Science Mission Overview
Cosmic Discovery in the 21st Century
The defining event in modern astronomy, and perhaps all of 20th century science, was the discovery of the Universe beyond the Milky Way. The determination of the vast extent and dynamic expansion of the Universe by Hubble and other astronomers set the stage for modern Cosmology and humankind’s understanding of our place in the cosmos. We look forward to a new century of profound discovery led by generations of astronomers working at the forefront of Cosmology, Cosmogony and Astrophysics. The Giant Magellan Telescope can open a path to fundamental discoveries about the birth of stars and planetary systems, the mysteries of black holes and the genesis of galaxies.
The Birth of Stars and Planets
The Universe is populated with countless galaxies, and within them stars like our Sun are the basic source of energy and light. The 20th century was witness to enormous progress in our understanding of how stars evolve and produce the heavy elements necessary for life. In the last thirty years we have begun to understand how stars and their planetary systems form. Dozens of planets have recently been detected in orbit around other stars. We are driven to know whether solar systems like our own are common among the billions of stellar systems that comprise our Milky Way galaxy or if we are truly alone in the Cosmos.
The discovery of extrasolar planetary systems very unlike our own upset many preconceptions and left numerous unanswered questions regarding their formation. How, where, and when are planets born in the disks that encircle young stars? How common are gas giant (i.e. Jupiter-like) planets? Are giant planets helpful or harmful to the emergence of life-sustaining worlds? Are Earth-like terrestrial planets rare or common and how do they obtain the materials necessary for life?
These questions are best addressed by a telescope with the power to detect light from very faint objects, the ability to distinguish fine detail despite the blurring effect of the Earth's atmosphere and sensitivity to infrared heat radiation from forming stars and planets. The GMT, with its large collecting area and exquisite image quality, meets the demanding requirements of extrasolar planetary studies.
Presently we are able to detect planets only by indirect means. The GMT will allow us to make images of planets around nearby stars and, possibly, discern their chemical compositions. Designed with high contrast imaging in mind, the GMT will have the ability to detect faint terrestrial-like planets in the presence of enormous glares from their parent stars.
Despite the fact that stars are fundamental galactic building blocks, we do not yet have a deep understanding of how they form. Key issues include understanding the distribution of stellar masses, the number of failed “brown dwarf” stars, and the role of magnetized outflows in the formation of stars and planetary disks. The southern hemisphere location of the GMT provides access to the nearest and richest regions of star formation in the Milky Way. Joint investigations with the international Atacama Large Millimeter Array - the next generation probe of cosmochemistry – will allow powerful studies of the dense clouds of molecular gas and dust that harbor forming stars and their planetary systems.
The Formation and Evolution of Black Holes
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One of the most intriguing predictions of Einstein’s General Relativity is the existence of singularities, better known as Black Holes. Astronomy has provided spectacular confirmation of the existence of Black Holes, from solar-mass scales to the super massive Black Holes – singularities containing the mass of billions of stars. Recent evidence has shown that massive black holes are commonplace in the Universe and that intermediate-mass Black-Holes may be wandering throughout much of intergalactic space. Our own Milky Way contains a central Black Hole with a mass one million times that of the Sun. There appears to be a close connection between galaxy formation and Black Hole formation, but the mechanisms that link the two are not understood. The typical galaxy harbors a Black Hole containing 0.5% of the galaxy’s central stellar mass. Why the mass of stars and that of the central singularity should be in a constant ratio is a great mystery. Did the earliest stars and Black Holes form at the same time, or did the Black Hole dictate the efficiency of star formation in young galaxies? Why are some Black Holes (like the one in the Milky Way) dark, while others host Quasars, the most luminous objects in the Universe? The solutions to these puzzles lie, in part, in observations of black holes in distant, and hence young, galaxies. The GMT, operating with adaptive optics to achieve its maximum resolving power, can probe the centers of distant galaxies in unprecedented detail.
