New Worlds, New Horizons in Astronomy and Astrophysics (2010) / Chapter Skim
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Pages 35-78
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From page 35... ...
Over the next decade we will be able to trace our origins, from the quantum fluctuations that seeded galaxies in the infant universe, to the origin of atoms and dark matter, to the first stars and galaxies, and to the formation of planetary systems like ours. We are also primed to understand how the most exotic objects in the universe work, including supermassive black holes and neutron stars, as well as to figure out how planetary systems form, how common are planets in the habitable zone around stars, and how to find evidence for life elsewhere.
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From page 36... ...
In the coming decade, an optimized and coordinated set of facilities on the ground and in space will test whether the simplest hypothesis -- dark energy is the quantum energy of 1 The charge to the SFPs and their findings are summarized in Appendix A Their reports are con tained in the present report's companion volume, National Research Council, Panel Reports -- New Worlds, New Horizons in Astronomy and Astrophysics, The National Academies Press, Washington, D.C., 2011.
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From page 37... ...
In the coming decade, powerful new observatories on the ground and in space will allow us to push back to still earlier times and glimpse the end of the cosmic dark ages signaled by the formation of the first-ever luminous sources in the universe -- the first generation of stars. Closer to home, the past decade has seen the discovery of well over 400 planets orbiting nearby stars.
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From page 38... ...
Lower: adaptive optics image obtained at the Gemini and Keck Observatories of three planetary-mass objects orbiting the nearby a star HR 8799. The bright light from the star has been subtracted to enable the faint objects to be seen.
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From page 39... ...
Like electromagnetic waves, gravitational waves span a spectrum, with more massive objects typically radiating at longer wavelengths. These ground-based experiments will probe the short-wavelength part of the spectrum, enabling us to observe the mergers of neutron stars and possibly to see the collapse of a stellar core in the fiery furnace of a supernova explosion.
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From page 40... ...
A French and European Space Agency precursor to Kepler, called COROT, has during its 2½ years of observations already detected planets as small as about 1.7 times the diameter of Earth. With these missions in operation, we will know in the next 5 years just how common Earth-size planets located on short orbits close to their stars might be in our galactic neighborhood.
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From page 41... ...
The Spitzer infrared space telescope has measured the light from a number of Jupiter-class exoplanets, hence determining atmospheric compositions. HD80606b, a giant planet observed by Spitzer, has an elliptical orbit that brings it alternately close to and far from its parent star so that its atmospheric temperatures change by many hun dreds of degrees Celsius over 6 hours.
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From page 42... ...
Powerful tests of our understanding of how black holes and galaxies form and evolve will be possible. We are on the verge of a new era of discovery in gravitational wave astronomy.
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From page 43... ...
Binary neutron stars and black holes merge, emitting, in addition to bursts of radiation, gravity waves. Supermassive black holes in the centers of galaxies swallow mass episodically and erupt in energetic outbursts.
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From page 44... ...
Many gamma-ray bursts are associated with the supernova explosions of massive stars. The powerful bursts of gamma rays are produced by hot gas moving outward through the collapsing star at close to the speed of light.
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From page 45... ...
The merging of two black holes, the growth of disks and the planets that form within them, the origin of large-scale structures that span the cosmos, and the formation of galaxies from the cosmic web are examples. Such simulations have great potential for discovery because they can illuminate the unanticipated behavior that can emerge from the interactions of matter and radiation based on the known physical laws.
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From page 46... ...
Rather, they also sprang from the imagination of inspired theorists thinking in deep and original ways about how to understand the data, and making testable predictions about new ideas. Examples range from the prediction that the chemical elements heavier than hydrogen and helium must have been created inside nuclear furnaces in the cores of stars, to the idea that the infant universe underwent a period of extremely rapid expansion called inflation, to the prediction of exotic objects like black holes, neutron stars, and white dwarfs, and the prediction that planets are a typical by product of normal star formation.
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From page 47... ...
SOURCe: NaSa/Wilkinson Microwave anisotropy Probe Science Team. Right: The same feature can be seen in the distribution of galaxies around us today as exhibited by the Sloan Digital Sky Survey in a 2.5-degree-thick slice of the north ern equatorial sky where color corresponds to galaxy luminosity.
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From page 48... ...
The CMB is therefore a fan tastic signal telling us about the early universe.4 The First Sources of Light and the End of the Cosmic Dark Ages Following the recombination and the formation of the first atoms, the early universe was a nearly formless primordial soup of dark matter and gas: there were no galaxies, stars, or planets. The background radiation had a temperature that quickly cooled to a temperature below that of the coolest stars and brown dwarfs known today.
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From page 49... ...
