Top Ten Observatories

This is a list of the 10 greatest modern astronomical observatories ever imagined. Some are being built presently, some are scouring for funding, and some are dreams. They are in no precise order, but I have tried to place them according to their extremeness with respect to scientific impact, cost, technology, and size.

1. Laser Interferometer Space Antenna

LISA is in a class of its own.  In some sense it does not belong on this list because it literally transcends every other observatory on this list by monitoring the universe through gravitational waves and not electromagnetic waves.  If LISA is successful it will be the first direct observation (unless a project like advanced LIGO beats it to the punch) of gravitational waves which are predicted by Einstein's theory of General Relativity. LISA will detect the variation in distance of three spacecraft flying in an equilateral triangle formation. The LISA instruments are classic interferometers sensitive to gravitational  waves which distort the space-time between the spacecraft by as little as just tens of pm. Soon the LISA Pathfinder mission will be launched to prove the concept and technology necessary for the complete observatory. LISA is a profound step forward for humankind, like an infant opening its eyes for the first time.

2. Terrestrial Planet Finder

The TPF is visionary space mission which will likely consist of two observatories in space a coronagraph and an interferometer array.  The TPF will search for extrasolar terrestrial planets around relatively close stars like the Alpha Centauri system and systems where the probability to find an extra solar planet is high.  The coronagraph would be a very large optical telescope, at least three times that of Hubble, that would also have special optics to occult the light of bright stars in order to see the dim planets next to their brilliant host stars.  The interferometer, illustrated above, would consist of several small infrared telescopes orbiting in formation; the interferometric technique would allow the telescopes to obtain a resolution of a much larger telescope.

3. James Webb Space Telescope

The JWST is considered the successor to the Hubble Space Telescope.  It will study galaxy, star and planet formation in the Universe with supreme depth and precision.  Just imagine the James Webb Ultra Deep Field. The telescope engineering is impressive.  The telescope's primary mirror will consist of a 6.5 m (about 6 times the area of Hubble) gold coated beryllium refelector composed of 18 hexagonal segments which will unfold in space. The mirror is made of such special materials because of the need for specific thermal and reflective properties. For example beryllium is the metal with the greatest heat dissipation characteristics per unit weight and further its relatively low coefficient of thermal expansion imparts stability to the mirror.  JWST is designed to observe very distant objects such that much of their light will be in the infrared when it reaches the telescope and therefore JWST will be an infrared telescope, hence the gold coated reflecting surface.  JWST is packed with advanced technology like hemispherical resonator gyros which should last longer than the traditional mechanical gyroscopes which were on Hubble and needed servicing during missions. This is necessary because JWST will be far from earth at Lagrange point two, some 1.5 million km from Earth and not close enough for simple repair missions. If all this sounds ambitious and outlandish that is because it is, but the science that the JWST will produce will certainly justify the effort.

4. Overwhelmingly Large Telescope

The OWL is the most unlikely telescope on this list; the project has been eclipsed by the European Extremely Large Telescope, the EELT, on all practical accounts. The OWL would be a unrealistically large 100 m telescope allowing it to observe objects as faint as an apparent magnitude of 38.  In order to control costs the OWL would be based on mass production of major cost items like the structural components and segmented mirrors, but a review panel determined the cost would be at least 1.2 billion Euros. This cost is considered unacceptably high.

5. The Square Kilometer Array

The SKA will be a radio telescope with a million kilometers of collecting area. It will be the largest telescope ever created and perhaps the most expensive at 1.5 billion Euro. The SKA will probe the gaseous component of the early Universe with sensitivity 50 times greater than the Very Large Array. This sensitivity and a wide field of view will also allowing the SKA to probe general relativity by monitoring the timing of a network of pulsars. Like the VLA the SKA will be an interferometric array consisting individual antenna stations working together to synthesize an aperture with a diameter up to several thousand kilometers.  Many things about the final design for the SKA are uncertain, in fact factions within astronomy have threatened to doom the entire project. The disagreements stem from different opinions on what the primary scientific objectives should be for the project. Currently it is planned that approximately 50% of the collecting area would be contained in a dense central array of 5 km in diameter to provide high brightness sensitivity at arc-second scale resolution for studies of faint spectral lines from structures in the early universe. Another 25% of the collecting area would be located within a diameter of 150 km; the image above shows a possible layout for the array with arms in a spiral pattern with a diamter of 150 km. The remainng 25% of the collecting area would be at baselines of 3000 km or greater. The distribution of antennas directly impacts what kind of science can be accomplished. The video below shows a possible layout for the SKA in dramatic fashion.

