Be an INTEGRAL astronomer: Glossary
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Binary
Pair of stars bound together by mutual gravitation, orbiting their common centre of mass.
For black hole and neutron star binary see X-ray binary.
Black hole
An object with so much mass concentrated in it, and therefore such a strong gravitational pull that nothing, not even light can escape from it. One way in which black holes are believed to form is when massive stars collapse at the end of their lives.
Calibration
The act of checking and therefore adjusting the accuracy of a measuring instrument, by comparison with a standard.
Crab nebula
A supernova remnant located in the constellation of Taurus. It was produced by a supernova explosion visible from Earth in 1054 AD. A pulsar at the centre of the nebula marks the neutron star corpse of the exploded massive star.
Electronvolt
A unit of energy equal to the amount of kinetic energy an electron gains after being accelerated through an electric potential of 1 volt in a vacuum. The electron volt is about 1.60219 × 10-19 joules. keV = 103 eV.
Flux
A measure of the amount of energy or number of particles flowing through a given area of surface in a given time. Can be measured in counts made by a detector per second or the number of photons received by a detector per square centimetre per second.
Galactic bulge
A mass of stars that forms the heart of spiral galaxies (if the shape of a galaxy is described as two fried eggs placed back to back the galactic bulge would be the yokes). (Stars that populate the bulge are normally old, Population II objects, dating back to their galaxy's earliest period. Studying bulges can therefore tell astronomers about how galaxies formed and evolved.)
Gamma ray
The most powerful form of electromagnetic radiation. A typical gamma ray is a photon with an energy greater than 100 keV.
IBIS/ISGRI
The Imager on-board INTEGRAL, or IBIS, is one of the instruments on INTEGRAL. IBIS has a wide field of view that is ideal for studying a region of the galaxy that is full of different sources, such as the Galactic Bulge.
ISGRI, or the Integral Soft Gamma-Ray Imager, is one of the detectors within IBIS. ISGRI is able to collect photons which are between 5 thousand and 5 million times more energetic than those from optical light (or light that has a wavelength between 5 thousand and 5 million times smaller than optical light).
In this competition we use data recorded by the IBIS/ISGRI at the longest wavelengths
accessible to this instrument, or equivalently, the lowest energies accessible:
all photons that are used have energies between 18 and 40 keV (the conversion from energy
in keV to wavelengths in Ångstrom is: Wavelength = 12.4/Energy).
IBIS/ISGRI does not capture images as a digital camera would because it is not possible to focus gamma rays. A complex technique (comparable to a pinhole camera) is used to image the sky however we will not go into detail here.
INTEGRAL
ESA's INTErnational Gamma-Ray Astrophysics Laboratory detects some of the most energetic radiation that comes from space. It is the most sensitive gamma-ray observatory ever launched. INTEGRAL is an ESA mission in cooperation with Russia and the United States.
Micro-quasar
An object of stellar mass that displays in miniature some of the properties of quasars. A microquasar consists of a binary system. The closest known microquasar and black hole to Earth is V4641 Sagittarii, which lies only about 1,500 light-years away.
Neutron star
An extremely dense star comprised mainly of neutrons; the endpoint of the life of a massive star which has exploded as a supernova. Under huge gravitational forces electrons have been compressed into protons and produced neutrons. A typical neutron star has about 3 times the mass of the Sun but a radius of only 10 kilometres. Fast spinning neutron stars can be observed as pulsars. If the Sun were to become a neutron star it would have a diameter of only 20 km.
Period
The time interval between two consecutive and similar phases of a regularly occurring event. For example, the period of rotation of the Earth is the time taken to complete one revolution; the period of a variable star is the time between two successive maxima or minima on its light-curve.
Pulsar
A stellar source, such as a rotating single star or pair of stars, emitting electromagnetic radiation which is characterised by rapid frequency and regularity.
Quasi-periodic
Refers to a form of motion that is regular but never exactly repeating.
Quasar
A Quasi-stellar extragalactic object; the highly energetic core of a remote active galaxy. Quasars are the most luminous objects in the Universe and capable of emitting over a trillion times as much energy as the Sun from an area that is just a little larger than the Solar System.
Supernova
Explosion of a massive star at the end of its life. Supernova explosions are so luminous that they can outshine a galaxy. There are two types of supernovae. A supernova type I is most likely a white dwarf star in a binary system which accretes material that builds up until a nuclear explosion disrupts the star. A supernova type II is a massive star which has used up all its nuclear fuel. The star then collapses and the impact of all the material produces a shock wave which blasts the outer layers of the star out.
White dwarf
A very dense star with a mass below 1.4 solar masses that is no longer burning nuclear fuel. The Sun will one day evolve into a white dwarf with a diameter of 10 000 km.
XMM-Newton (X-ray Multi-Mirror) mission
ESA's X-ray space observatory mission, with its X-ray Multi-Module design using three telescopes each with 58 nested X-ray mirrors. Named also in honour of Sir Isaac Newton. See http://sci.esa.int/xmm-newton/
X-ray
Electromagnetic radiation with wavelengths between those of ultraviolet and gamma rays, approximately 0.01-10 nm (1 nm = 10-9 m). At these short wavelengths, it is more common to talk in terms of photon energies. These energies range from 0.1-100 keV.
X-ray (hard)
Higher-energy part of the X-ray spectrum ranging from approximately 5 keV to 100 keV.
X-ray (soft)
Band of low energy X-rays, between 0.1 keV and approximately 5 keV.
X-ray binary
An X-ray emitting binary star system consists of a normal star and a compact object, such as a neutron star or a black hole. Material is stripped from the normal star by the gravitational pull of the compact object. This material is accelerated to high velocities as it spirals towards the neutron star or black hole (forming an accretion disk) and heats due to friction, to temperatures (exceeding a million degrees) hot enough for X-rays to be emitted.
In the case of a high-mass X-ray binary system a neutron star orbits around a massive star. such as a giant or super-giant.
Hence terms; Black hole binary, Neutron star X-ray binary, X-ray binary pulsar and high-mass X-ray binary.