Globular Clusters and Astroengineering

Sahu, Anderson and King have determined that the increases in stellar brightness found by the HST WFPC2 were caused by cosmic ray hits [Sah02]  See also [Baa01, Hur00, Gau02, dlFM01]

Globular clusters are the among the densest star aggregations known to astronomers.  Because of this they are attractive targets to search for "planets" using the technique of gravitational microlensing.  This technique can detect dark objects, such as planets, passing through the line of sight between an observer and a more distant star because the gravity of the object causes the star to brighten for a brief period [Rhi96, Ben00].  In theory, it is unlikely that globular clusters should contain planets.  This is because the ultraviolet radiation from early massive stars should evaporate protoplanetary disks of less massive stars, significantly reducing the abundance of planets [Joh98, Arm00].  This idea was supported by Hubble Space Telescope studies of the globular cluster 47 Tucanae which found it to contain no planets [STSCI00, AIS00, Gil00, Bri00, Bro00].  However, more recent studies of the globular cluster M22 suggest that it does appear to contain many large dark objects [STSCI01, JPL01, Sah00, Sah01].  The frequency of such observations in M22 suggests that they may contain up to 10% of the cluster's mass.  Unfortunately these observations would seem to be in conflict with the premise that such objects are "planets" (in our solar system only 0.04% of the mass is found in the planets).

Can astroengeering by advanced technological civilizations  (ATC) solve the Astronomers' dilemma?  Perhaps.  Because of the high mass-to-volume and energy-to-volume densities in globular clusters these locations could be attractive locations for ATC to construct Matrioshka Brains [Bra97], Jupiter Brains [San99] or the large reversible computer architectures that can trump any non-reversible architecture [Fra98].  ATC may never communicate across the large volumes of empty space throughout most galaxies because the communication costs are very high relative to the quantity of information that may be exchanged.  Globular clusters provide interesting destinations for socially oriented ATC who are motivated to construct of multi-stellar Beowulf Clusters capable of performing what may be the largest useful computations feasible at this stage of the evolution of the universe.  Why might M22 exhibit these properties but not 47 Tucanae?  The simplest answer may be the fact M22 is located a mere 4.9 kpc from the center of the Milky Way (3.2 kpc from the sun) while 47 Tucanae is located 7.4 kpc from the galactic center (4.5 kpc from the sun) [Mil00, Har99, NGC95].  The travel time from locations where ATC may develop (in the Galactic Belt of Life [Mar86, Bal00, Gon01]), to M22 is likely to be much less than the travel time to 47 Tucanae.  This hypothesis might be tested by determining whether globular clusters nearer to the galactic center such as UKS 1 (0.8 kpc), NGC6558 (1.0 kpc) or NGC 6624 (1.2 kpc) appear to have greater abundances of dark objects.  A more complex analysis would determine the full orbits of the globular clusters around the galaxy for the last several billion years and compute which of those have had "close encounters" with the "Belt of Life".  Such close encounters enable the relatively inexpensive seeding of those globular clusters with ATC probes, or even the relocation of entire solar systems from a galactic orbits to globular cluster orbits.  The long term evolution of galaxies may exhibit interesting "selection effects" whereby ATC migrate to those globular clusters that exhibit indications of previous development by ATC that also orbit close to their galactic position at some point.  Globular clusters that exhibit no "colonization" by ATC and/or only orbit at locations that would be expensive to colonize could well be "undesirables" at this period of galactic development.

So, are the "dark objects" discovered in the various gravitational microlensing experiments "natural" or can the missing baryonic Dark Matter be accounted for by ATC astroengineering?  For now it seems to be an undecidable question.  All we can say for sure is that if projects like GEST [Ben00] get funded and launched, we may have a much larger collection of objects to consider.  Until advanced telescopes like SIRTF (est. launch: July 2002) or NGST (est. launch: 2009) are available and those observations coordinated with the microlensing observations all we can do is speculate.