SOURCe: NaSa Wilkinson Microwave anisotropy Probe Science Team. This event signaled the end of the dark ages and the dawn of the universe as we know it today.
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From page 50... ...
new worlds, new HorIzons astronoMy astroPHysIcs 0 In and FIGURe 2.6 Top: Schematic of the evolution from left to right of an inflationary universe to recombina tion to reionization and first star/galaxy formation to today's earth-bound telescopes. Overlaid in tiles are predicted 21-cm signals from the Murchison Widefield array.
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From page 51... ...
. There is also growing evidence that many gamma-ray bursts are the explosive deaths of very massive stars and sometimes resulting in the formation of the first generation of black holes with the unusual chemical compositions expected for the first stars (nearly devoid of elements heavier than hydrogen and helium)
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From page 52... ...
Over the next decade it will be a high priority to extend such precision mapping over cosmic time: to have, in effect, a 13-billion-year-long movie that traces the buildup of structure since the universe first became transparent to light. This can be done by using radio telescopes to provide more detailed maps of the cosmic microwave background and to detect the atomic hydrogen gas all the way back into the dark ages; large spectroscopic surveys in the visible and near-infrared to trace the distribution of galaxies; gravitational lensing to trace the distribution of the dark matter halos; ultraviolet spectroscopic surveys to map out the warm tenuous gas lying in the vast cosmic filaments; and radio Sunyaev-Zel'dovich effect and X-ray surveys that reveal the distribution of the hot gas found in groups and clusters of galaxies.
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From page 53... ...
A space-based observatory to detect gravitational radiation will allow us to measure the rate at which mergers between less-massive black holes contributed to the formation process. Are the supermassive black holes we can now detect only the tip of the iceberg (the biggest members of a vast unseen population)
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From page 54... ...
The next decade of astronomical facilities should have the capability to see the effects of young planets embedded within the disks from whence they arose. Is the typical outcome of planet formation gas-giant worlds with panoplies of satellites, like Jupiter and Saturn, or rocky worlds like Earth with atmospheres and surface liquids stabi lized by being suitably near to stable parent stars like the Sun, or some completely different kind of object that is not represented in our solar system?
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From page 55... ...
on tHresHold tHe
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From page 56... ...
. Given the importance of high-mass stars to the produc tion and dispersal of heavy elements, understanding their proportion in both the benign and the more extreme star-forming environments is critical to tracking the heavy-element history of the universe.
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From page 57... ...
Galaxies and Black Holes The observable universe contains more than 100 billion galaxies, including our own Milky Way. Although we commonly think of galaxies as being made of stars and clouds of gas and dust, in fact more than 90 percent of the mass of galaxies
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From page 58... ...
This may explain why dark matter halos with low mass contain so few stars and so little gas today. The role played by the supermassive black hole is instead important for the lives of the most massive galaxies (which contain the most massive black holes)
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From page 59... ...
Two of the major goals of the coming decade are to understand the cosmic evolution of black hole ecosystems -- the intense interplay between the black holes and their environments -- and to figure out how these extremely powerful "engines" function. Black hole masses will be measured by JWST and ground-based optical and radio telescopes.
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From page 60... ...
The mass of a star has a pronounced effect on the rate at which it consumes its nuclear fuel: the more mass the star contains, the shorter its life will be (it lives fast and dies young) , and the more violent and spectacular its death, with explosive heating of the surrounding gas and production of a legacy corpse in the form of a neutron star or black hole.
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From page 61... ...
It will also depend strongly on how rapidly the star is rotating and on the strength and nature of the magnetic fields that it has built. This has far-reaching implications because the end states of massive stars (supernovae)
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From page 62... ...
Understanding stars, black holes, and gas inside and out is a central goal in astrophysics for the next decade. FIGURE 2.4.1 Left: The center of the Milky2-4-1_right hs-2009-28-g-pdf.eps wavelengths using Way galaxy observed at X-ray bitmap, w/ most type elements converted to outline, clipping masks the Chandra X-ray Observatory, at optical wavelengths using the Hubble Space Telescope, and at infrared wavelengths using the Spitzer Space Telescope.
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From page 63... ...
New stars are forming out of gas clouds concentrated in the spiral arms. A dormant supermassive black hole lurks in the bright central region.
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From page 64... ...
It is now becoming possible to study the structure and strength of magnetic fields on the surfaces of nearby stars, and changes in the magnetic fields can be diagnosed with X rays. At the same time, the major advance provided by the Advanced Technology Solar Telescope (ATST)
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From page 65... ...
Mass transferred onto the white dwarf from its companion star can trigger a runaway thermonuclear instability and explosion, providing a light show that can be seen halfway across the universe. This type of supernova event is also the most important source of iron -- from that in Earth's core to the hemoglobin in our blood -- in the universe.
