鬼吹灯之牧野诡事

NASA IXPE结果有助于揭开超新星爆炸的秘密_我的网站

A |     IXPE于2021年12月9日发射，由NASA和意大利航天局合作，是第一个能以这种敏感度和清晰度测量X射线光偏振的卫星。它旨在发现宇宙中一些最极端天体的秘密--超新星爆炸的残余物、由进食黑洞吐出的强大粒子流等。

B |     Dozens of businesses, government offices, vehicles, and at least three police stations went up in flames in Freetown, Makeni, Kamakwie, and other cities across Sierra Leone from August 10 through 12, with over 113 people arrested and police introducing an emergency nationwide curfew and deploying tear gas and live ammunition to disperse crowds.,The curfew was lifted on August 13, with banks, businesses, government offices, and most stores reopened and communal services beginning to clear the damage. However, ramped-up security measures, including federal troop deployments to assist police, have been left in place.,What Happened?,Sierra Leone is one of the poorest nations in the world, ranking 186 out of 198 in a recent GDP purchasing power parity ranking. An estimated 80 percent of the population lives in poverty, many of them in the country’s rural areas. Like other nations in Africa, the country has faced special difficulties amid the global economic calamity brought on by COVID, and exacerbated by Western restrictions on Russian exports of agricultural goods and fertilizers amid the security crisis in Ukraine, which has caused a major jump in food prices.,AfricaAnti-Russia Sanctions Left Africa Without Access to Grain and Fertilisers, African Union Chief Says3 June, 11:13 GMT,As a net importer of both energy and food, Sierra Leone is especially vulnerable to global economic conditions, and along with food and fertilizers, fuel and electricity costs have also soared. Food prices alone have jumped by over 40 percent over the past few months, with a bag of rice once costing 350 leones now going for over 500. The country’s Central Bank recently removed three zeros from the national currency in a bid to restore confidence. The country has also been overcome by weeks of strikes by government workers, including doctors and teachers, and by small traders protesting poor conditions.,Coup Plot?,However, President Julius Maada Bio has also accused protesters of having ulterior motives beyond the cost of living crisis.,“This was not a protest against the high cost of living occasioned by the ongoing global economic crisis. The chant of the insurrectionists was for a violent overthrow of the democratically-elected government,” Bio said in an address on August 12 after returning to the country from a holiday in London.,Local media pointed to the chants of “Bio must go” among protesters as they gathered in the capital, and the president accused some of the demonstrators of consisting of “APC Warriors,” a reference to the opposition All People’s Congress party, which governed the country from 2007 until 2018, when Bio’s Sierra Leone People’s Party won national elections.,No doubt mindful of the violent civil war which shook the country between 1991 and 2002, claiming as many as 70,000 lives and displacing over 2.5 million people, Bio vowed that “in the coming weeks and months, [the] government will undertake necessary security actions meant to guarantee the peace and security of all citizens.”,“The security forces will, and must, act with great restraint and within their professional codes of service. But be assured that my government will crack down hard on violent insurrectionists, their collaborators, their sponsors and their supporters. My government will relentlessly fight those who would rather use terror and gruesome violence to achieve political goals,” the president said.,As a government, we will continue our engagement with Civil Society as we strive to promote sustainable peace, national cohesion and socio-economic development in Sierra Leone. #newdirectionagenda— President Julius Maada Bio (@PresidentBio) August 18, 2022,Bio did not elaborate on who these “sponsors” and “supporters” were, or whether they included any foreign actors.,Geopolitical Context,Like other African nations, Sierra Leone recently rejected calls by Washington and Brussels to show solidarity with the West and Ukraine and impose sanctions on Russia. But even before the escalation of the Ukraine crisis, relations between Freetown and Washington were tense at times. Last year, US President Joe Biden snubbed Bio by refusing to invite the African leader to the US’ so-called “Democracy Summit.” No reasons were given. However, neighboring Liberia, which faced mass civil unrest of its own between 2019 and 2020, and whose officials have been sanctioned by the US over suspected corruption, did get an invite.,While Sierra Leone maintains economic and political ties with its former British colonial masters, and remains a member of the Commonwealth of Nations, Freetown has sought to expand its partnerships with other geopolitical power centers, including Russia and China. President Bio attended the Russia-Africa Summit in Sochi in 2019, where he discussed ways to strengthen economic cooperation between the distant nations. In February 2021, Freetown signed onto Moscow’s efforts to prevent the deployment of weapons in outer space. In May 2021, Bio spoke by phone to President Xi Jinping of China, where they discussed the friendly, “brotherly” relations between the two nations, as well Chinese assistance to Freetown in measures against COVID, and agricultural and economic development.,In this context, the reactions of major foreign powers to this month’s unrest have been telling. While the United States, Britain, and the European Union collectively expressed “grave concern” over the “disturbing reports of violence” and urged the parties to “stay calm, promote accountability and ensure respect for human rights,” China’s Embassy smoothed over the protests altogether, refraining from wagging its finger at Freetown and instead trumpeting the expanding cooperation between the two countries.,We are gravely concerned by reports of violence surrounding today’s demonstrations in Sierra Leone. We urge all parties to stay calm, promote accountability, and ensure respect for human rights and fundamental freedoms.— Bureau of African Affairs (@AsstSecStateAF) August 10, 2022,Similarly, while UK High Commissioner to Sierra Leone Lisa Chesney lectured President Bio about how “violence has no place in a democracy and the necessary investigation into August 10 can sit alongside de-escalation,” the Russian Embassy in the Republic of Guinea, which concurrently serves as the Embassy in Sierra Leone, only presented a bare bones report on the situation in the country, Bio’s meetings with community and tribal leaders, and indicated that an internal “debriefing” was being created “regarding the causes, course and consequences of the riots on August 10.”。所有形式的光--从无线电波到伽马射线--都可以被偏振。跟我们用来减少阳光从潮湿的道路或挡风玻璃上反弹的眩光的偏光太阳镜不同，IXPE的探测器绘制了进入的X射线光的轨迹。科学家们可以利用这些单独的轨迹记录来计算出偏振，这就说明了X射线所经历的故事。仙后座A（简称Cas A）是IXPE开始收集数据后观察到的第一个天体。仙后座A被选中的原因之一是它的冲击波--就像喷射器产生的音爆--是银河系中最快的一些。冲击波是由超新星爆炸产生，超新星爆炸摧毁了一颗巨大的恒星后，它坍塌了。

