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Messy eating habits might reveal elusive black hole
Black holes have a reputation for snacking on stars, but some of these celestial garbage disposals may be messier than others, according to new research.
Astrophysicists used 3D computer models to show that intermediate-mass black holes take a few bites out of wayward stars before tossing away the stellar crumbs and leaving a cosmic trail.
Researchers made the discovery while running simulations on black holes of various masses and sending sun-size stars past them. The clues uncovered in the experiment might help astronomers find intermediate-mass black holes by searching for evidence of their behaviors.
During the simulations, the intermediate-mass black hole snagged the star in its orbit, and each time the star made another lap, the black hole took another bite out of it. When only the dense, misshapen core of the star was left, the black hole discarded it and sent it flying across the galaxy.
A study describing the modeling analysis has been accepted for publication in The Astrophysical Journal, and the findings will be presented Tuesday at the American Physical Society’s April meeting.
“We obviously cannot observe black holes directly because they don’t emit light,” said lead study author Fulya Kıroğlu, a doctoral student of astrophysics at Northwestern University’s Weinberg College of Arts and Sciences in Evanston, Illinois, in a statement. She is also a member of the university’s Center for Interdisciplinary Exploration and Research in Astrophysics.
“So, instead, we have to look at the interactions between black holes and their environments. We found that stars undergo multiple passages before being ejected. After each passage, they lose more mass, causing a flair of light as (it’s) ripped apart. Each flare is brighter than the last, creating a signature that might help astronomers find them.”
The search for elusive black holes
Astrophysicists are still trying to prove if intermediate-mass black holes exist in the first place. The elusive celestial objects, estimated to be between three and 10 times the mass of our sun, are created when exploding stars collapse.
The mass of a medium-mass black hole is thought to be between that of a supermassive black hole and a much lower-mass black hole. A supermassive black hole is found at the center of most large galaxies and can be millions to billions of times the mass of our sun.
“Their presence is still debated,” said Kıroğlu. “Astrophysicists have uncovered evidence that they exist, but that evidence can often be explained by other mechanisms. For example, what appears to be an intermediate-mass black hole might actually be the accumulation of stellar-mass black holes.”
During the 3D modeling experiment, stars were able to complete as many as five orbits around an intermediate-mass black hole before being kicked away. With each pass, the star lost more mass while being slowly ripped apart. The remnants were ejected at blinding speed back into the galaxy — enough to create a bright light pattern that astronomers could watch for in their quest to prove the existence of the invisible medium-mass black holes.
“It’s amazing that the star isn’t fully ripped apart,” Kıroğlu said. “Some stars might get lucky and survive the event. The ejection speed is so high that these stars could be identified as hyper-velocity stars, which have been observed at the centers of galaxies.”
注释：
elusive: adj
表示"难懂的；难捉摸的"，means "difficult to detect or grasp by the mind or analyze"，如：Number is a crucial but elusive concept in English teaching and learning. 数是英语教学中的一个关键而又难以捉摸的概念。
celestial: adj
表示"天上的；非凡的"，means "of or relating to the sky"，如：The rosy light yet beamed like a celestial dawn. 玫瑰色的红光依然像天上的朝霞一样绚丽。
Astrophysicist: n
表示"天体物理学家"，means "an astronomer who studies the physical properties of celestial bodies"，如：When I grew up, I became a professional astrophysicist. 长大之后，我成了一名职业的天体物理学家。
snag: v
表示" 划破；碰到（暗礁或枯树上）；清除（暗礁等）"，means "catch on a snag;hew jaggedly"，如：Her tights were badly snagged. 她的裤袜划破了一大片。The river has to be snagged. 必须清除这条河的暗桩。
remnant: n
表示" 残余"，means " a part that remains"，如：I will sell this remnant to you, at cost. 我愿将此剩货照成本卖给你。
中文简要说明：
国外科学家利用计算机仿真黑洞吞噬恒星的过程，发现黑洞吃相可能就像「小孩般」大快朵颐，暴吃一顿后留下剩余「碎屑」不吃，然后乱撒一地。
综合国外有线电视新闻网（CNN）、福斯新闻（Fox News）报道，国外西北大学温伯格文理学院（Weinberg College of Arts and Sciences）博士生姬萝芦（Fulya Kiroglu）率领团队，利用3D计算机模型仿真太阳般大小的恒星遇上不同质量黑洞的过程。
姬萝芦说，当恒星靠近「中等质量黑洞」（intermediate-mass black hole）时，会被困在黑洞的轨道上运行，接着黑洞就会开始暴力且漫长地享用大餐，恒星每运行一圈，黑洞就会咬一口，恒星就这样慢慢在被撕裂的过程中失去质量。她说恒星最多能完成5次绕行，最终只剩下密度相当大且奇形怪状的核心，接着黑洞就会丢弃这些「恒星碎屑」，将它们甩飞回星系，这些碎屑被弹飞的速度快到足以留下亮光，而这些亮光是天文学家能观测到的。
根据西北大学公开的模拟画面，恒星被吸进黑洞时撞击出绚烂光彩，恒星仍持续绕行黑洞，每被吞噬一次就散发出一道螺旋亮光。福斯新闻描述黑洞的吃相就像「幼童」在吃周日的早午餐。
姬萝芦等人的研究目前已获国际期刊《天文物理期刊》（Astrophysical Journal）授权发表。 姬萝芦说，由于黑洞不会散发光线，因此科学家无法直接观测黑洞，这时候就需要观察黑洞与环境之间的互动，而模型中出现的亮光可能就是黑洞存在的线索，她说：「我们发现恒星被弹射前会绕行多次，每次运行都会失去一些质量，被撕裂时会散发一束光，每一束光比前一次还要亮…。」这些光亮有助于科学家发现它们的存在。
她说科学家现在仍试着证明中等质量黑洞是否存在，过去科学家确实提出过证据佐证，但最终这些证据总能用来解释成其他机制。不过如果中等质量黑洞确实存在，运行方式可能就会像他们模拟的成果。 中等质量黑洞的质量大约是太阳质量的3至10倍。
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