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AKARI (ASTRO-F) > Results
AKARI made a step to a key to understand the material evolution in the universe (March 2014)
A team of astronomers based at the University of Tokyo has made a significant step in better understanding the material evolution of the universe. Led by Ms Tamami I. Mori, a research fellow for the Japan Society for the Promotion of Science, the study may help to give new insights into complex carbon chemistry in the galaxy. (Details..)
AKARI Finds Carbon Monoxide Molecules Embedded in Ten Million Degree Gas (February 8, 2012)
A scientific team using the Japanese AKARI infrared space observatory finds carbon monoxide (CO) molecules in the ten million degree gas associated with the young supernova remnant Cassiopeia A (Cas A). The team is led by Dr. Jeonghee Rho, who holds a joint appointment at the SETI Institute, and at the SOFIA Science Center at NASA Ames Research Center (both located in Mountain View California). Theoretically it was neither predicted nor expected to find the carbon monoxide molecule associated with a highly energetic supernova remnant. Energetic electrons and heavy-element atoms produced by nuclear processes in supernovae should have destroyed these molecules. This finding could change our current understanding of the cycle of carbon and molecules in the interstellar gas and dust clouds. (Details..)
AKARI detected the light from the first stars (October 21, 2011)
Japanese infrared astronomy satellite AKARI measured the sky brightness at the wavelength of 1 ~ 4 micrometers and detected large spatial fluctuation that cannot be explained by the known sources. This fluctuation can be attributed to the clustering of the first stars of the universe, which were formed 300 million years after the Big Bang. The result will provide an important clue for the investigation of star formation history in the early universe for which little observational evidence has been found. The paper will be published in the November 1st issue of The Astrophysical Journal. (Details..)
Gold dust collection in the sky:
|This figure shows the distribution of 5120 asteroids detected by AKARI as of 2007 August 26.|
AKARI reveals dusty veils enshrouding two Red Giant stars with unprecedented sensitivities and accuracies. The research would help to decipher the riddle of the cosmic reincarnation of matter surrounding the mystery of the origin of the basic chemical building blocks of life such as carbon. (Details..)
|A false-color far-IR image of U Hydrae at 90 micron taken with AKARI's Far-Infrared Surveyor (FIS), showing a shell of cold dust (45 degrees Kelvin = -228 ℃).|
The latest news from AKARI project are presented. The initial version of the AKARI All-Sky Survey infrared source catalogue is now ready for scientific analysis. Three science highlights showing new insights to the activities between the old star / supernovae and interstellar media are presented from the second issue of the PASJ AKARI special issue.1. The release of the initial version AKARI infrared source catalogue
The initial version infrared source catalogue based on the AKARI All-Sky Survey is completed. The catalogue contains about three times large number of sources compared to the so far widely used IRAS (Infrared Astronomical Satellite) catalogue. The AKARI catalogue is expected to lead the future astronomical researches.(Details)
A river of the interstellar medium meanders through deep space. When stars cross these rivers, they make astronomically large splashes. AKARI, the Japan Aerospace Exploration Agency (JAXA) infrared astronomical satellite with the European Space Agency (ESA) participation, has obtained a high-resolution image of Betelgeuse; a bright red supergiant in the constellation Orion located about 640 light year from the Earth, making such a big splash as the star goes across a cosmic river.(Details)
High sensitivity far-infrared observations with AKARI confirm that interstellar space in the globular clusters is void, despite of the expectation that globular clusters contains dusts ejected from old stars within the system. Where are the dusts gone? The results left us a big mystery on the evolution of globular clusters and the interstellar dust.(Details)
AKARI has revealed unprecedented images of supernova remnants the Large Magellanic Cloud. The data shows presence of a significant amount of new, warm dust component. This implies that the efficiency of supernova remnant shocks in destroying the interstellar grains has been overestimated.(Details)
M101 is a spiral galaxy in the constellation Ursa Major lying about 24 million light years from the Earth. Its diameter is about 170 thousands light years, making M101 twice the size of our own Galaxy. Many young high-temperature stars populate the spiral arms with a remarkably giant star forming region present in the outermost arm in the galaxy. In order to investigate the star-formation activity in the galaxy we have carried out high-spatial resolution observations in all four wavelength bands of the FIS (65, 90, 140, and 160 micrometres). With these data we have been able to reveal the distribution of the the 'warm' dust heated by the young high-temperature stars in the star-forming regions, and the 'cold' dust warmed by the normal stars typical of our own Sun. (Details)
One of the most important unanswered questions in modern astronomy is how the galaxies evolved to their current form. To approach this problem it is vital to observe galaxies in the ancient era of our Universe, i.e., to observe galaxies that are very very far away. AKARI have carried out one of the most extensive observations ever made in the far-infrared wavelength range testing the ultimate performance of the FIS, and detecting many faint galaxies in the distant Universe. (Details)
The asteroid explorer Hayabusa finally departed its target, the asteroid Itokawa, in late April this year and is now heading back home to the Earth. Last month, about three months after Hayabusa's encounter, on the 26th of July, 2007, the infrared astronomical satellite AKARI also succeeded in observing Itokawa with its onboard instrument, the Infrared Camera (IRC). Figure 1 shows the image of Itokawa taken at a wavelength of 7 micrometres by AKARI. It can be clearly seen that Itokawa moves rapidly on the sky during the observation of about 12 minutes. Movie 1 demonstrates the motion of Itokawa by animation. The movie was composed using the images at two wavelengths, 7 and 11 micrometres.
