International X-ray Observatory - AbsoluteAstronomy.com

The International X-ray Observatory (IXO) was a planned X-ray

X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

telescope from about 2008 to 2011 by NASA, ESA, and JAXA. In 2011, NASA pulled out and ESA is forking/rebooting the project as the ESA Advanced Telescope for High ENergy Astrophysics (ATHENA)., which is an L-class candidate within the ESA Cosmic Vision

Cosmic Vision

The Cosmic Vision is the paraphrasing name given to the roadmap for scientific space based missions of the European Space Agency in the time frame between 2015 and 2025....

Programme.

It was to be launched in 2021 as a joint effort by the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

space agency NASA

NASA

The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

, the European Space Agency

European Space Agency

The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...

(ESA), and the Japan Aerospace Exploration Agency

Japan Aerospace Exploration Agency

The , or JAXA, is Japan's national aerospace agency. Through the merger of three previously independent organizations, JAXA was formed on October 1, 2003, as an Independent Administrative Institution administered by the Ministry of Education, Culture, Sports, Science and Technology and the...

(JAXA). In May 2008, ESA and NASA established a coordination group involving all three agencies, with the intent of exploring a joint mission merging the ongoing XEUS

XEUS

XEUS, X-ray Evolving Universe Spectroscopy, was space observatory plan developed by the European Space Agency as a successor to the successful XMM-Newton X-ray satellite telescope...

and Constellation-X projects. This proposed the start of a joint study for IXO. IXO faced competition from two other missions, the Europa Jupiter System Mission

Europa Jupiter System Mission

The Europa Jupiter System Mission – Laplace was a proposed joint NASA/ESA unmanned space mission slated to launch around 2020 for the in-depth exploration of Jupiter's moons with a focus on Europa, Ganymede and Jupiter's magnetosphere...

(EJSM) and the Laser Interferometer Space Antenna

Laser Interferometer Space Antenna

The Laser Interferometer Space Antenna is a planned space mission to detect and accurately measure gravitational waves from astronomical sources. LISA was originally conceived as a joint effort between the United States space agency NASA and the European Space Agency...

(LISA).

Science with IXO

X-ray

observations are crucial for understanding the structure and evolution of the stars, galaxies, and the Universe

Universe

The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...

as a whole. X-ray images reveal hot spots in the Universe—regions where particles have been energized or raised to very high temperatures by strong magnetic fields, violent explosions, and intense gravitational forces

Gravitation

Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their mass. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped...

. X-ray sources in the sky are also associated with the different phases of stellar evolution

Stellar evolution

Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...

such as the supernova

Supernova

A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...

remnants, neutron stars, and black holes.

IXO will explore X-ray Universe

X-ray astronomy

X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and...

and address the following fundamental and timely questions in astrophysics

Astrophysics

Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties of celestial objects, as well as their interactions and behavior...

What happens close to a black hole?
How did supermassive black holes grow?
How do large scale structures form?
What is the connection between these processes?

To address these science questions, IXO will trace orbits close to the event horizon

Event horizon

In general relativity, an event horizon is a boundary in spacetime beyond which events cannot affect an outside observer. In layman's terms it is defined as "the point of no return" i.e. the point at which the gravitational pull becomes so great as to make escape impossible. The most common case...

of black holes, measure black hole spin for several hundred active galactic nuclei (AGN), use spectroscopy

Spectroscopy

Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...

to characterize outflows and the environment of AGN during their peak activity, search for supermassive black holes out to redshift

Redshift

In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...

z = 10, map bulk motions and turbulence in galaxy clusters, find the missing baryons

Dark matter

In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...

in the cosmic web using background quasars, and observe the process of cosmic feedback where black holes inject energy on galactic and intergalactic scales.

This will allow astronomers to understand better the history and evolution of matter and energy, visible and dark

Dark matter

In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...

, as well as their interplay during the formation of the largest structures.

Closer to home, IXO observations will constrain the equation of state in neutron stars, black holes spin demographics

Rotating black hole

A rotating black hole is a black hole that possesses spin angular momentum.-Types of black holes:There are four known, exact, black hole solutions to Einstein's equations, which describe gravity in General Relativity. Two of these rotate...