6. European Extremely Large Telescope

The EELT is the realistic result of the OWL telescope proposal. The primary mirror will be 42 meters consisting of 984 1.4 meter segments of only 50 mm thickness.  The mirrors are thin in order to have excellent thermal properties. The EELT will have an adaptive optics system which will perform active adjustment of a 2.5 meter mirror to compensate for atmospheric affects which distort images. There will be 5000 actuators supporting this mirror which precisely adjust the mirror's shape thousands of times per second in order to correct images.  The reality is that the limiting effect on all large ground based telescopes is atmospheric seeing, therefore all the ground based optical telescopes on this list use some kind of adaptive optics.

7. Large Synoptic Survey Telescope

The LSST is an 8-meter telescope with a 3 degree field of view (consider that the moon is only half a degree in the sky).  This design configuration allows the LSST to implement an observing program that detects near-Earth objects which are small and faint in exposures of 10 or 20 seconds, and it allows images to be stacked for deep and wide imaging for star and galaxy surveys. The science mission drivers of LSST include the nature of dark energy, the solar system, optical transients, and galactic structure. It is the LSST technology and the rate at which it will produce data that makes it so remarkable. The LSST camera is 3200 Megapixels (it is a giant array of 189 CCD chips) and will create 400,000 sixteen Megapixel images per night (resulting in about 30 TB) for a total of 60 PB of raw data over 10 years. The total data volume after processing will be over 100 PB requiring 250 TFlops of computing power for processing. LSST will be wide, fast, and deep. It should be ready for first light by 2014.

8. Thirty Meter Telescope

The TMT is another extremely large ground based telescope. Its design calls for a collecting area that is thirty meters or about 100 feet in diameter. In order to better explore the early universe it will be sensitive to light in the optical near infrared. Relative to the Hubble the TMT will have 144 times more collecting area and a factor of 10 better spatial resolution in the near-infrared. The TMT will have a primary mirror composed of 492 segments with a rotating tertiary mirror (as seen in the above image, a Ritchey-Chretien telescope) in order to direct light onto multiple instruments and it will of course use adaptive optics to correct for turbulence in earth's atmosphere. The TMT will implement a scaled of version of the segmented mirror technology of the Keck telescopes at a size which will produce significant science at a reasonable cost.

9. Giant Magellan Telescope

The GMT differentiates itself from the other giant ground based telescopes on this list in that its primary mirror will not be segmented in the standard manner, but will instead consist of seven monolithic 8.4 m mirrors.  Because six of the mirrors are off-axis (they don't focus light to a point directly above them, but rather to a point off to their side; see image above) they present a unique engineering challenge that will synthesize a telescope with a resolving power of a single 24.5 m mirror.  Currently the first mirror has been cast at the Steward Observatory Mirror Lab as a proof of concept that an acceptably accurate shape can be achieved.

10. Atacma Large Submillimeter Array

ALMA is probably the most practical observatory on this list and it is almost already completed (located in the Atacama desert), whereas many of the other observatories on this list are only the twinkle in astronomer's eyes. It is currently under construction in the thin (altitude of 5,000 m or 16,000 feet), dry air, of northern Chile. ALMA is not actually a single telescope, but an array of 50 (this number may change and has already been reduced once) antennae working in unison. It merits a place on this list because it will revolutionize astronomy by providing a senstive eye on mm wavelength light where early universe star/planet formation can be viewed best. Each of its 12 m antennas will observe in bands ranging fom 30 Ghz to 1 Thz and the array will have specialized telescope transporters which will enable baselines ranging from 150 m to 16 km. ALMA is only practical in respect to the grandiose telescopes on this list; it the the most ambitious ground-based telescope ever built and costs in excess of one billion US dollars.

The future of great astronomical observatories

This list is merely my musings on astronomical observatories. There are more productive observatories that have already built, or will be built, but these are the most exciting in my humble opinion. This list does not include even more speculative projects such as plans for a lunar radio telescope or an extremely sensitive and larger LISA. There are other planned observatories not mentioned, like IXO, that just didn't make the list.

