Merger of two الثقوب السوداء has three stages: inspiral, merger and ringdown phases. Characteristic موجات الجاذبية are emitted in each phase. The last ringdown phase is very brief and encode information about properties of final الثقب الأسود. Reanalysis of data from binary الثقب الأسود merger event GW190521 has provided, for the first time, evidence of signature aftershocks of the merger in the form of two separate faint ringdown frequencies produced by the resulting single الثقب الأسود as it settled down to a stable symmetrical form. This is the first detection of multiple gravitational-wave frequencies in the ringdown stage. Just like a bell ‘rings’ for some time after being stuck, the resulting single distorted الثقب الأسود formed after the merger ‘rings’ for some time emitting faint موجات الجاذبية before achieving symmetrical stable form. And, just the way shape of the bell determines the specific frequencies with which the bell rings, similarly, as per no-hair theorem, mass and spin of the الثقب الأسود determine ringdown frequencies. Hence, this development paves the way for use of ringdown frequencies to study properties of final الثقب الأسود.
الثقوب السوداء are massive objects with extremely strong gravitational fields. When two تدور حول الثقوب السوداء spiral around each other and eventually coalesce, the fabric of الفضاء-times around them are disturbed that creates ripples of موجات الجاذبية radiating outwards. Since September 2015 when gravitational-wave astronomy began with LIGO’s first detection of موجات الجاذبية generated by merger of two الثقوب السوداء 1.3 billion light years away, merging الثقوب السوداء are now routinely detected almost once every week.
اندماج الثقوب السوداء has three phases. When the two الثقوب السوداء are widely separated, they slowly فلك each other emitting weak موجات الجاذبية. The binary gradually moves to smaller and smaller مدارات as the energy of the system is lost in the form of موجات الجاذبية. وهذا هو المرحلة الملهمة من الاندماج. التالي هو مرحلة الاندماج عندما يكون الاثنان الثقوب السوداء get close enough to coalesce to form a single الثقب الأسود with distorted shape. Strongest gravitational waves (GWs) are emitted at this stage which are now routinely detected and recorded by gravitational-wave observatories.
تتبع مرحلة الاندماج مرحلة قصيرة جدًا تسمى مرحلة النغمة wherein the resulting single distorted الثقب الأسود quickly achieves more stable spherical or spheroidal form. موجات الجاذبية emitted in the ringdown phase are damped and much fainter than the GWs released in the merger phase. Just as a bell ‘rings’ for some time after being stuck, the resulting single الثقب الأسود ‘rings’ for some time emitting much fainter موجات الجاذبية before achieving symmetrical stable form.
The faint multiple ringdown frequencies of موجات الجاذبية released during the ringdown phase of merger of two الثقوب السوداء were undetected so far.
A research team has recently been successful in detecting multiple gravitational-wave frequencies in the ringdown stage of binary الثقب الأسود merger event GW190521. They searched for individual fading tones in the ringdown frequencies without considering any relation with frequencies and damping times and were successful in identifying two modes implying the resulting deformed الثقب الأسود emitted at least two frequencies after the merger. This was predicted by Einstein’s general relativity hence the result confirms the theory. Further, researchers compared the frequencies and damping times of the two ringdown modes found in the merger event to test the “no-hair theorem” (that الثقوب السوداء are completely characterised by mass and spin and no other “hair” is needed to describe its features) and found nothing beyond general relativity.
يعد هذا علامة فارقة لأنه كان يُعتقد على نطاق واسع أن مراقبة ترددات الرنين المتعددة لن تكون ممكنة قبل أن يصبح الجيل التالي من كاشفات موجات الجاذبية متاحًا في المستقبل.
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مصادر:
- كابانو، سي دي وآخرون. 2023. طيف شبه طبيعي متعدد الأوضاع من ثقب أسود مضطرب. رسائل المراجعة البدنية. المجلد. 131، العدد 22. 1 ديسمبر 2023. DOI: https://doi.org/10.1103/PhysRevLett.131.221402
- معهد ماكس بلانك لفيزياء الجاذبية (معهد ألبرت أينشتاين)، 2023. الأخبار – لمن يرن الثقب الأسود. متواجد في https://www.aei.mpg.de/749477/for-whom-the-black-hole-rings?c=26160
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