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INTEGRAL Observations | |
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Browse the ISDC outreach pages by clicking on the images above. Underlined words are links to a glossary (opened in a new window) allowing you to obtain complementary information. A page with links allows you to reach various sites concerning astronomy and the INTEGRAL mission.
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Index |
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The images obtained by INTEGRAL are available at Science du site de
l'ISDC.
Photos of INTEGRAL are available in our image gallery.
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The sources of our Galaxy |
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Our galaxy looked at by gamma rays
INTEGRAL regularly observes our galaxys layout (the milky way) to follow the activity of the sources of Gamma rays that are visible, the picture on the right compares the infrared emissions measured by the satellite COBE (bottom diagram) and the gamma ray emissions observed by ISGRI, the INTEGRAL imager (middle diagram and the zoom on top of that, courtesy of R. Walter and A. Bodaghee). However, the infrared image is dominated by interstellar dust heated up by stars, the gamma sky is dominated by punctual sources. The densities of the sources that are particularly big in the central region of our Galaxy
Most of the sources are Neutron stars and black holes products of a huge star exploding (supernova). Our galaxy must contain around one million black holes that only a few ten or so can be observed at a certain point.
In the gamma ray domain, the galaxy is mainly made up of neutron stars and black holes. The stars, the gas and the dust of our galaxy is invisible to these rays.
The first source discovered by INTEGRAL
On the 1st of February 2003, INTEGRAL discovered the first source surrounded by a cocoon of extremely dense gas and dust, This source was called IGR J163184-4848 (named after the tool that discovered it followed by the coordinates locating the source in the sky) and represents a new class of objects, black holes and neutron stars surrounded by gas and dust which only let threw gamma rays, all other rays being absorbed. Only INTEGRAL allows us to discover and study such sources.
This source then was managed to be seen threw X-rays by another European satellite, XMM-Newton. Both of these combined observations showed that the object seen was hidden in a cocoon of gas of a similar size to the earths orbit around the sun.
Other complimentary observations are yet to be done, with the help of European
telescopes located in chili, into the infrared and visible light so that we can
finally determine the exact nature of this source.
The black hole Cygnus X-1
The black hole Cygnus X-1 was chosen as a target for the first observation made by the satellite INTEGRAL after its launch. Its name indicates that it is the first source of X-rays discovered in the Cygnus constellation capable of observing these rays at the end of the 1960s.
The image on the right is a collection of the images obtained by the four
instruments on board the INTEGRAL, superimposed on an artists impression of the
system X-1. The artists impression represents the material being ripped from the
giant blue star (left) spiraling into a disc around the black hole (right). The
images from the INTEGRAL are from left to right, the ones taken with the gamma
ray imager (IBIS), the one taken with the Gamma spectrometer (SPI), the one
taken with the optical camera (OMC) and the one taken with the X-ray monitors
(JEM-X). All of these tools observe simultaneously the same region in the sky to
allow a detailed follow up of the spectral variations of the observed source.
Copyright ESA. Illustration by the integral team and ESA/ECF
Cygnus X-1 is a source located in our galaxy, the milky way, at a distance of about 10 000 light years away from earth. It is a binary Composing of a giant blue star 33 times bigger than the sun, and of an extremely dense and compact object with a mass of about 15 times bigger than our sun. This mass is largely to big for it to be one of a neutron star, which have a mass about 3 times bigger than our sun. So, the compact object of the binary Cygnus X-1 is very probably a black hole.
The star and the black hole form a very close bond, turning on each other in
only 5.6 days. The very strong gravitational field of the black hole rips out
some of the stars matter. This matter forms a disc around the black hole and
goes round faster the closer it gets. This matter is at the immediate merci of
the black hole, which produces X-rays and gamma rays that we observe.
The image on the left shows the region of the Milky Way where you can find Cygnus X-1 in. It only represents a very small part of the Cygnus constellation that is easily visible in Europe on a summers night. It is from a picture that does not come from INTEGRAL. The source of light (shown by an arrow) is the giant blue star very close to the black hole of Cygnus X-1. Copyright ESA & Digitized sky survey. Image processing by ESA/ECF
In the close regions of the black hole, the physical conditions produced by the gas coming from the star are extreme. The gas is heated by friction in the disc up to temperatures in the millions of degrees. The atoms dislocate themselves; the gas is ionized and becomes plasma. The fast rotation of this matter charged electrically produce immense magnetic fields, whilst the rest falls definitely into the black hole.
