  • James Bickford, Draper Laboratory
    Extraction of Antiparticles Concentrated in Planetary Magnetic Fields
  • Gerald P. Jackson, Hbar Technologies, LLC
    Antimatter Harvesting in Space
  • Gerald A. Smith, Positronics Research LLC
    Positron-Propelled and Powered Space Transport Vehicle for Planetary Missions
  • Centauri Dreams discussed both Jackson and Bickford’s work in a previous post. More on the NIAC meeting as things develop. The meeting site is the Omni Interlocken, located at 500 Interlocken Blvd., Broomfield, Colorado 80021.

    A Stunning View of Interstellar Dust

    Centauri Dreams has discussed the problem of interstellar dust for fast-moving probes before. Here the issue is highlighted in a Gemini Observatory image of NGC 6559, part of the large star-forming region in the southern constellation Sagittarius. The dark structure — Gemini likens it to a Chinese dragon — is the result of cool dust that absorbs background radiation from the surrounding hydrogen gas. The region, some 5000 light years away toward the center of the Milky Way, is a reminder that in many areas, space is anything but empty.

    Image credit: Gemini Observatory (using the Gemini South telescope at Cerro Pachón in the Chilean Andes).