Image<\/strong>: Two Airy disks at various spacings: (top) twice the distance to the first minimum, (middle) exactly the distance to the first minimum (the Rayleigh criterion), and (bottom) half the distance. This image uses a nonlinear color scale (specifically, the fourth root) in order to better show the minima and maxima. <\/p>\nHere we have another useful term: An Airy disk is a diffraction pattern that is produced when light moves through the aperture of a telescope system. Light diffracts \u2013 it\u2019s in the nature of the physics \u2013 and the Airy disk is the best focused spot of light that a perfect lens with a circular aperture can make. We\u2019re looking at light interfering with itself, so in the image, we have a central bright spot with surrounding rings of light and dark. The diffraction pattern depends upon the wavelength being observed and the aperture itself. This diffraction can be described as a point spread function (PSF) for any optical system, and essentially governs how tightly that system can be focused.<\/p>\n
Bigger apertures matter as we try to deal with these limitations, and the Giant Magellan Telescope will doubtless make many discoveries, as will all of the coming generation of Extremely Large Telescopes. But when we want to see ever smaller objects at astronomical distances, we run into a practical problem. Nothing in the physics prevents us from building a ground-based telescope that could see an Earth-class planet at Alpha Centauri, but if we want details, Fleming notes, we would need a mirror 1.8 kilometers in diameter to retrieve a 40 X 40 pixel image. <\/p>\n
The point of Fleming\u2019s talk, however, was that we can use quantum technologies to nudge into the Rayleigh limitations and extract information about amplitude and phase from the light we do collect. That, in turn, would allow us to distinguish between point sources that are closer than what the limit would imply. The operative term is super-resolution, a topic that is growing in importance in the literature of optics, though to this point not so much in the astronomical community. This may be about to change.<\/p>\n
Counter-intuitively (at least insofar as my own intuitions run), a multi-aperture telescope does a better job with this than a large single-aperture. Instead of a 3-meter mirror you use three 1.7 meter mirrors that are spaced out over, perhaps, an acre. This hits at mirror economics as well, because the costs of these enormous mirrors goes up more than exponentially. The more you can break the monolithic mirror into an array of smaller mirrors, you can add to the data gain but also sharply reduce the expense.<\/p>\n
In terms of the science, Fleming noted that the point spread function spreads out when multiple smaller mirrors are used, and objects become detectable that would not be with a monolithic single mirror instrument. The technique in play is called Binary Spatial Mode Demultiplexing. Here the idea is to extract quantum modes of light in the imaging system and process them separately. The central mode \u2013 aligned with the point spread function of the central star \u2013 is the on-axis light. The off-axis photons, sorted into a separate detector, are from what surrounds the star.<\/p>\n
So in a way we\u2019re nudging inside the Rayleigh Limit by processing the light, nulling out or dimming the star\u2019s light while intensifying the signal of anything surrounding the star. I\u2019m reminded, of course, of all the work that has gone into coronagraphs and starshades in the attempt to darken the star while revealing the planets around it. In fact, some of the earliest research that convinced me to write my Centauri Dreams book<\/em> was the work of Webster Cash out at the University of Colorado on starshades for this purpose, with the goal of seeing continents and oceans on an exoplanet. I later learned as well of Sara Seager\u2019s immense contributions to the concept.<\/p>\nThus far the simulations that have been run at the University of Arizona by Fleming\u2019s colleagues have shown far higher detection rates for an exoplanet around a star using multi-aperture telescopes. In fact, there is a 100x increase in sensitivity for multi-aperture methods. This early work indicates it should be possible to identify the presence of an exoplanet in a given system with this ground-based detection method. <\/p>\n
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Can we go further? The prospect of direct imaging using off-axis photons is conceivable if futuristic. If we could create an image like this one, we would be able to study this hypothetical world over time, watching the change of seasons and mining data on the land masses and oceans as the world rotates. The possibility of doing this from Earth\u2019s surface is startling. No wonder super-resolution is a growing field of study, and one now being addressed within the astronomical community as well as elsewhere. <\/p>\n
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Exoplanet Detection: Nudging Into the Rayleigh Limit We\u2019re building some remarkably large telescopes these days. Witness the Giant Magellan Telescope…<\/p>\n","protected":false},"author":1,"featured_media":1648,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[],"class_list":["post-1647","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-space-testing-of-earth-life"],"_links":{"self":[{"href":"https:\/\/mycbh.com\/Games\/spaceperium\/wp-json\/wp\/v2\/posts\/1647","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mycbh.com\/Games\/spaceperium\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mycbh.com\/Games\/spaceperium\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mycbh.com\/Games\/spaceperium\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mycbh.com\/Games\/spaceperium\/wp-json\/wp\/v2\/comments?post=1647"}],"version-history":[{"count":0,"href":"https:\/\/mycbh.com\/Games\/spaceperium\/wp-json\/wp\/v2\/posts\/1647\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/mycbh.com\/Games\/spaceperium\/wp-json\/wp\/v2\/media\/1648"}],"wp:attachment":[{"href":"https:\/\/mycbh.com\/Games\/spaceperium\/wp-json\/wp\/v2\/media?parent=1647"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mycbh.com\/Games\/spaceperium\/wp-json\/wp\/v2\/categories?post=1647"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mycbh.com\/Games\/spaceperium\/wp-json\/wp\/v2\/tags?post=1647"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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