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IXO is a relatively new mission concept. Do you have questions? Contact us using the links provided on our Contact Us page.
A: High-energy phenomena - particularly in the X-ray band - characterize the evolution of cosmic structures on both large and small scales. On the smallest scales, X-rays provide the only electromagnetic spectral signatures from the regions of strong gravity near black holes and neutron stars. X-rays from these energetic processes penetrate absorbing gas carrying spectral and timing signatures that allow us to uncover the earliest massive black holes. On the largest scales, X-rays are indispensable for detecting the "missing" 50% of baryons in the local Universe, and as a probe of both dark energy and dark matter. Thus, the X-rays qualify as a key, vital window to study the Universe, complementing and augmenting studies at the other wavelengths.
A: The International X-ray Observatory (IXO) is a new X-ray telescope with joint participation from NASA, the European Space Agency (ESA), and Japan's Aerospace Exploration Agency (JAXA). The launch date of IXO will depend on the outcome of the Astrophysics Decadal survey - which will be announced in the summer of 2010. Based on the NASA, ESA, and JAXA budgets, the earliest would be ~2020. The mission will be designed to operate for a minimum of 5 years, with a goal of 10 years. IXO will address many timely and key questions confronting astrophysics such as: How do supermassive black holes grow and evolve? How does galaxy cluster evolution constrain the nature of dark matter and dark energy?
A: The basic answer is that IXO has a much larger collecting area and improved spectral resolution than previous X-ray observatories. However, both these properties are highly dependent upon energy, so the real answer is included in the plots below showing the effective area (collecting area of the mirror convolved with the quantum efficiency of the relevant detectors, etc.) and the spectral resolution of the various IXO focal instruments compared with current missions.
| Effective Area Plot | Resolution Plot |
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A: The bumps and edges in the effective area curve appear because of resonance scattering and (or) absorption of X-rays which have energies near the M shell of the X-ray mirror reflecting material which in this case is iridium.
The simplest Rutherford-Bohr model depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus. According to this model, the electrons can only circle in specific orbits. Each orbit is characterized by a certain discrete distance from the nucleus and specific energy.
When the X-rays hit the reflecting material, the oscillating electric field of the electromagnetic radiation interacts with the electrons bound in an atom. There are two types of possible interactions – the radiation either will be scattered by these electrons, or it will be absorbed and excite photoelectrons. At certain energies the absorption increases dramatically and gives rise to an absorption edge. Each edge occurs when the energy of the incident photon is just sufficient to cause excitation of a core shell electron of the absorbing atom to a continuum state, i.e. to produce a photoelectron. The energies of the absorbed radiation at these edges correspond to the binding energies of electrons in the K, L, M, etc., orbits of the absorbing atom.
Scattering occurs due to the electron transitions from the core level to the higher unfilled or half-filled orbital (e.g., s -> p, or p -> d).
As a result, the original photon is lost and other secondary photons with very difference energies may be emitted by the atom. When this happens, the X-ray mirror has a relatively low reflectivity, but the detector has relatively high quantum efficiency. Because these are resonances, they appear as rather discontinuous jumps in the effective curve. If the effective area curve has taken into account not only the X-ray mirror, but also the calorimeter windows and absorbers, there will be even more bumps and edges. These bumps and edges are related to resonance scattering and (or) absorption of X-rays in those materials, such as aluminum, gold, or bismuth.
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A: This depends on your perspective. The IXO efforts have been underway for more than a decade as the independent projects of Constellation-X and XEUS. However, as a unified vision, the project has been under development since May 2008.
A: Virtually every phenomenon in the sky requires a panchromatic view to be fully understood. This is because the various wavelengths provide windows on different processes and components of the source, and only by considering all the pieces of information together can astronomers hope to capture the fundamental physical processes at work. With its large collecting area and improved spectral resolution, IXO will complement and augment planned future ground- and space-based observatories such as JWST, E-ELT, TMT, ALMA, and others, in shedding light on the most energetic processes at work in the heart of galaxies, on primordial black holes and their connection to forming structures, and on the mysterious "dark" components of the Universe. Indeed, IXO's science drivers are the same as those of the other Great Observatories, ensuring future synergy and commonality of scopes.
A: IXO will address a variety of science questions in a wide range of topics from stars to quasars, from galaxies and black holes to dark energy and planet formation. In particular, IXO will be able to gather the signals from black holes at the early stages of the Universe, and study their connection and co-evolution with primordial galaxies. Matter under extreme conditiones, such as in the deep potential wells of supermassive black holes or in the core of neutron stars, will be one of the primary themes for IXO, as well as the origin and content of our Universe, and study of how elements are created and dispersed in the Universe via stars and cosmic explosions and accelerations.
A: There are many new technologies that will make IXO a quantum jump from the current X-ray observatories. To allow for the order of magnitude jump in telescope size requires the development of new ultra-light X-ray optics. Two different technologies are being pursued. In Europe the silicon wafers used to for micro-processor chips and in the US the glass used for laptop screens are being shaped to the correct figure so as to form the required shape. The detectors will all use new technologies that are under development.
Micro-calorimeter arrays operate at 50mK (a hair above absolute zero) and sense the heat deposited when an X-ray is absorbed. These will be the work horse devices, that both image and provide high spectral resolution (similar to integral field spectrometers in the optical). A wide field imager will utilize active pixels to provide CCD spectral resolution, but will be immune to radiation damage and have fast readout times (and will also provide a high time readout for bright sources). New light weight gratings will provide higher spectral resolution and higher efficiency than the Chandra and XMM gratings. And finally new devices to sense the X-ray polarization from Cosmic X-ray sources will open a whole new window on the X-ray universe.
There are many pressing science questions that require observations of the hot universe, that can only be made with X-ray telescopes. These include the origin and evolution of Black Holes, the cause of the accelerating Universe, the formation of large scale structure, the equation of state of Neutron Stars. All these and many other topical questions require an X-ray telescope with an order of magnitude more area. The technology development over the past decade combined with he detailed mission studies means that the IXO mission can be ready to be launched around 2020. It will join the other major observatories that cover other wavebands such as JWST, HST, Fermi and ALMA to bring a multi-wavelength solution to the many puzzles and problems confronting modern astrophysics.
X-rays do not penetrate the Earths atmosphere and the only way to observe the X-ray Universe is to place X-ray telescopes on spacecraft. The whole field of X-ray astronomy was enabled by the space race in the 1960s, and has grown to be now a major branch of astronomy.
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