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The Birth of Galaxies and Cosmic Structure
Roughly 100,000 years after the Big Bang the Universe cooled to a neutral gas of Hydrogen and Helium of nearly perfect smoothness. Tiny seeds of higher than average density grew to eventually form the stars and galaxies that we see today. The physical processes, and even the time-line, of the birth of galaxies and structure from the smooth primordial gas remains largely the domain of theory, rather than observation. Recent gains in observations of distant galaxies and the Cosmic Background Radiation suggest that detection of the “first light” may not be far away. Many critical unknowns remain: were the first objects to form stars or black holes? Did galaxies form from the gradual agglomeration of many smaller units, or did some of them form in spectacular bursts of star formation? Were the first galaxies swathed in dust and thus hidden from direct observation except at long wavelengths? We now believe that the first luminous objects formed less than 1 billion years after the Big Bang. The light from these first stars will be redshifted into the near-IR region of the spectrum, between 1 and 2.5 microns - where the GMT will have its best performance.
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The existence of Dark Matter, non-luminous material whose presence is felt only through its gravitational pull, was first deduced from the dynamics of galaxy clusters. Detailed dynamical studies of spiral galaxies revealed that Dark Matter is the dominant form of mass in most, and perhaps all, galaxies. We now believe that 80% of the mass of the Universe is in this invisible form. Very little is known about this mysterious matter. Essentially all of our knowledge regarding its properties comes from astronomical observations. The GMT will have the ability to probe the signatures of Dark Matter, primarily through its gravitational bending of light, on finer scales than possible before.
Even more exotic than Dark Matter is the recently discovered Dark Energy. In a Universe containing only matter, the cosmic expansion is retarded by the mutual gravitational attraction of galaxies. Whether the Universe expands forever or eventually re-collapses depends on the density of gravitating matter. The remarkable discovery in recent years that the cosmic expansion is accelerating rather than slowing has revolutionized our understanding of the Universe. The Dark Energy that drives this acceleration may be related to Einstein’s Cosmological Constant, or it may be the manifestation of a form of exotic energy not predicted by current theories. At present our only direct measurements of the expansion history of the Universe come from observations of distant Supernovae – exploding stars, some of which leave behind Black Holes.
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Current ground-based telescopes cannot probe supernovae to sufficient distances to provide a definitive test of competing models of the Dark Energy. The GMT will allow us to observe Supernovae to the highest redshifts and will aid in the full characterization of the expansion history of the Universe.
An Innovative New Technology Telescope built on a Heritage of Success
One might ask why we should embark on a new telescope project now that the Magellan telescopes are in operation. The science questions outlined above highlight the need for significant gains in sensitivity and resolution. Technology has driven many of the ground-breaking discoveries in Astronomy and this motivates our desire to create the most powerful scientific instruments possible. George Ellery Hale set the standard in this respect when he quickly progressed from the Mt. Wilson 60inch and 100inch telescopes to the then-limiting aperture of the 200inch Hale telescope at Palomar Mountain. The Hale telescope defined the limit of telescope making for a half century. Astronomers worldwide are once again probing the new limits to telescope aperture. With the completion of the 6.5m Baade and Clay telescopes the Magellan Partner Institutions have established themselves once more as world leaders in the development of large telescopes. The GMT is an innovative approach to moving past the size limit for casting and polishing individual glass elements. While the Magellan telescopes each have a single mirror that is 6.5 meters in diameter, the GMT will be built from 7 mirrors, each 8.4 meters in diameter. The collecting area of the GMT will be 12 times that of a Magellan telescope and its spatial resolving power will be 10 times that of the Hubble Space Telescope. The total gain in sensitivity compared to the 6.5m Magellan telescopes is more than a factor of 100 in the diffraction limited regime.
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One
of the limiting factors in the performance of ground-based telescopes
is the blurring introduced by the Earth’s atmosphere. The GMT will use
the latest in adaptive optics technology to correct for image
degradation due to atmospheric turbulence. A deformable mirror composed
of a thin glass shell and thousands of mechanical actuators will adjust
its shape 100 times each second to match the image distortions induced
by the atmosphere. This sharpening of the images allows the telescope
to work to its full potential, both in terms of sensitivity and angular
resolution. Our telescope design strikes a perfect balance between
innovation and proven technology. As such it represents a bold
initiative by the GMT partner institutions as they seek to maintain
their place at the forefront of cosmic discovery in the new millennium.
GMT Technical Facts
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