|Figure 1. The asteroid Itokawa observed by the Infrared Camera (IRC) onboard AKARI at 7 micormetres. The observation was carried out at 11:23--11:35 (UT) on July 26th, 2007. We selected three images from the data taken in the observation period and composed a single image to show the motion of Itokawa over 12 minutes. The image covers roughly a 7.4 arcmin x 7.4 arcmin area around the target.|
At the time of the observation, Itokawa was in the constellation of Scorpius and was about 19 magnitudes bright in visible light. The asteroid and the Earth were closest to each other, lying at a distance of about 0.28 Astronomical Units apart (AU; 1 AU corresponds to the distance from the Earth to the Sun, about 150 million km, i.e., Itokawa was 42 million km away). Due to its proximity, Itokawa moved a significant distance on the sky over the short time of the observation. AKARI detected the target very clearly at infrared wavelengths. The asteroid is hardly visible using telescopes of similar sizes from the ground(*1).
Hayabusa itself is at a distance of around 41 million km from the Earth (it is not possible to detect it even with AKARI), and continues its journey homeward. In June 2010 after about two revolutions along its orbit around the Sun, as shown in Figure 2, Hayabusa will arrive back home to the Earth, after which time the Earth will also have made three orbits around the Sun. As of August 22nd, 2007, the spacecraft is about 50 million km away from the Earth(*2).
|Figure 2. The positions of Itokawa and the Earth at the time of the observation (July 26th, 2007) on the inertial (Zodiacal) coordinate frame. The planets and the asteroid Itokawa move along their orbits in the direction indicated. After three orbits for the Earth and two orbits for Hayabusa, the spacecraft will arrive back at the Earth in June, 2010.|
What is the meaning of this new observation of Itokawa after Hayabusa previously explored it in detail? When we study asteroids, their size is one of the most sought after pieces of information. For asteroids that are not explored directly, we can estimate their sizes based on various observations from the Earth. In fact, before Hayabusa arrived at Itokawa, many observations to determine the asteroid's approximate size had already been attempted. Among the many different measurement methods, the most accurate estimate was achieved by mid-infrared observations. This time, with AKARI, we observed Itokawa at several different wavelengths in the mid-infrared range obtaining a much more comprehensive set of data. This data is very important, not only for the study of the infrared properties of Itokawa, but also for use as a template and source of comparison with other asteroids, to improve the estimates of their sizes.
AKARI has also made observations of possible candidates for future asteroid exploration and we expect that this detailed information will help us to greatly further our knowledge of these interesting relics of our Solar System.
The observation of Itokawa was carried out as a part of the asteroids observation programme by Dr. Suano Hasegawa (ISAS&JSPEC/JAXA) and colleagues of the AKARI Solar-System Object working group.(*1) The majority of the sunlight reaching the asteroid Itokawa is absorbed on the surface, and warm ups the object. Consequently, Itokawa re-emits this heat energy as bright infrared light which was in turn observed by AKARI. On the other hand, only a small faction of the incident sunlight is reflected from Itokawa which explains why the asteroid is so very faint in visible light.
