An ultraviolet-optical flare from the tidal disruption of a helium-rich stellar core

摘要

The flare of radiation from the tidal disruption and accretion of a star can be used as a marker for supermassive black holes that otherwise lie dormant and undetected in the centres of distant galaxies. Previous candidate flares have had declining light curves in good agreement with expectations, but with poor constraints on the time of disruption and the type of star disrupted, because the rising emission was not observed. Recently, two 'relativistic' candidate tidal disruption events were discovered, each of whose extreme X-ray luminosity and synchrotron radio emission were interpreted as the onset of emission from a relativistic jet. Here we report a luminous ultraviolet-optical flare from the nuclear region of an inactive galaxy at a redshift of 0.1696. The observed continuum is cooler than expected for a simple accreting debris disk, but the well-sampled rise and decay of the light curve follow the predicted mass accretion rate and can be modelled to determine the time of disruption to an accuracy of two days. The black hole has a mass of about two million solar masses, modulo a factor dependent on the mass and radius of the star disrupted. On the basis of the spectroscopic signature of ionized helium from the unbound debris, we determine that the disrupted star was a helium-rich stellar core.%遥远星系中的中央超大质量黑洞我们通常是看不见的，但有时它们的存在会以被吸积到黑洞中的一颗恒星的潮汐式扰动所产生的耀斑的形式而显现出来。这样的事件是罕见的，经常我们只能看到这种事件的后期阶段，但这里Gezari等人报告了对来自位于红移值为0．1 696的 个非活动星系的”核区域”的一个紫外线rn和可见光耀斑所做的详细监测——该耀斑首次在2010年5月31日被看到，7月份达到峰值水平，9月份结束。所观察到的连续体要比一个简单的、吸积中的碎片盘所预期的温度低，但采样很好的光曲线升降却与所预测的质量一吸积率一致。该黑洞约有200万个太阳质量，被扰动的恒星有一个富含氦的恒星核心——这是本文作者根据来自未束缚碎片的离子化氦的光谱特征推导出的。