BETTII - the Balloon Experimental Twin Telescope for Far Infrared Interferometry

自大爆炸以来，宇宙中产生的一半以上的能量现在以电磁辐射的形式存在于光谱的远红外部分——波长比可见光长几百倍。发展中的恒星和年轻恒星发出的大部分能量被它们形成的气体云和尘埃云吸收，并以远红外的形式重新辐射出去。因此，如果我们想了解今天银河系中恒星的诞生过程，或者研究星系是如何成长和发展的（通过恒星形成），我们需要在远红外波段进行观测。近年来，太空望远镜和高空气球在我们努力获取恒星和行星系统形成细节以及银河系等星系历史的知识方面取得了巨大进展。但是远红外波段的天文学还有很长的路要走，我们才能在较短波长的光学望远镜和较长波长的射电望远镜阵列上拍摄出类似质量的照片。观测必须从太空或高空进行，因为大气对光谱的这一部分有很强的吸收作用。这使得使用大型地面望远镜变得困难。此外，用于射电领域的“干涉测量”技术，即将来自许多小型望远镜的光束组合在一起，使图像与来自大型望远镜的图像一样好，但在远红外领域尚未完善。因此，目前，远红外线观测的图像质量远不如天文学家更好地观察恒星和星系及其起源所需要的那样好。在这个项目中，我们将通过建造第一个在远红外波段工作的科学干涉仪，在高空气球上飞行，并对我们银河系中的恒星形成区域以及在其中心藏有大质量黑洞的活动星系进行观测，以进一步了解恒星如何在星团中形成以及黑洞如何与它们所居住的星系相互作用，从而取得重大进展。这些开创性的测量将是有史以来质量最高的远红外观测，就我们在图像中识别精细细节的能力而言。除了给我们提供新的科学见解外，它们还将使我们能够完善和展示所需的技术，以便在未来建造一个更雄心勃勃、更强大的仪器，也许是一个太空系统，以提供更好的观测。美国国家航空航天局和欧洲航天局都认识到这样一个天文台在科学上的重要性，他们正在考虑这类太空任务。然而，目前还没有必要的技术和专门知识，这项工作将对建立我们执行这种任务的能力作出重大贡献。

More than half of the energy generated in the Universe since the big bang now exists in the form of electromagnetic radiation in the far infrared part of the spectrum - wavelengths a few hundred times longer than those of visible light. Much of the energy emitted by developing stars and young stars is absorbed by the clouds of gas and dust in which they form, and re-radiated in the far infrared. So if we want to understand the birth processes of stars in our own galaxy today, or to investigate how galaxies grow and develop (through star-formation), we need to make observations in the far infrared. In recent years, huge advances have been made by telescopes in space and operating on high altitude balloons in our endeavours to gain knowledge of the details of star and planetary system formation and the history of galaxies like our own Milky Way. But astronomy at far infrared wavelengths has a long way to go before we will be able to take pictures with similar quality to that obtained by optical telescopes at shorter wavelengths and by arrays of radio telescopes at longer wavelengths.Observations have to be made from space or from high altitude because the atmosphere is strongly absorbing in this part of the spectrum. That makes it difficult to use large ground-based telescopes. In addition, the technique of "interferometry", used in the radio region of combining the beams from number of smaller telescopes to make an image as good as that from a much larger one, has not yet been perfected in the far infrared. So at present, the image quality of observations in the far infrared is not nearly as good as astronomers need to get a better view of stars and galaxies and their origins. In this project we will make a big advance by building the first scientific interferometer working in the far infrared, flying it on a high altitude balloon, and making observations of both of star forming regions in our galaxy and also of active galaxies harbouring massive black holes at their centres, to learn more about how stars form in clusters and how black holes interact with the galaxies they inhabit. These pioneering measurements will be the highest quality far infrared observations ever, in terms of our ability to discern fine details in the image. Besides giving us new scientific insights, they will allow us to perfect and demonstrate the technology needed to build a more ambitions and powerful instrument in the future, perhaps a space-borne system, to provide even better observations. The scientific importance of such an observatory has been recognised by both NASA and by the European Space Agency, who are considering space missions of this type. However, the necessary technology and expertise is not available yet, and this work will make a big contribution to establishing our capability to fly such a mission.