Our Galaxy is disk shaped and exhibits a spiral structure of stars. However, the stars that we see in the visible images of our Galaxy represent only a fraction of the total material of our Milky Way. In addition there are copious amounts of cold gas and dust existing at temperatures below -200 C. The distribution of this cold gas and dust is not uniform. High density regions gravitationally attracts more and more matter from the surrounding regions, until eventually stars are formed.
The emission of the cold dust and gas is invisible to us when observed in normal light, however, this material instead emits at longer wavelength infrared light. Thus, observations of the sky in infrared light can tell us where and how are this invisible gas and dust is distributed across the Galaxy. In the regions where stars are actively being formed, the dust is warmed up by the stellar light and also emits in infrared light. Therefore, by tracing this infrared emission we can search for and study the site of current active star formation in our Galaxy.
The AKARI mission is currently observing the entire sky in infrared light. This image is the All-Sky Map in the 9 micrometre wavelength range. The bright stripe seen running across the centre of the image from left to right is the disk of our own Galaxy (known as the Galactic Plane) looking from the Earth into the disk. The brightest region in the very centre of the image is towards the direction of the centre of our Galaxy. In this direction old, bright red stars crowd together adding their contribution to the infrared emission of our Galaxy in addition to that from the interstellar dust. We see several bright regions corresponding to strong infrared radiation along or next to the Galactic Plane. These regions are sites of newly born stars where we are viewing the radiation emitted from the heated dust. Note that Zodiacal emission component is crudely removed from this image.
Fig 2. Constellations and major star forming regions on the Fig 1.
(This image is produced by Nagoya City Science Museum using STELLER NAVIGATOR by AstroArts Inc.)
Nearby Galaxies and active Galactic star-forming regions appearing bright in the infrared are indicated on an identical image to Figure 1. The image tells us where in the Galaxy, stars are actively being formed. Further detailed analysis of the data used to make this image will be used to study the physical conditions of these star formation regions.
In particular, we point your attention to the object in lower-right area in the image, indicated as the "Large Magellanic Cloud". This object is in fact a galaxy that neighbours our very own Milky Way. The fact that the Large Magellanic Cloud also appears bright in the infrared implies that active star formation is also ongoing in this galaxy as well. Although they are not seen at the current resolution of this image, there are many such galaxies in the Universe undergoing active star formation. AKARI will also observe these galaxies to build up a comprehensive picture of the star formation history of the Universe.
This image covers a region of about 30x40 square degrees and includes the constellation Orion. Such a large regional image to high resolution at wavelengths beyond 100 micron is only realistically possible with an All-Sky Survey mission like AKARI. Such a survey may not be carried out again for many many years to come.
The right half of the image covers the constellation Orion, while the left side is the Monoceros. The Galactic Plane is located from the top to bottom in the left side of the image. Cold dust in the Galactic Plane appears as diffuse radiation over the entire image.
The very bright source just below the belt of Orion is the famous Orion Nebula (M42). Many stars are being born in this nebula, and the dust heated up by these stars emits very strongly in infrared light. The bright object on the left side of Orion's belt is another major star forming region which includes the Horse Head nebula. In contrast to its appearance as a dark cloud in visible light, it is extremely bright in the infrared. The bright extended emission seen in the middle-left part of the image is the so called Rosette Nebula, yet another star forming region. Finally, the big circular structure centreed at the head of Orion is clearly visible. Presumably many heavy stars were formed at the centre of the circle, Causing a corresponding series of supernova explosions that has swept out the dust and gas in the region forming a shell-like structure.
The Orion Nebula is located about 1500 light years away from the Earth and the Rosetta nebula is at a distance of 3600 light years.
An infrared image of the "Cygunus-X" region taken by AKARI. The image covers 7.6 x 10.0 square degree region in the constellation Cyguns. This region is in a direction along the so called "Orion arm", one of the spiral arms in our Galaxy. Many objects at distances of 3000--10000 light years are projected on this small region. We see the Galactic plane from the top-left to bottom-right.
