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Hidden supermassive black holes brought to life by galaxies on collision course
Astronomers have found that supermassive black holes obscured by dust are more likely to grow and release tremendous amounts of energy when they are inside galaxies that are expected to collide with a neighboring galaxy. The new work, led by researchers from Newcastle University, is published in Monthly Notices of the Royal Astronomical Society.
Galaxies, including our own Milky Way, contain supermassive black holes at their centers. They have masses equivalent to millions, or even billions, times that of our Sun. These black holes grow by 'eating' gas that falls on to them. However, what drives the gas close enough to the black holes for this to happen is an ongoing mystery.
One possibility is that when galaxies are close enough together, they are likely to be gravitationally pulled towards each other and 'merge' into one larger galaxy.
In the final stages of its journey into a black hole, gas lights up and produces a huge amount of energy. This energy is typically detected using visible light or X-rays. However, the astronomers conducting this study were only able to detect the growing black holes using infrared light. The team made use of data from many different telescopes, including the Hubble Space Telescope and infrared Spitzer Space Telescope.
The researchers developed a new technique to determine how likely it is that two galaxies are very close together and are expected to collide in the future. They applied this new method to hundreds of thousands of galaxies in the distant universe (looking at galaxies formed 2 to 6 billion years after the Big Bang) in an attempt to better understand the so-called 'cosmic noon', a time when most of the Universe's galaxy and black hole growth is expected to have taken place.
Understanding how black holes grew during this time is fundamental in modern day galactic research, especially as it may give us an insight into the supermassive black hole situated inside the Milky Way, and how our galaxy evolved over time.
As they are so far away, only a small number of cosmic noon galaxies meet the required criteria to get precise measurements of their distances. This makes it very difficult to know with high precision if any two galaxies are very close to each other.
This study presents a new statistical method to overcome the previous limitations of measuring accurate distances of galaxies and supermassive black holes at cosmic noon. It applies a statistical approach to determine galaxy distances using images at different wavelengths and removes the need for spectroscopic distance measurements for individual galaxies.
Data arriving from the James Webb Space Telescope over the coming years is expected to revolutionize studies in the infrared and reveal even more secrets about how these dusty black holes grow.
Sean Dougherty, postgraduate student at Newcastle University and lead author of the paper, says, "Our novel approach looks at hundreds of thousands of distant galaxies with a statistical approach and asks how likely any two galaxies are to be close together and so likely to be on a collision course."
Dr. Chris Harrison, co-author of the study, "These supermassive black holes are very challenging to find because the X-ray light, which astronomers have typically used to find these growing black holes, is blocked, and not detected by our telescopes. But these same black holes can be found using infrared light, which is produced by the hot dust surrounding them."
He adds, "The difficulty in finding these black holes and in establishing precise distance measurements explains why this result has previously been challenging to pin down these distant 'cosmic noon' galaxies. With JWST we are expecting to find many more of these hidden growing black holes. JWST will be far better at finding them, therefore we will have many more to study, including ones that are the most difficult to find. From there, we can do more to understand the dust that surrounds them, and find out how many are hidden in distant galaxies."
注释：
supermassive: adj
表示" [天]特大质量的"，如：To understand the first light of the universe, we really have to include the role of these supermassive black holes in galaxy formation.为了了解宇宙的第一个光线，我们真的要把特大质量的黑洞在星系形成过程中所承担的角色考虑进来。
cosmic： adj
表示" 宇宙的；"，如：I have mystical visions and cosmic vibrations. 我有神秘的幻觉和宇宙的震波。
galactic: adj
表示" 星系的；"，means "of or relating to a galaxy"，如：The Milky Way is a galactic system made up of many fixed stars. 银河系是由无数颗恒星组成的星际体系。
spectroscopic: adj
表示" 分光镜的"，means "of or relating to or involving spectroscopy"，如：The spectroscopic data muddy the picture further. 分光观测资料进一步扰乱了这一图景。
pin: v
表示"钉住；别住；固定住"，means " fasten or join with a pin or pins"，如：The general pinned the medal on the soldier's chest. 将军把奖章别在这位士兵的胸前。
中文简要说明：
天文学家发现，每个星系中心那个被尘埃遮蔽的超大质量黑洞，在与邻近星系（Galaxy）相撞的星系内更有可能成长并释放出巨大的能量，透过这一个现象和新的太空望远镜，天文学家终于有机会可以窥探星系中藏在尘埃后面的超大质量黑洞。这项新研究由纽卡斯尔大学（Newcastle University）的研究人员带领，目前发表在《皇家天文学会月刊》（Royal Astronomical Society）上。
据专业的科学研究新闻信息网站phys.org 报导，包括我们的银河系（Milky Way）在内的星系，它们的中心都有一个超大质量黑洞。这些黑洞的质量相当于我们太阳的数百万甚至数十亿倍。这些黑洞通过吞噬落入它们之中的气体来成长。
然而，将气体推至足够靠近黑洞的原因仍然是一个悬而未解的谜。还有一种可能性是，当星系彼此足够接近时，它们有可能因为引力相互拉近并合并成一个更大的星系。
在进入黑洞的最后阶段，这些气体会开始燃烧并产生巨大的能量。这种能量通常使用可见光或X射线来检测。然而，进行这项研究的天文学家们只能使用红外光来检测正在成长的黑洞。该团队利用了多个不同的望远镜的数据，包括哈伯太空望远镜（HST）和红外史匹哲太空望远镜（SST）。
未来几年，来自韦伯太空望远镜（JWST）的数据预计将彻底改变红外线研究，并揭示更多有关这些充满尘埃的超大质量黑洞成长的秘密。
他补充说：「在寻找这些黑洞并确定精确距离测量方面的困难解释了为什么以前很难确定这些遥远的『宇宙正午』星系（Cosmic Noon）。透过韦伯太空望远镜，我们预计将找到更多这些隐藏的成长黑洞。其中包括最难找到的黑洞。从那里，我们可以更多地了解包围它们的尘埃，并找出有多少个隐藏在遥远星系中。」
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