, when and how elements were created and dispersed into the intergalactic medium, and much more.

To achieve these science goals, IXO requires extremely large collecting area combined with good angular resolution

Angular resolution

Angular resolution, or spatial resolution, describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object...

in order to offer unmatched sensitivities for the study of the high-z Universe

Redshift

In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...

and for high-precision spectroscopy

Spectroscopy

of bright X-ray sources.

The large collecting area required because, in astronomy

Astronomy

Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

, telescopes gather light and produce images by hunting and counting photons. The number of photons collected puts the limit to our knowledge about the size, energy, or mass of an object detected. More photons collected means better images

Image Quality

Image quality is a characteristic of an image that measures the perceived image degradation . Imaging systems may introduce some amounts of distortion or artifacts in the signal, so the quality assessment is an important problem.-In photographic imaging:In digital or film-based photography, an...

and better spectra

Astronomical spectroscopy

Astronomical spectroscopy is the technique of spectroscopy used in astronomy. The object of study is the spectrum of electromagnetic radiation, including visible light, which radiates from stars and other celestial objects...

, and therefore offers better possibilities for understanding of cosmic processes.

IXO configuration

The heart of IXO mission is a single large X-ray

X-ray

mirror with up to 3 square meters of collecting area and 5 arcsec angular resolution

Angular resolution

, which is achieved with an extendable optical bench with a 20 m focal length.

Optics

A key feature of the IXO mirror design

X-ray optics

X-ray optics is the branch of optics which manipulates X-rays instead of visible light. While lenses for visible light are made of transparent materials that can have a refractive index substantially larger than 1, for X-rays the index of refraction is slightly smaller than unity. The principal...

is a single mirror assembly (Flight Mirror Assembly, FMA), which is optimized to minimize mass while maximizing the collecting area, and an extendible optical bench.

Unlike visible light

Visible spectrum

The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...

, X-rays cannot be focused at normal incidence, since the X-ray beams would be absorbed in the mirror. Instead, IXO’s mirrors, like all prior X-ray telescopes

Wolter telescope

A Wolter telescope is a telescope for X-rays using only grazing incidence optics. Visible light telescopes are built with lenses or parabolic mirrors at nearly normal incidence. Neither works well for X-rays. Lenses for visible light are made of a transparent material with an index of refraction...

, will use grazing incidences, scattering at a very shallow angle. As a result, X-ray telescopes

Wolter telescope

consist of nested cylindrical shells, with their inner surface being the reflecting surface. However, as the goal is to collect as many photons as possible, IXO will have a bigger than 3m diameter mirror.

As the grazing angle

Angle of incidence

Angle of incidence is a measure of deviation of something from "straight on", for example:* in the approach of a ray to a surface, or* the angle at which the wing or horizontal tail of an airplane is installed on the fuselage, measured relative to the axis of the fuselage.-Optics:In geometric...

is a function inversely proportional to photon energy, the higher-energy X-rays

X-ray astronomy

require smaller (less than 2 degrees) grazing angles to be focused. This implies longer focal lengths as the photon energy increases, thus making X-ray telescopes difficult to build if focusing of photons with energies higher than a few keV is desired. For that reason IXO features an extendible optical bench that offers a focal length

Focal length

The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus...

of 20 m. A focal length of 20 meters was selected for IXO as a reasonable balance between scientific needs for advanced photon collecting capability at the higher energy ranges and engineering constraints. Since no payload fairing

Payload fairing

Payload fairing is one of the main components of a launch vehicle. The fairing protects the payload during the ascent against the impact of the atmosphere . More recently, an additional function is to maintain the cleanroom environment for precision instruments.Outside the atmosphere the fairing is...

is large enough to fit a 20-meter long observatory, thus IXO has a deployable metering structure between the spacecraft bus and the instrument module.