The many bright spots in the image reveal regions where new stars are being born. They heat up the dust and ionize the gas in their vicinity producing strong infrared radiation. There are only a small number of regions in our Galaxy that exhibit so many massive star forming regions over such a restricted area of the sky. Large, dark hollows are also clearly visible on the image. They are created by clusters of massive, high-temperature stars, that have blow away the surrounding gas and dust by their strong radiation. Note that a similar structure was also shown previously in the image of IC 1396, presented in an earlier AKARI Gallery.
The first Japanese infrared astronomy satellite AKARI, launched in February 2006, continues observations in good condition. Further initial scientific results will be presented in the annual meeting of the Astronomical Society of Japan on the 28th - 30th of March 2007. Five selected results are explained here. On this occasion, the research concerns observations chiefly using the Near- and Mid-Infrared Camera (IRC), one of the instruments onboard AKARI.1. Star formation history revealed by AKARI wide-area survey observations
The cycle of star formation over three generations of stars was observed for the first time at seven different infrared wavelengths by AKARI. The results shed light on the process in which stars form in our Galaxy. (Details)2. The first infrared detection of a supernova remnant in the Small Magellanic Cloud
AKARI detected for the first time, a supernova remnant in our neighbouring galaxy, the Small Magellanic Cloud in the infrared wavelength from 3 to 11 micrometres, and investigated the interaction between the supernova remnant and the interstellar material. This result will be presented in the annual meeting of the Korean Astronomical Society in April. (Details)3. Stars in the later stages of their life cycle as seen by AKARI
AKARI detected evidence of high mass-loss rate from the relatively young red-giant stars based on observations from 3 to 24 micrometres. This finding provides us with new insight into to the evolution of the stars in the later stages of their life. (Details)4. Molecular gas surrounding an active galactic nucleus with a giant black hole at its centre as seen by AKARI infrared observations
AKARI has discovered evidence for molecular gas of different temperatures surrounding the active galactic nucleus containing an enormous black hole at its centre. This data will provide vital clues in understanding the structure of galaxies harbouring active galactic nuclei and black holes. (Details)5. AKARI confirms an era of intense active star formation in the Universe
The Near- and Mid-Infrared Camera (IRC) onboard AKARI has carried out a wide area deep survey in 15 micrometre infrared light, detecting many galaxies. This result indicates that a phase of intense active star formation took place in the Universe, lasting several billion years over 6 billion years ago. (Details)
|The surrounding region of the IRC4954/4955 Nebula||The supernova remnant B0104-72.3|
The Japan Aerospace Exploration Agency's (JAXA) infrared astronomical satellite AKARI continues its mission to map the entire sky in infrared light. AKARI commenced the mission's All-Sky Survey observations in May, 2006 and will finish its first coverage of the entire sky in November. The estimated completeness of the coverage at the finish of the first coverage will be about 70 percent, which is what was expected, since some areas were known not to be presently observable due to disturbances by the Moon and other reasons.
During the survey observations, AKARI investigated one of the most important targets for studies of the formation of galaxies, the Large Magellanic Cloud, with more wavelength bands than has ever been made in the past, producing stunning images of our nearest neighbour in the Universe.
AKARI obtained a far-infrared image of the Large Magellanic Cloud showing very active star formation over the entire galaxy known as a "starburst". The image reveals the dust and gas (interstellar matter) distribution over the entire galaxy. Dust grains in these interstellar clouds are heated by the light from recently born stars, and subsequently re-radiate this energy as infrared light. The infrared emission indicates that a great number of stars are currently being formed in this galaxy. Such starburst phenomena are thought to take place in many galaxies during their growth and evolution. The nature of the Large Magellanic Cloud is further revealed by the contrasting structure of the interstellar matter forming the disk-like structure and the stars that are distributed in the "spindle" shape in the lower half of the image (see also appendix). The images from AKARI show that the two components are clearly displaced from one another. Astronomers believe that the observed active star formation and the displacement of these two components in the Large Magellanic Cloud were both triggered by the gravitational force from our own Milky Way Galaxy.
The AKARI All-Sky Survey will be far superior to the previous IRAS survey mission especially in its ability to observe finer structure in the galaxy which will provide us with much more detailed information about the location and conditions of starburst. The four wavelength bands in the far-infrared range, two of which are beyond the IRAS coverage, are powerful tools to investigate the physical conditions, especially the temperature, of the interstellar clouds. Using this data we will be able to unlock the secrets of the starburst process that plays such an important role in the formation of galaxies.