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From page 66... ...
Remarkable discoveries could occur if we are lucky enough to have a galactic supernova, as the over whelming number of neutrinos from the young neutron star would provide an exciting probe of the competition between collapse and explosion going on in the inner 20 kilometers of these explosions. Even more remarkable would be to find direct evidence for gravitational wave emission from such a nearby explosion, a possibility for Advanced LIGO.
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From page 67... ...
Supernova explosions like those that left behind this source created and dispersed heavy elements and also accelerated cosmic rays. SOURCe: The HeSS Collaboration: F
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From page 68... ...
The signature of water, together with a suitable orbit around a parent star, would tell us that the medium for life as we know it is likely present as a surface liquid. Methane indicates that organic molecules (the structural building block of life)
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From page 69... ...
The last decade was one of stunning progress in our understanding of the first moments of the universe. NSF-supported South Pole and Chilean ground-based work, and NASA's balloon-based studies and the Wilkinson Microwave Anisotropy Probe Explorer mission, mapped the spatial pattern of temperature fluctuations that occur in the relic cosmic microwave background from the big bang.
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From page 70... ...
In Einstein's theory, the growth of structure and the expansion of the universe are linked by gravity; in modifications of gravity, that link is altered.5 Understanding the underlying cause of acceleration therefore requires precision measurements of the expansion of the universe with time and of the rate at which cosmic struc ture grows. Comparing the expansion history of the universe with the history of the growth of structure will in principle enable us to test whether dark energy or modifications of general relativity are responsible for cosmic acceleration.
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From page 71... ...
By now, the evidence for such dark matter in almost all galaxy-size and larger astronomical systems is overwhelming and comes from a wide variety of techniques -- among others, gravitational lensing measured by the Hubble Space Telescope and ground-based telescopes, the distribution of hot X-ray-emitting gas FIGURe 2.11 The current composition of the universe; "normal" (baryonic) matter is less than 5 percent of the total.
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From page 72... ...
, while relic copies from the early universe will be detected at high energy from their self-interactions or decay in space, producing gamma rays and other high-energy particles, and at low energy in experiments at deep-underground laboratories where rare collisions occur between normal atoms and the sea of galactic dark matter particles through which Earth swims. Already, important constraints have been set on the nature of dark matter through the failure to detect it using underground detectors and the Fermi Gamma-ray Space Telescope.
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From page 73... ...
Center: The inferred dark matter distribution in the inter acting galaxy cluster 1e 0657-56 is shown in blue, compared to the measured hot X-ray-emitting cluster gas in red and the visible light from individual galaxies in the optical image. In this classic example, the dark matter mass dominates the radiating, baryonic mass.
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From page 74... ...
In the coming decade, precise measurements of the structure seen in the CMB combined with measurements of large-scale structure from the next generation of visible/infrared imaging and spectroscopic surveys plus X-ray observations of clusters of galaxies will allow us to measure the neutrino mass or push its upper limit downward by an order of magnitude, and thereby help constrain particle physics models governing the behavior of all mass. The Nature of Compact Objects and Probes of Relativity Astronomical observations have verified that general relativity provides an accurate description of gravity on solar system scales, but an unanswered question, and the most challenging test of general relativity, is whether it works in the strong gravity fields around black holes.
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From page 75... ...
Only slightly less remarkable than black holes are the neutron stars. It is with respect to neutron stars that the investments over the last decade in ground-based gravitational wave detectors are likely to pay off first, given that frequent detections of merging neutron stars in other galaxies are expected from Advanced LIGO.
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From page 76... ...
The most rapidly rotating neutron stars appear to spin on their axes about once every 1½ milliseconds, by accreting material from a rapidly rotating disk of matter donated from a companion star. However, ever more sensitive radio pulsar surveys continue to find that the maximum spin rate observed is surprisingly less than the maximum possible value, leading to the speculative suggestion that gravitational wave emission regulates the maximum rate.
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From page 77... ...
We do not understand the ultimate levels of complexity achieved by organic chemistry in astrophysical environments, for example, whether complex information-carrying polymers like ribonucleic acid might be produced before planet formation. Study at ever more powerful spectral and spatial resolution of astrophysical environments in which organic molecules occur and evolve is necessary to trace the full potential of organic chemistry to produce molecules of relevance to life, through as much of the galaxy as is possible.
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From page 78... ...
The resulting larger molecules that are formed, such as glyco aldehyde, are ejected from the grains thanks also to the shock waves, and end up in the surrounding gas where they can be detected. The red atoms are oxygen; the grey, carbon; and the yellow, hydrogen.
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