The gamma rays detected by INTEGRAL, tell us about what is happening in the
extremely violent world next to the black hole. This violence translates in the
observations as the rapid variations of the ray intensity from the source. The
rays are also not always emitted at the same energy level: sometimes, there are
more X-rays emitted, and sometimes more Gamma rays.
The micro quasar GRS 1915+105
One of the most fascinating sources of our galaxy is certainly the micro-quasar GRS 1915+105. It is consisted of a normal star with a similar mass to our suns that turns, in about a month, around a black hole ten times bigger than our sun.
The two celestial beings are very close. The gravitational pull from the black hole deforms the star in such ways that one of the parts of its atmosphere had collapsed into the black hole forming a disc of light. At the centre of this disc, part of the matter is ejected and forms two jets, which can be detected with the help of radio telescopes. Another part of the matter will be indulged by the black hole giving off gamma rays.
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The image on the left is from an artists impression of the system. The central
image is the image taken by INTEGRAL. The circle identifies the gamma light
coming immediately from the black hole GRS 1915+105. The figure on the right
illustrates the temporal variations of the micro-quasars observed in the X-rays
by INTEGRAL (to appear in D. Hannikainen, O. Vilhu, J. Rodriguez et al.
Astronomy and astrophysics, 2003). The astrophysicists associate the luminosity
holes with the disappearance of internal regions in the disc that could have
been swallowed by the black hole, or ejected in form of a jet. While the disc
reconstructs itself, the X luminosity results in the significant heating up of
the matter acquired.
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The diffuse emissions from our Galaxy |
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The Aluminium 26
Part of the atoms core made in the heart of the stars, some are radioactive and make some determined light by disintegrating. After the core have been ejected into interstellar space at the end of their stars life, the light emitted by their disintegration becomes visible. The detection of photons to its energies by the tools on the INTEGRAL satellite which is a recent production of these cores.
The figure underneath (to be seen in R. Diehl, J. Knoedlseder, G. Lichti, et Al. Astronomy & astrophysics 2003) shows he signature of one these events, the isotope 26 of Aluminium, detected by the spectrometer SPI on board the INTEGRAL. This radioactive element emits photons at 1809 keV and its life span is in the range of one million years. All the photons emitted by this isotope and saved by SPU come, therefore, from a heart of Aluminium 26 made by stars there is less than a few millions of years ago, which is extremely recent compared to the age of our galaxy and illustrates that the chemical elements are still in formation in the Milky way.
This Aluminium 26 is produced inside a few different types of stars in
proportions still unknown. The observation of this emission in different regions
of our galaxy and the determination of the quantity of this element present
today in each of these regions allows us to better understand the mechanics of
nucleosynthesis which operates in these stars.
The anti electrons
When an electron meets an anti electron, also known as a positron, the two
particles annihilate themselves and emit a photon at 511 keV. This becomes a
signature of this interaction.
The observations done before the launch of INTEGRAL had revealed the presence of these photons at 511 keV at the centre of our galaxy, without giving us any precise detail. The curiosity of astrophysicists was widened.
The few weeks in which the INTEGRAL passed observing the centre of our galaxy
have already permitted to have an image of the repartition of these emissions,
at the centre of our galaxy, represented in the image above (to be seen in J.
Knoedlseder, V. Lonjou, P. Jean, et al., Astronomy & Astrophysics, 2003). This
card confirms the presence of electrons and positrons at the centre of our
galaxy and reinforces the question which we ask from this observation: if the
presence of electrons in the middle of interstellar space is normal, the one of
positrons gives us a debate because there origin is unknown. The future
observations of INTEGRAL will allow us to get more clues onto how to solve this
enigma.
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The extra-galactic sources |
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The quasar 3C 273
The quasars are very luminous objects situated at great distances outside of our galaxy. These objects were found in 1963 when it was possible to precisely measure the position of things threw radio waves.
The properties of the quasars have rapidly drove the astrophysicists to explanations very far from the ones explaining the characteristics of normal stars. The very big luminosity of these objects come from the big decline in matter next to a black hole which the mass can be billions times more than the one of the sun. This matter can provoke many physical phenomena’s that gives way to radio wave emissions, infrared rays, visible rays, ultraviolet rays, X-ray and gamma rays. The biggest part of the energy seems t be given in the domain of Gamma rays, where the importance of the INTEGRAL observations come in.