C | 爆炸产生的光线在三百多年前掠过地球。哈佛大学和史密森学会天体物理学中心的Pat Slane说道：“如果没有IXPE，我们一直在错过有关Cas A这样的天体的关键信息，他领导着IXPE对超新星遗迹的调查。这个结果让我们了解到这个爆炸恒星的碎片的一个基本方面--其磁场的行为。”磁场是不可见的，它对质子和电子等移动的带电粒子进行推拉。在家里，它们负责使磁铁粘在厨房的冰箱上。

D | 在极端条件下，如一颗爆炸的恒星，磁场可以将这些粒子提升到接近光速。尽管它们的速度超快，但被Cas A中的冲击波卷起的粒子并没有飞离超新星残骸，这是因为它们被冲击波后的磁场所困住。这些粒子被迫绕着磁场线旋转，电子发出一种强烈的光，称为“同步辐射”，它是偏振的。通过研究这种光的偏振，科学家可以在非常小的尺度上“反向设计”Cas A内部发生的事情--这些细节以其他方式很难或不可能观察到。偏振的角度告诉我们这些磁场的方向。如果靠近冲击前沿的磁场非常纠结，那么来自不同磁场方向的区域的混乱的混合辐射将发出较小的偏振量。以前用射电望远镜对Cas A的研究表明，射电同步辐射是在几乎整个超新星遗迹的区域产生。天文学家发现，只有少量的无线电波被极化--约5%。他们还确定，磁场的方向是径向的，就像车轮的辐条，从残余物的中心附近向边缘扩散。另一方面，来自NASA钱德拉X射线天文台的数据显示，X射线同步辐射主要来自沿冲击的稀薄区域，靠近残余物的圆形外缘，在那里磁场被预测为与冲击对齐。钱德拉和IXPE使用不同种类的探测器，具有不同的角度分辨率或清晰度。1999年发射的钱德拉的第一张科学图像也是Cas A的。相反，IXPE的数据显示，X射线中的磁场倾向于在径向方向上排列，甚至非常接近冲击前沿。X射线还显示出比无线电观测所显示的偏振量要低，这表明X射线来自于混合了许多不同磁场方向的湍流区。

E | 来自阿姆斯特丹大学的Jacco Vink博士是描述Cas A的IXPE结果的论文的第一作者，他说道：“这些IXPE结果跟我们的预期不同，但作为科学家，我们喜欢惊喜。事实上，较小比例的X射线是偏振的，这是Cas A的一个非常有趣的--而且以前没有发现的--特性。”关于Cas A的IXPE结果正在吊起人们的胃口，对目前正在进行的超新星残余物的更多观测。

F | 科学家们希望每一个新观测对象都能揭示新的答案--并提出更多的问题--关于这些为宇宙注入关键元素的重要天体。意大利国家天体物理研究所/罗马空间天体物理学和行星学研究所的Riccardo Ferrazzoli博士说道：“这项研究体现了IXPE给天体物理学带来的所有新东西。我们不仅首次获得了这些来源的X射线偏振特性的信息，而且我们还知道这些偏振特性在超新星的不同区域是如何变化的。作为IXPE观测活动的第一个目标，Cas A提供了一个天体物理学的‘实验室’来测试团队近年来开发的所有技术和分析工具。

G | ”研究论文共同作者、阿姆斯特丹大学的Dmitry Prokhorov表示：“这些结果为将电子加速到令人难以置信的高能量所需的环境提供了一个独特的视角。我们只是在这个侦探故事的开始，但到目前为止，IXPE的数据正在为我们提供新的线索来进行追踪。

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Published on:18:17:30