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作者:寂寞晴空塔│2019-04-13 00:07:07│巴幣:2│人氣:661

This Focus Issue shows ultra-high angular resolution images of radio emission from the supermassive black hole believed to lie at the heart of galaxy M87 (Figure 1). A defining feature of the images is an irregular but clear bright ring, whose size and shape agree closely with the expected lensed photon orbit of a 6.5 billion solar mass black hole. Soon after Einstein introduced general relativity, theorists derived the full analytic form of the photon orbit, and first simulated its lensed appearance in the 1970s. By the 2000s, it was possible to sketch the "shadow" formed in the image when synchrotron emission from an optically thin accretion flow is lensed in the black hole's gravity. During this time, observational evidence began to build for the existence of black holes at the centers of active galaxies, and in our own Milky Way. In particular, a steady progression in radio astronomy enabled very long baseline interferometry (VLBI) observations at ever-shorter wavelengths, targeting supermassive black holes with the largest apparent event horizons: M87, and Sgr A* in the Galactic Center. The compact sizes of these two sources were confirmed by studies at 1.3mm, first exploiting baselines that ran from Hawai'i to the mainland US, then with increased resolution on baselines to Spain and Chile.
這個焦點議題秀出一張相信是 M87 銀河系中心超大質量黑洞電磁輻射的超高解析度圖片。看到了一個不尋常但是清晰明亮的環,大小如同預期經過透鏡的光子軌道繞行質量大概是 65 億太陽質量的黑洞。在愛因斯坦發表廣義相對論後,理論學家導出解析形式的光子軌道,且第一次模擬的結果在 1970 年出現。在 2000 年時,就可能畫出了照片中當同步輻射從吸積盤流被黑洞重力透鏡影響的「影子」組成。在這段期間,觀察證據開始建立了銀河系中心就有黑洞的存在,而且就在地球存在的銀河系。實際上,穩定發展的無線電天文學能夠讓「超長基線干涉儀(VLBI)」在超短波長下觀測。對準超大質量且伴隨最大又明顯的事件視界 M87,和銀河系中心的 Sgr A*。第一次是在夏威夷的基線用 1.3 mm 的波長去確認這兩個來源,之後再西班牙和智利增加解析度。

Over the past decade, the EHT extended these first measurements of size to mount the more ambitious campaign of imaging the shadow itself. During 5-11 April 2017, the Event Horizon Telescope (EHT) observed M87 and calibrators on four separate days using an array that included eight radio telescopes at six geographic locations: Arizona (USA), Chile, Hawai'i (USA), Mexico, the South Pole, and Spain (Figure 2). Years of preparation (and an astonishing spate of planet-wide good weather) paid off with an extraordinary multi-petabyte yield of data. The results presented here, from observations through images to interpretation, issue from a team of instrument, algorithm, software, modeling, and theoretical experts, following a tremendous effort by a group of scientists that span all career stages, from undergraduates to senior members of the field. More than 200 members from 59 institutes in 20 countries and regions have devoted years to the effort, all unified by a common scientific vision.
在過去的幾十年,事件視界望遠鏡(ETH) 延伸的第一次看到的陰影大小。在 2017 4/5~4/11,ETH 觀測到 M87 且在不同的四天使用八個無線電望遠鏡和六個不同的地點校正,有美國亞歷桑納,智利,美國夏威夷,南極和西班牙。花了一年多處理好幾PB(1 PB = 1000 TB = 1000000 GB)的資料。這些資料在這裡呈現,從觀測圖片到解釋,議題從團隊儀器,演算法,軟體,模型和理論專家,還有許多不同年齡的科學家,從大學生到資深人員。超過 20 個國家,59 個機構,200 位成員一起貢獻了幾年,最後統一成一個共同的科學觀點。

Focus on EHT
Figure 2. A map of the EHT. Stations active in 2017 and 2018 are shown with connecting lines and labeled in yellow, sites in commission are labeled in green, and legacy sites are labeled in red. From Paper II (Figure 1).

The sequence of Letters in this issue provides the full scope of the project and the conclusions drawn to date. Paper II opens with a description of the EHT array, the technical developments that enabled precursor detections, and the full range of observations reported here. Through the deployment of novel instrumentation at existing facilities, the collaboration created a new telescope with unique capabilities for black hole imaging. Paper III details the observations, data processing, calibration algorithms, and rigorous validation protocols for the final data products used for analysis. Paper IV gives the full process and approach to image reconstruction. The final images emerged after a rigorous evaluation of traditional imaging algorithms and new techniques tailored to the EHT instrument--alongside many months of testing the imaging algorithms through the analysis of synthetic data sets. Paper V uses newly assembled libraries of general relativistic magnetohydrodynamic (GRMHD) simulations and advanced ray-tracing to analyze the images and data in the context of black hole accretion and jet-launching. Paper VI employs model fits, comparison of simulations to data, and feature extraction from images to derive formal estimates of the lensed emission ring size and shape, black hole mass, and constraints on the nature of the black hole and the space-time surrounding it. Paper I is a concise summary.
這一系列的論文提供了全部的專案範圍和目前至今的結論。論文 II 是對於 ETH 陣列的描述,這個技術發展開啟了先導探測,和全部範圍的報告。在目前已存在的機構部屬這些先進的儀器,這些合作創造了獨特的功能,能拍到黑洞的新望遠鏡。論文 III 是給最後分析資料的詳細觀測結果,資料處理,校正演算法,和嚴格的驗證協定。論文 IV 給出了重建圖片所有的處理跟方法,最後的圖片在使用傳統的圖片和給 ETH 量身訂做的演算法(伴隨著許多合成的資料集,並且花了好幾個月測試演算法)嚴格評估後出現。論文 V 使用新的廣義相對論礠流體組合函式模擬和先進的光路追跡去分析黑洞吸積盤和他的噴流圖片與資料。論文 IV 使用模型擬和,相較於模擬資料,從圖片中的特徵萃取到推導正式估算透鏡效應環的大小與形狀,黑洞質量和自然界中黑洞還有時空環境的限制,最後論文 I 給出了簡潔概述。
Our image of the shadow confines the mass of M87 to within its photon orbit, providing the strongest case for the existence of supermassive black holes. These observations are consistent with Doppler brightening of relativistically moving plasma close to the black hole lensed around the photon orbit. They strengthen the fundamental connection between active galactic nuclei and central engines powered by accreting black holes through an entirely new approach. In the coming years, the EHT Collaboration will extend efforts to include full polarimetry, mapping of magnetic fields on horizon scales, investigations of time variability, and increased resolution through shorter wavelength observations.
我們圖片畫出了 M87 的光子軌跡的邊界,提供了最強的超大質量黑洞存在的例子。這些觀測與相對論性電漿在黑洞透鏡附近的光子軌跡移動所產生的嘟普勒增亮一致,他們增強了活躍星系核和藉由中心引擎-黑洞吸積-的驅動的連結。在未來的幾年中,ETH 合作會拓展效能到偏振,映射磁場到世界尺度,調查時間變化性,和利用更短波長增加解析度。
In short, this work signals the development of a new field of research in astronomy and physics as we zero in on precision images of black holes on horizon scales. The prospects for sharpening our focus even further are excellent.
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