In addition to the All-Sky Survey observations, AKARI also took further detailed images of a segment of the Large Magellanic Cloud at shorter near- and mid-infrared wavelengths (Figure 2). In contrast, this image shows many old stars in addition to the interstellar clouds. This image enables us to study the processes of how stars recycle and return their component gas back into the interstellar medium at the end of their lives. The unique capabilities of AKARI are again highlighted in the sheer number of stars detected in these images compared to the previous IRAS mission.
AKARI had some trouble at the beginning of the mission due to the fact that the two-dimensional Sun Sensor could not detect light from the Sun etc. Also the Star Trackers, one of the sensors for attitude control, have a problem on their cooling system. However, these problems have been successfully overcome, and now AKARI is in very good condition and continues to provide high-quality data such as the images shown here.
Figure 3. The Large Magellanic Cloud in visible light (courtesy of Mr. Motonori Kamiya) and areas of the AKARI images.
The areas corresponding to AKARI's far-infrared (Figure 1) and near- & mid-infrared (Figure 2) images are indicated by the red and green lines respectively. The far-infrared image from AKARI reveals that the interstellar clouds extend to cover the entire galaxy in contrast to the stellar distribution that is concentrated in the lower part of the image.
Figure 1 is an image of the reflection nebula IC 1396 in the constellation Cepheus taken by the Infrared Camera (IRC) in its' scanning mode. IC 1396 is located at around 3000 light years from our Solar System, and is a region where very massive (several tens of solar masses) stars are being born. Massive young stars in the central region of the image have swept out the gas and dust to the periphery of the nebula, creating a hollow shell-like structure.
Subsequent formation of the next generation of stars is also taking place within the compressed gas in these outer shell structures. AKARI has revealed for the first time, the detailed distribution of this swept out gas and dust over the entire nebula with this high resolution and quality image. Many recently born stars that were previously unknown are expected to be detected in the new image. Detailed analysis of this data will reveal the story of the star formation in this area.
Figure 2 is an image of the red giant star U Hydrae taken by the Far-Infrared Surveyor (FIS) instrument. This star is located at about 500 light years from our Sun. AKARI observations have detected very extended dust clouds surrounding this star.
Figure 3. Artist's impression of a red-giant star blowing out gas and dust.
Stars with masses close to the Sun will expand during the later stages of their lives becoming so called "red-giant" stars. Such stars will often eject gas from their surface into interstellar space. Dust is formed in the ejected gas, and this mixture of gas and dust expands out and escapes from the star. AKARI's superior quality and higher resolution image clearly detects a shell like dust cloud surrounding U Hydrae at a distance of around 0.3 light years from the central star. This image implies that a short and violent ejection of mass took place in the star some 10,000 years ago.
Appendix (PDF 312KB)
Images of the reflection nebula IC4954 taken by the two on-board instruments, the Far-Infrared Surveyor (FIS) and the near- and mid-Infrared Camera (IRC). The observed wavelengths are 90 and 9 microns, respectively. The region is at a distance of about 6000 light years and extends more than 10 light years. Star formation has been taken place in this region over several million years. In the infrared images, we can see individual stars that have recently been born. These stars are embedded in gas and dust and cannot be seen in visible light. We can also see the gas clouds from which the stars are made.
The two pictures compare the image taken by AKARI in the left and that by the IRAS satellite in the right. AKARI is able to take images with much higher resolution than the previous infrared astronomical satellites and will provide us with much more precise information about this star forming region.(Note) IRAS (InfraRed Astronomical Satellite) : The first Space mission for Infrared Astronomy by USA, United Kingdom, and the Netherlands, launched in 1983. The mission produced infrared maps of the Universe that has been used until now.
Infrared images of the galaxy M81 taken by the near- and mid-Infrared Camera (IRC). The observed wavelengths are 3, 4, 7, 11, 15, and 24 microns, respectively. M81 is a spiral galaxy at a distance of about 12 million light years from us. The images at 3 and 4 micron show the distribution of stars in the inner part of the galaxy without any obscuration from intervening dust clouds. At 7 and 11 microns we see the radiation from organic materials in the interstellar gas of the galaxy. The distribution of the dust heated by young hot stars is exhibited in the images at 15 and 24 micron, showing that the star forming regions sit along the spiral arms of the galaxy.
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