Current Status of the AKARI Mission After one year of observations --- The Universe as seen by AKARI
Japan Aerospace Exploration Agency (JAXA)
The infrared astronomy satellite AKARI started the regular observations in May 2006. In the last one year, AKARI has carried out the All-Sky Survey observations to map the entire sky, as well as thousands of pointed observations of selected targets. Here we show the beautiful images constructed from the AKARI All-Sky Survey data; The entire sky in the mid-infrared light, the far-infrared image of the constellation Orion and the Milky Way, and the far-infrared image of the Cygnus-X region.
The Infrared Astronomy Satellite AKARI
- The first Japanese infrared dedicated astronomical mission
- Sun-synchronous polar orbit, Altitude ~ 700 km
- Length 3.7m, Launch weight 952 kg
- A reflection telescope of 68.5 cm diameter cooled by liquid Helium and mechanical coolers
- Objective: All-Sky Survey in infrared light. Investigating the birth and evolution of galaxies, stars and planets.
- February 21st, 2006 (UT): Launched by the 8th M-V (Mu-five) rocket
- April 13th, 2006: Aperture Lid Opening, First light
- May 8th, 2006: Scientific observations started
- Nov, 2006: Completed the first round survey observation
The AKARI Project is carried out with the participation of mainly the following institutes; Nagoya University, The University of Tokyo, National Astronomical Observatory Japan, European Space Agency (ESA), Imperial College London, University of Sussex, The Open University (UK), University of Groningen / SRON (The Netherlands), Seoul National University (Korea). The far-infrared detectors were developed under collaboration with The National Institute of Information and Communications Technology.
Current status and achievements of AKARI
- One year after the beginning of scientific operations in May 2006, AKARI continues observing.
- All-Sky Survey observations in six wavelength bands.
- More than 90 % of the entire sky has been observed twice.
- At least two observations are required for the reliable detection of infrared sources
- Observations are continuing in order to cover the regions not yet observed twice.
- The first census of the infrared sky since the atlas made by IRAS 24 years ago with improved spatial resolution.
(IRAS: The first infrared astronomy mission launched in 1983 by U.S., the Netherlands, and the UK)
- More than 90 % of the entire sky has been observed twice.
- Pointed observations (10 minute exposure of a given position on the sky to make detailed observations)
- About 3500 pointings in the first year
- Two large-area deep legacy surveys in the North Ecliptic Pole and the Large Magellanic Cloud regions
- 15 core observation programmes dedicated to the study of zodiacal light, interstellar matter, star and planet formation, stellar evolution, active galactic nuclei/infrared luminous galaxies and infrared background radiation
- A portion of the observing opportunities is open to the general astronomical community in Japan, Korea and ESA affiliated countries for Open Time observations
- About 3500 pointings in the first year
Near future plan
- Observations at cryogenic temperatures with liquid Helium (with all instruments) are expected to continue until at least early September 2007.
- We are considering to continue observations beyond the liquid Helium boil off with the near-infrared instrument (covering 2--5 micrometres) using the mechanical coolers.
The universe as seen by AKARI All-Sky Survey
Figure 1. The entire sky as seen in infrared light at 9 micrometres
This image is created from the data taken by one of the onboard instruments, the Near- and Mid-Infrared Camera (IRC). The centre of our Milky Way Galaxy is located at the centre of the image. The bright region extending from left to right is the Milky Way. The interstellar dust is heated by the stellar light and radiates infrared light. The data used to create this image have a spatial resolution of about 9 arcseconds, several times finer than the previous IRAS survey. AKARI also carries out the All-Sky Survey in the additional 18, 65, 90, 140, and 160 micrometre wavebands.
Figure 2. Constellations and dark clouds actively forming stars are indicated on the same 9 micrometre all-sky image.
Figure 3. The constellation Orion and the Milky Way in the winter sky at the wavelength of 140 micrometres
Images in the visual light (left) and the infrared light (right) are compared. This image covers a sky area of 40 degrees in the vertical direction. Dust grains in high-density molecular clouds are heated up by the newly born stars and emit strong infrared radiation. This is the first image of the Orion region at infrared wavelengths longer than 100 micrometres at such fine resolution.
Figure 4. The star forming regions in the constellation Cygnus (false colour composite from 90 and 140 micrometres)
One of the brightest regions in the Milky Way seen in infrared light (see Figure 1 and 2). Many massive stars are being formed. The image covers 10 degrees in the vertical direction. This is the first image of this region at infrared wavelengths longer than 100 micrometres. The images are constructed from the AKARI data by Dr. Daisuke Ishihara (Univ. of Tokyo, Figure 1 & 2) and Dr. Yasuo Doi (Univ. of Tokyo, Figure 3 & 4)
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.
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
July 11, 2007