It is of note that there is an over arching principle of segmentation present in all of these observatories; these telescopes use multiple almost identical components working in unison in order to gather signal. LISA, the SKA, TPF, and ALMA use interferometry or correlation to observe. The EELT, TMT, JWST, use segmented primary mirrors. GMT uses several identical mirrors to simulate one primary mirror. LSST uses a massive array of CCD detectors. Modern technology and the economic/complexity benefits of reproducible industrial construction make this possible, but it takes modern computing to gather the data from the individual receiving elements and produce coherent observations and science.

To Hold The Sky

Galaxy Zoo 2

Galaxy Zoo is the worlds largest astronomy collaboration with over a hundred thousand collaborators. I mentioned Galaxy Zoo some time ago, but since then they have doubled the number of papers published from their collaboration and launched Galaxy Zoo 2. I want to discuss the impetus, implementation, and some of the results of the project here. It begins with the desire of astronomers to classify galaxies. And why would you want to classify galaxies? Well in order to learn about the cosmos, that is to learn about the properties of merging galaxies in the local universe, to learn about galaxy star formation, or to learn about the intrinsic spin of galaxies in our universe you may need to classify galaxies. The Galaxy Zoo collaboration has implemented the citizen science or crowd sourcing model in order to classify the million or so images of galaxies taken by robotic telescopes (like the Sloan Digital Sky Survey, SDSS, which produces images just like those seen here). Many years ago astronomers only had to inspect astronomical images by eye from photographic plates. The digital revolution has brought computers to bear on the problem as astronomers have implemented machine learning techniques such as neural networks in order to identify spiral from elliptical galaxies, but approaches like nueral networks are still limited by their training set size and are prone to errors. So as robotic survey telescopes have allowed us to gather a fantastic amounts of data technology has not been so successful at making sense of that data.

There have been several successful models for citizen science at home such Seti at Home and Folding at Home, but the most powerful computational device most people have at home is their own mind. The wisdom of crowds had already come to bear on one astronomical project, Stardust at Home, so galaxy classification was a natural application for citizen science. The Galaxy Zoo team had a simple approach to galaxy classification they implemented in Galaxy Zoo 1. They offer the user a single image, like those seen above, of a galaxy and 6 buttons:

The buttons are as follows: 1) Elliptical galaxy, 2) Clockwise spiral, 3) Anti-clockwise spiral,  4) Spiral Galaxy Other e.g. Edge on, Unsure, 5) Star or Don't Know, 6) Merger.  The system receives back a classification, but they show the same galaxy to many users such that they get multiple classifications for a single galaxy. The result of the multiple classifications for each galaxy is is statistical certainty. Even trained astronomers make mistakes and disagree on the classification of some galaxies therefore having many amateurs classify a galaxy is better than a few professional astronomers. The system they have developed is also quite sensitive to user idiosyncrasy with respect to the fact that they monitor user performance for individual tasks such as ability to identify galaxy bulges or spiral arms and then weight that user's responses according to their accuracy and consistency for each task. The great thing about having people's eyes on the data is that unexpected and unique discoveries are made possible. Computers make errors not discoveries.  The fantastic support for the project is very encouraging. They did a survey of over 10,000 users to discover their motivation. The most important motivator across all age groups was:

I want to contribute to science

The Cosmos isn't strange people are strange

All those good willed people, what could possibly go wrong? The Galaxy Zoo published a paper on the Chiral correlation function of galaxy spins, that is they investigate if spiral galaxies have a tendency to spin clockwise or counterclockwise, and they discovered more about people than galaxies. If galaxies had a spin tendency it would quite simply undermine physics because chirality is a fundamental property of particles and cosmology. Indeed they found a tendency for galaxies to spin counterclockwise, but when they began to display the mirrored images of the galaxies (expecting to receive more clockwise responses this time) they found the users behavior to be inconsistent.  This indicates that either people are strange or the user interface of Galaxy Zoo is strange. They sum up the results in their abstract:

After establishing and correcting for a certain level of bias in our handedness results we find the winding sense of the galaxies to be consistent with statistical isotropy. In particular we find no significant dipole signal, and thus no evidence for overall preferred handedness of the Universe.

