スターバースト (No. 826)
date 2023 06 08 --------------------------- 雨水によって山が削られ、川によって運ばれた土砂で平野ができます。 滴る水で岩が削られるように、 小さなことが長年積み重なって大きなものが作り出されるとうイメージがあるのでないでしょうか。 それが自然現象だと。 しかし、このイメージは少し違うかもしれません。 例えば河原に出ると大小様々な小石や岩がごろごろしていますが、 日常見ている川の流れでは到底これらの石や岩は上流から運ばれるとは考えられません。 何年、何十年に一度という大雨、洪水がなせる技です。 実は小さなことが積み重なっているのではなくて、 たまに起こる大事件が自然の変化を作ると言った方が良さそうです。 宇宙にはたくさんの星があります。 宇宙の星も少しづつ長い年月をかけて生まれたというわけではなくて、 たまに起こる大事件が重要なようです。 図１は、ジェイムズ・ウエッブ宇宙望遠鏡で撮影されたNGC4449という銀河です。 1250万光年という銀河としては比較的近い距離にあります。 ちょうど今、よく見える位置にいます。 図2の麦星と麦星を指し示す３つの星が作る円弧の中、 りょうけん座という場所にあります。 肉眼では見えませんが、最近普及してきた電子式のカメラ望遠鏡だと写ると思います。 この銀河は私たちの住む銀河よりもずっと小さい銀河で、 もう一つ別の小さい銀河と衝突したようです。 小さい銀河が衝突、合体して大きな銀河ができていきます。 このような衝突が引き金になって一気に何億という星が爆発的に誕生します。 天文学の用語では、爆発的星形成あるいはスターバーストと呼んでいます。 中心に多い青く見える部分は銀河の星々で、 オレンジや赤に見える部分が爆発的に星を作っているガスです。 周辺部で白く見えているところでは星団が作られています。 このような爆発的星形成を繰り返しながら宇宙の星の数は増えていったのです。
図1 爆発的星形成をしている銀河NGC4449 (提供：ESA/Webb, NASA & CSA, A. Adamo (Stockholm University) and the FEAST JWST team) http://www.shibatashinpei.jp/lib/yamashin/826-fig1.jpg
図2 NGC4449の位置 http://www.shibatashinpei.jp/lib/yamashin/826-fig2.jpg
本文終わり (homeへ)
パワポ http://www.shibatashinpei.jp/lib/yamashin/826-fig.pptx references below Featured in this new image from the NASA/ESA/CSA James Webb Space Telescope is the dwarf galaxy NGC 4449. This galaxy, also known as Caldwell 21, resides roughly 12.5 million light-years away in the constellation Canes Venatici. It is part of the M94 galaxy group, which lies close to the Local Group that hosts our Milky Way. NGC 4449 has been forming stars for several billion years, but it is currently experiencing a period of star formation at a much higher rate than in the past. Such unusually explosive and intense star formation activity is called a starburst and for that reason NGC 4449 is known as a starburst galaxy. In fact, at the current rate of star formation, the gas supply that feeds the production of stars would only last for another billion years or so. Starbursts usually occur in the central regions of galaxies, but NGC 4449 displays more widespread star formation activity, and the very youngest stars are observed both in the nucleus and in streams surrounding the galaxy. It's likely that the current widespread starburst was triggered by interaction or merging with a smaller companion; indeed, astronomers think NGC 4449's star formation has been influenced by interactions with several of its neighbours. NGC 4449 resembles primordial star-forming galaxies which grew by merging with and accreting smaller stellar systems. Since NGC 4449 is close enough to be observed in great detail, it is the ideal laboratory for astronomers to study what may have occurred during galaxy formation and evolution in the early Universe. This new image makes use of data from two of Webb’s instruments: MIRI (Mid-InfraRed Instrument) and NIRCam (Near-InfraRed Camera). Observations in the infrared reveal the galaxy’s creeping tendrils of gas, dust and stars. The bright blue spots reveal countless individual stars, while the bright yellow regions that weave throughout the galaxy indicate concentrations of active stellar nurseries, where new stars are forming. The orange-red areas indicate the distribution of a type of carbon-based compounds known as polycyclic aromatic hydrocarbons (or PAHs) — the MIRI F770W filter is particularly suited to imaging these important molecules. The bright red spots correspond to regions rich in hydrogen that have been ionised by the radiation from the newly formed stars. The diffuse gradient of blue light around the central region shows the distribution of older stars. The compact light-blue regions within the red ionised gas, mostly concentrated in the galaxy’s outer region, show the distribution of young star clusters. NGC 4449 was observed by Webb as part of a series of observations collectively titled Feedback in Emerging extrAgalactic Star clusTers, or FEAST (PI: A. Adamo). Two other targets of the FEAST programme, M51, and M83, were the subjects of previous ESA/Webb Picture of the Month images in 2023. [Image Description: A close view of the central area of a dwarf galaxy. A huge number of stars fill the whole galaxy as tiny glowing points. They are brightest around the galaxy’s shining core. Thick clouds of gas and dust billow out across the scene, curling like moving flames. They glow in warm colours following their location: orange around the galaxy’s core, and around glowing star clusters in the bottom-left, and dark red elsewhere.] Links NGC 4449 (NIRCam image) NGC 4449 (MIRI image) Slider tool: Webb’s MIRI and NIRCam images of NGC 4449 Slider tool: Hubble and Webb’s views of NGC 4449 Video: Pan of NGC 4449 (NIRCam+MIRI image) Video: Pan of NGC 4449 (NIRCam image) Video: Pan of NGC 4449 (MIRI image) Transition video: Webb's views of NGC 4449 Transition video: Hubble and Webb's views of NGC 4449 Credit: ESA/Webb, NASA & CSA, A. Adamo (Stockholm University) and the FEAST JWST team Usage of ESA/Hubble/Webb Images and Videos Are you a journalist? Subscribe to the ESA/Hubble/Webb Media Newsletter. About the Image Id: potm2405a Type: Observation Release date: 29 May 2024, 14:00 Size: 5249 x 3093 px