Instrumentation

IXO scientific goals require gathering many pieces of information using different techniques such as spectroscopy, timing, imaging, and polarimetry. Therefore, IXO will carry a range of detectors, which will provide complementary spectroscopy

Spectroscopy

, imaging

Imaging

Imaging is the representation or reproduction of an object's outward form; especially a visual representation .- Imaging methodologies and technologies :...

, timing, and polarimetry

Polarimetry

Polarimetry is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic waves, such as radio or light waves...

data on cosmic X-ray sources to help disentangle the physical processes occurring in them.

Two high-resolution spectrometers, a microcalorimeter (XMS or cryogenic imaging spectrograph (CIS)) and a set of dispersive gratings (XGS) will provide high-quality spectra over the 0.1 – 10 keV bandpass where most astrophysically abundant ions

Interstellar cloud

Interstellar cloud is the generic name given to an accumulation of gas, plasma and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium. Depending on the density, size and temperature of a given cloud, the hydrogen in it...

have X-ray lines.
The detailed spectroscopy from these instruments will enable high-energy astronomers to learn about the temperature, composition, and velocity of plasmas

Plasma (physics)

In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

in the Universe. Moreover, the study of specific X-ray spectral features probes the conditions of matter in extreme gravity field, such as around supermassive black holes. Flux variability adds a further dimension by linking the emission to the size of the emitting region and its evolution over time; the high timing resolution spectrometer (HTRS) on IXO will allow these types of studies in a broad energy range and with high sensitivity.

To extend our view of the high-energy Universe to the hard X-rays and find the most obscured black holes, the wide field imaging & hard X-ray imaging detectors (WFI/HXI) together will image the sky up to 18 arcmin field of view (FOV) with a moderate resolution (<150 eV up to 6 keV and <1 keV (FWHM) at 40 keV.

IXO’s imaging X-ray polarimeter will be a powerful tool to explore sources such as neutron stars and black holes, measuring their properties and how they impact their surroundings.

The detectors will be located on two instrument platforms—the Moveable Instrument Platform (MIP) and the Fixed Instrument Platform (FIP). The Moveable Instrument Platform is needed because an X-ray telescopes

Wolter telescope

cannot be folded as it can be done with visible-spectrum telescopes. Therefore, IXO will use the MIP that holds the following detectors—a wide field imaging & hard X-ray imaging detector, a high-spectral-resolution imaging spectrometer, a high timing resolution spectrometer, and a polarimeter — and rotates them into the focus in turn.

The X-ray Grating Spectrometer will be located on the Fixed Instrument Platform. This is a wavelength-dispersive spectrometer that will provide high spectral resolution in the soft X-ray band. It can be used to determine the properties of the warm-hot-intergalactic medium, outflows from active galactic nuclei, and plasma emissions from stellar coronae.

A fraction of the beam from the mirror will be dispersed to a charge-coupled device

Charge-coupled device

A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...

(CCD) camera, which will operate simultaneously with the observing MIP instrument and collect instrumental background data, which can occur when an instrument is not in the focal position.

To avoid interfering the very faint astronomical signals with radiation from the telescope, the telescope itself and all its instruments must be kept cold. Therefore, the IXO Instrument Platform features a large shield that blocks the light from the Sun, Earth, and Moon, which otherwise would heat up the telescope, and interfere with the observations.

IXO optics and instrumentation will provide up to 100-fold increase in effective area for high resolution spectroscopy, deep spectral, and microsecond spectroscopic timing with high count rate capability.

The improvement of IXO relative to current X-ray missions is equivalent to a transition from the 200 inch Palomar telescope to a 22 m telescope while at the same time shifting from spectral band imaging to an integral field spectrograph.

Launch

The planned launch date for IXO is 2021, going into an L2 orbit. Studies to determine the launch vehicle, either the Ariane V or Atlas V

Atlas V

Atlas V is an active expendable launch system in the Atlas rocket family. Atlas V was formerly operated by Lockheed Martin, and is now operated by the Lockheed Martin-Boeing joint venture United Launch Alliance...

, are currently underway.

Science operations

IXO will be designed to operate for a minimum of 5 years, with a goal of 10 years, so IXO science operations are anticipated to last from 2021 to 2030.

External links

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