References

1. Astronomy Information Service: "Planets rarer than we thought – Hubble search turns up blank" (3 November 2000).
2. Armitage, P., "Suppression of giant planet formation in stellar clusters", (July 2000); astro-ph/0007044.
3. Balázs, B., "SETI and the Galactic Belt of Intelligent Life", in the proceedings of "Bioastronomy 99: A New Era in Bioastronomy", 6th Bioastronomy Meeting, held at Kohala Coast Hawaii, August 2-6, 1999.
4. Baard, E., "Dark Worlds 'Discovery' Retracted", Wired News (19 Dec 2001).
5. Bennett, D. P., Rhie, S. H., "The Galactic Exoplanet Survey Telescope: A Proposed Space Based Microlensing Survey for Terrestrial Extra-Solar Planets" (January 2000); astrop-ph/0003102; See also GEST Home Page
6. Bradbury, R. J., "Matrioshka Brains" (1997).
7. Britt, R. R., "Distant Planet Hunt Strikes Out, But That's a Good Thing", Space.com (31 October 2000).
8. Brown, T., et al., "HST Photometry of 47 Tucanae: Time Series Analysis and Search for Giant Planets", AAS 196th Meeting, (Session 2: Searching for and Characterizing Extra Solar Planets) Bulletin of the American Astronomical Society 32(2):469 (June 2000); [Full Poster].
9. de la Fuente Marcos, R., de la Fuente Marcos, C, "Microlensing planets in M22: free-floating or bound?", Astronomy & Astrophysics submitted (2001).
10. Frank, M. P., Knight, T., Margolus, N., "Reversibility in optimal scalable computer architectures", in the proceedings of Unconventional Models of Computing '98 (Jan. 5, 1998)  Published as part of DMTCS Series: Unconventional Models of Computing C. S. Calude, J. Casti, M. J. Dinneen (eds.), Springer-Verlag, Singapore (1998).
11. Gaudi, B. S., "Interpreting the M22 Spike Events", Astrophysical Journal 566:???-??? (10 Feb 2002).
12. Gilliland, R. L. et al., "A Lack of Planets in 47 Tucanae from an HST Search", Astrophysical Journal Letters, in press; astro-ph/0009397 (25 Sep 2000).
13. Gonzalez, G., Brownlee, D., Ward, P., "The Galactic Habitable Zone I. Galactic Chemical Evolution", to be published in Icarus; astro-ph/0103165 (21 Mar 2001).
14. Harris, W. E., "Catalog of Parameters for Milky Way Globular Clusters", (22 June 1999); See also: Harris, W. E. , Astronomical Journal 112:1487 (October 1996).
15. Hurley, J. R., Shara, M. M., "Free-Floating Planets: Not So Surprising", Astrophysical Journal In Press (2000).
16. Johnstone, D., Hollenbach, D., & Bally, J., "Photoevaporation of Disks and Clumps By Nearby Massive Stars: Application to Disk Destruction in the Orion Nebula", Astrophysical Journal 499:758 (1998). [Abstract]
17. JPL Press Release: "Hints of Planet-sized Objects Bewilder Hubble Scientists" NASA JPL (27 June 2001).
18. L. Marochnik, L. M. Mukhin, "The Galaxy's Belt of Life", pp 41-46 in the Problem of the Search for Life in the Universe, Proceedings of the conference on SETI in Tallin, Estonia, USSR (December 7-11 1981), V. A. Ambartsumyan, N. S. Kardashev, V. S. Troitskii (eds), Nauka, Moscow (1986).
19. Milan, W., "Distribution of Milky Way Globular Clusters -- A Graphical Investigation" (2000).
20. The NGC/IC Project: NGC/IC Database:
1. Skiff, B. A., "Observational Data for Galactic Globular Clusters", Webb Society Quarterly Journal 99 (January 1995, 2 May 1999).
2. Skiff, B. A., "Precise Positions for the NGC/IC Planetary Nebulae", Webb Society Quarterly Journal 105:15 (July 1996).
21. Rhie, S. H., "Microlensing Planet Search Project" (1996).
22. Sandberg, Anders, "The Physics of Information Processing Superobjects: Daily Life Among the Jupiter Brains",  Journal of Transhumanism 5 (1999).
23. Sahu, K., Casertano, S., Livio, M., Potter, M., "Detection of low-mass objects in M22 through Microlensing", AAS 196th Meeting, (Session 2: Searching for and Characterizing Extra Solar Planets) Bulletin of the American Astronomical Society 32(2):488 (June 2000).
24. Sahu, K. C., Casertano, S., Livio, M., Gilliland, R. L., Panagia, N., Albrow, M. D., Potter, M., "Gravitational microlensing by low-mass objects in the globular cluster M22". Nature 411:1022-1024 (28 June 2001).
25. Sahu, K. C., Anderson, J., King, I. R., "A Re-examination of the "Planetary" Lensing Events in M22". Astrophysical Journal Letters [accepted] (2002).
26. STSCI Press Release #STScI-PR00-33: "Astronomers Ponder Lack of Planets in Globular Cluster" (31 October 2000).
27. STSCI Press Release #STScI-PR01-20: "Hint of Planet-Sized Drifters Bewilders Hubble Scientists" (27 June 2001).

Related (sometimes loosely) Sources

1. Broderick, D., "The Spike: How Our Lives are Being Transformed by Rapidly Changing Technologies", Forge, New York (2001).  Matrioshka Brains and Globular Clusters are discussed on pgs 304-308.
2. Rhoads, J. E., Malhotra, S., "Microlensing of Globular Cluster Stars as a Tool for Galactic Structure Studies", AAS 191st Meeting, (Session 83: Gravitational Lensing) Bulletin of the American Astronomical Society 29(5):488 (January 1998).
3. w151: Low Mass Stars in Globular Clusters
4. ESO Southern Observatory: "Unexpected Anomalies in Globular Clusters Found" (13 Mar 2001).
5. Astrodot.org