This may seem like an obvious result because it is intuitively correct, but it is important to verify observationally what seems intuitively correct and further previous studies had found evidence for non statistical isotropy.

Hanny's Voorwerp

The unique discovery of Hanny's Voorwerp was made possible only by the citizen scientists of the project. Hanny's Voorwerp is a green amoeba like blob next to a spiral galaxy that was discovered by a galaxy zoo volunteer, Hanny van Arkel, and hence the name of the object.  It appears green in some optical images because of bright emission lines that dominate in the SDDS g band. Spectral analyis has shown that it is a highly ionized region leading to the hypothesis that it is the result of a powerful transient outburst because whatever energized the blob is now gone. Researchers hypothesize that Hanny's Voorwerp is a quasar light echo:

Hanny’s Voorwerp, is bright in the SDSS g band due to unusually strong [OIII] 4959, 5007 emission lines. We present the results of the first targeted observations of the object in the optical, UV and X-ray, which show that the object contains highly ionized gas. Although the line ratios are similar to extended emission-line regions near luminous AGN, the source of this ionization is not apparent. The emission-line properties, and lack of x-ray emission from IC 2497, suggest either a highly obscured AGN with a novel geometry arranged to allow photoionization of the object but not the galaxy’s own circumnuclear gas, or, as we argue, the first detection of a quasar light echo. In this case, either the luminosity of the central source has decreased dramatically or else the obscuration in the system has increased within 10⁵ years. This object may thus represent the first direct probe of quasar history on these timescales.

Galaxy Zoo 2: Mergers

The result of users classifying galaxies as mergers were 3000 prime candidates with which they wanted to compare to simulations. The goal of Galaxy Zoo 2 is to understand cosmic mergers. They use the crowd source model again because this allows exploring the entire parameter space quickly whereas a machine may often find a local solution, but would be limited in knowledge of  unique solutions. Galaxy Zoo 2 presents you, the user, with a 3x3 grid of galaxies. At the center is a real image of a galaxy and surrounding it are 8 simulated galaxies. You must select which simulations match the real image best. If you don't like any of your options you can click a button at the top and you get a slot machine effect of 8 new galaxies.  It is very satisfying to demand random sets of galaxies and wait for a winner that matches what you are looking for. I found myself looking at upwards of 500 galaxies for each galaxy merger I classified which sounds absurd until you try it and see how easy it is. After selecting a few galaxies you can fine tune your selected simulations within parameter space and then select your final best simulation. The entire application runs the simluations locally on the user's machine in Java so the Zoo leverages everything a user has to offer from their computer's CPU to their brain.

Science Zoo

There are more Zoos in development. Moon Zoo is coming soon which will be like Galaxy Zoo for classifying features on the lunar surface using high resolution images from the Lunar Reconnaissance Orbiter Camera. Other fields will also be using the Zoo model, but surely astronomy offers the most exciting and beautiful possibilities. Astronomy is facing a flood of data soon with next generation projects like the Large Synoptic Telescope coming online in a few years. LSST will produce some 30 terabytes of data a night. This may be such a large amount of data that volunteers wont be able to sift through it all. In this case volunteers could provide the training sets for machine learning systems that could accurately classify data. The Zoo model will continue because people want to contribute to science.


References:

Anze Slosar, Kate Land, Steven Bamford, Chris Lintott, Dan Andreescu, Phil Murray, Robert Nichol, M. Jordan Raddick, Kevin Schawinski, Alex Szalay, Daniel Thomas, & Jan Vandenberg (2008). Galaxy Zoo: Chiral correlation function of galaxy spins MNRAS, 392 (1225) arXiv: 0809.0717v2

Chris Lintott, Kevin Schawinski, William Keel, Hanny van Arkel, Nicola Bennert, Edward Edmondson, Daniel Thomas, Daniel Smith, Peter Herbert, Matt Jarvis, Shanil Virani, Dan Andreescu, Steven Bamford, Kate Land, Phil Murray, Robert Nichol, Jordan Raddick, Anze Slosar, Alex Szalay, & Jan Vandenberg (2009). Galaxy Zoo : 'Hanny's Voorwerp', a quasar light echo? MNRAS arXiv: 0906.5304v1