The image on the right (to be seen in the Astronomy And Astrophysics, Courvoisier et al. 2003) shows one of the first observations of a quasar by INTEGRAL. This quasar is called 3C 273 because it is the 273rd object in the 3rd catalogue of radio sources edited by Cambridge. This not very poetic name is very well known by astronomers because the quasar in question is probably the best studied. Its emissions vary considerably in time. This variability is an element of utmost importance to understand the function of these objects. The quasar was particularly feeble at the moment of this observation in January 2003, some information that we would not dare to exploit when comparing the first observation with the others that the satellite will give us. This observation also shows that the emission comes well and truly from the quasar and not from the object GRS 1227+025 marked by the expansion that seems put out at this point, even though once it was much brighter than the quasar
The quasar 3C 111
Another quasar was also detected during the observations of calibrations done
on the Crab nebulous. This quasar can be found at a distance of 600 million
light ears away and is made up by a black hole about 100 million times heavier
than the sun at the centre of our galaxy. IT ejects matter in extremely powerful
jets that can be observed threw radio telescopes. The jets extend on distances
wider than the diameter of our galaxy (100 000 light years). The gamma rays of
the quasars detected by INTEGRAL is probably emitted at the base of this jet.
In the image on the right (courtesy
of M. Chernyakova and M. Turler), that shows these observations of calibration,
we can see the two sources detected by INTEGRAL, to be known that the Crab, at
the bottom left, was the target of the observation of the calibration, and the
quasar 3C 111. The image in black and white of the Crab shows the nebulous,
which is associated so that the satellite Chandra of NASA in the X-rays observes
it. The black and white image of the quasar is a radio image showing the
powerful jets of matter being ejected from the black hole at the centre of the
quasars galaxy.
The gamma bursts
An extraordinary and unpredictable event happened on the 25th of November 2002. A gamma burst happened in the region in the sky where the tools on INTEGRAL were pointing. During twenty or so seconds a rain of gamma rays reached the INTEGRAL and were captured by the imager IBIS and the spectrometer SPI on board the satellite. It’s the first time that an instrument capable of making precise images witnessed one of these mysterious occurrences.
The gamma bursts are events the most violent to watch in the universe. During a few seconds the gamma bursts shine similarly to hundreds of galaxy which themselves compose of a hundred trillion stars comparable to our sun. The first gamma bursts were discovered in the 1960s by American military satellites which mission was to detect eventual Russian nuclear tests. But its only been a few years since we have realized that these gamma bursts do not come from our solar system, nor our galaxy, but from the far reaches of the universe.
The image on the right is the first proper image of a gamma burst obtained by
the imager IBIS on board the INTEGRAL satellite. The background image is an
artists representation of the sudden explosion of a rain of gamma rays during a
few seconds. The even was detected by the INTEGRAL on the 25th of November 2002
at precisely 17h58. However, the gamma rays detected have been traveling for
about five billion years from the far reaches of the universe before reaching
the INTEGRAL Copyright: ESA. Illustration by the Integral IBIS team and ESA/ECF
Lots of different theories have been proposed to explain the gamma bursts. At this point in time, two theories seem the most correct. The bursts that lasted for a few seconds could be the explosion of a massive star at the end of its life, probably the supernova of a star that formed a black hole instead of a neutron star. The gamma bursts only lasting a fraction of a second is thought to be the formation of a black hole or a collision between two neutron stars.
The graph on the left shows the evolution of the light intensity produced by the
gamma bursts IN THE 25th of November 2002 by which it was seen by the imager
IBIS aboard the satellite INTEGRAL. The total duration of the bursts was about
20 seconds long. The image obtained by the IBIS is shown as a medallion. The
intensity of the gamma rays is represented in different colours from deep purple
to blood red. (Image courtesy: S. Mereghetti (IASF/ISDC) for the IBIS Team.
A gamma burst appears on average every two days. These events are totally unpredictable and are produced in random regions of the sky. However, the view from the INTEGRAL is relatively big, a gamma burst can be found by luck about once a month in the sight of the tools on board the INTEGRAL. The INTEGRAL has everything necessary to allow lots of progress in the observation of these mysterious explosions.
Hopefully the position of the celestial vault will be known soon, as this would
allow the observation of these phenomena with telescopes much different on earth
and in orbit. In fact, we need to measure the positions of these and disseminate
them into the international communities while the bursts are still active, all
in less than a few seconds. INTEGRAL has managed to jump an important hurdle in
this race by detecting another burst in its line of vision on the 1st of may
2003. The computers of the ISDC the automatically calculated the position of the
burst and emitted this information in less than 30 seconds after the start of
the phenomena. The robotics telescopes were then automatically directed towards
the region of the sky where the bursts appeared.
The graph on the right shows the temporary happening of the bursts and the steps
of the detection and the transmission towards the community (courtesy: S.
Mereghetti, D. Gotz et al.).
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Last updated 18 june 2008 | E-mail contact |
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