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Birth, death and rebirth: AKARI sees life-cycle of Stars in a new light

Scientists using the AKARI infrared satellite, launched in 2006, are releasing their initial results at a conference on March 28th–30th. AKARI has shed new light on both the birth and death of stars and galaxies, phenomena that take place in dusty areas of the Universe and can best be studied in the infra-red.

The new results show the intimate connection between star death, which releases material into the interstellar medium (the collection of dust and gas between stars and galaxies), and star birth which gathers up that material.

The AKARI team members at Imperial College, Open University, University of Sussex and University of Groningen are contributing to the data analysis of AKARI’s all-sky survey, and contributed to the science of some of these first results.

Dr. Stephen Serjeant (Senior Lecturer in Astrophysics at the Open University) said, “In the deep cosmological survey, AKARI sees the signature of organic molecules in distant redshifted galaxies. These galaxies are in their birth-throes, and this exceptionally sensitive survey with AKARI’s superb wide-field camera tells us great deal about the star formation during the birth of galaxies like our own, and their subsequent evolution. AKARI has also shown very clearly how one star can trigger then next generation of new stars in our own Galaxy. Having spent so many years working on this mission, I’m absolutely thrilled to see the first science from AKARI.”

Peter Barthel (professor of astronomy at Groningen University, The Netherlands) said, "AKARI will for the first time permit assessment of the far-infrared energy output of many classes of active galaxies, quasars and starburst galaxies. These very energetic objects were much more numerous in the early - that is distant - universe, and so far our knowledge of these objects was rather limited. AKARI will hence increase our understanding of the early phases of the Universe, in which the galaxies such our own Milky Way were being formed and shaped."

New results are being presented at the conference, with five highlights showing:
- Evidence for three generations of continuous star formation in a nebula, each dependent on the preceding generation, which will allow detailed study of the processes by which stars form. The distribution of material in the interstellar medium is clearly compacted by parent starts, making nurseries where new stars are born.

- The first ever infra-red observations of a supernova remnant in our galactic neighbour, the Small Magellanic Cloud, giving a detailed study of how material ejected in supernova events interacts with the surrounding interstellar medium and supplies it with heavy elements formed in star cores.

- First ever observations of red-giant stars being in the earlier evolutionary stage losing large amounts of matter into the interstellar medium. This mechanism had been theoretically predicted as the means by which stars that are too small to undergo supernova (such as our Sun) end their lives. Previous observations had only ever seen this process in red-giants in their last stage, AKARI has observed in it younger stars and seen evidence that this is a sporadic process that stars go through once they enter the red giant phase.

- Processes at the heart of an active galactic nucleus. These are compact areas in the centre of galaxies that radiate very brightly. They are thought to contain massive black holes which drive these processes. AKARI has looked inside the heart of one such galaxy, hidden to other telescopes by a thick interstellar medium, and seen the signature of carbon monoxide in the vicinity of the central black hole.

- AKARI made a deep cosmological survey, sensitive to the characteristic emission from organic material in the interstellar medium of distant star-forming galaxies. Previous surveys showed that the Universe underwent a period of intense star formation 6 billion years ago (when our own Sun formed). AKARI’s survey is ten times bigger than these previous surveys, and finds evidence that this busy spell started even earlier than that.

Professor Keith Mason, CEO of PPARC which funds UK involvement with AKARI, said “AKARI is a prime example of British scientists collaborating with international partners in cutting-edge research. This Japanese-led mission is peering through the cosmic dust of the Universe in unprecedented detail to reveal just how stars are born and die.”

Dr. David Clements (postdoctoral research fellow at Imperial College London) said, “AKARI is once again demonstrating the real power of infrared astronomy, with scientific impact at all stages of stellar evolution, in the early life of galaxies, and at the cores of the most energetic objects in the universe. From black holes to young stars infrared astronomy is the key, and AKARI is doing a great job at unlocking these secrets.

Professor Glenn White (The Open University and the CCLRC Rutherford Appleton Laboratory) said: "Observations of the IRC4954/4955 region spectacularly show how one generation of young stars can spawn the next. The bright nebulosity lies at the edge of a cavity, which is blown out by the radiation and winds of the first generation of young stars. This sweeping up process drives shock waves into the surrounding gas, forcing it to collapse under its own gravity, forming the next generation of young stars. Observations of the large scale processes involved in star formation are only now becoming available to observations such as those of the AKARI satellite, because of the exceptional stability and wide area coverage at infrared wavelengths. One of the main objectives in the coming months will be to use the all-sky survey to build a galaxy wide perspective on the processes important to star formation using similar data"

Dr. Chris Pearson (European Space Agency Support Astronomer to the AKARI mission, ISAS, Japan) said, "Almost one year since it opened its eye on the infrared Universe, we are now enjoying the fruits of AKARI’s observations. These images in particular demonstrate the unique multi wavelength coverage of AKARI that enables us to dig deeper into the details hidden within our images of the Universe."

Dr. Seb Oliver (Acting Director of the Astronomy Centre at University of Sussex) says. "These new results from the latest infrared mission underline the importance of infrared telescopes in astronomy. For every photon [particle of light] detected by an ordinary optical telescope on Earth another was absorbed by dust and produced infrared photons. A full understanding of quasars and star-formation will only be possible when we understand what happened to all these photons"

Julia Maddock | alfa
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