Merger of two черни дупки has three stages: inspiral, merger and ringdown phases. Characteristic гравитационни вълни are emitted in each phase. The last ringdown phase is very brief and encode information about properties of final черна дупка. Reanalysis of data from binary черна дупка 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 черна дупка 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 черна дупка formed after the merger ‘rings’ for some time emitting faint гравитационни вълни 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 черна дупка determine ringdown frequencies. Hence, this development paves the way for use of ringdown frequencies to study properties of final черна дупка.
Черни дупки are massive objects with extremely strong gravitational fields. When two орбита черни дупки spiral around each other and eventually coalesce, the fabric of пространство-times around them are disturbed that creates ripples of гравитационни вълни radiating outwards. Since September 2015 when gravitational-wave astronomy began with LIGO’s first detection of гравитационни вълни generated by merger of two черни дупки 1.3 billion light years away, merging черни дупки are now routinely detected almost once every week.
Сливането на черни дупки has three phases. When the two черни дупки are widely separated, they slowly орбита each other emitting weak гравитационни вълни. The binary gradually moves to smaller and smaller орбити as the energy of the system is lost in the form of гравитационни вълни. Това е вдъхновяваща фаза на коалесценция. Следващото е фаза на сливане когато двамата черни дупки get close enough to coalesce to form a single черна дупка with distorted shape. Strongest gravitational waves (GWs) are emitted at this stage which are now routinely detected and recorded by gravitational-wave observatories.
Фазата на сливане е последвана от много кратък етап, наречен ringdown етап wherein the resulting single distorted черна дупка quickly achieves more stable spherical or spheroidal form. Гравитационни вълни 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 черна дупка ‘rings’ for some time emitting much fainter гравитационни вълни before achieving symmetrical stable form.
The faint multiple ringdown frequencies of гравитационни вълни released during the ringdown phase of merger of two черни дупки were undetected so far.
A research team has recently been successful in detecting multiple gravitational-wave frequencies in the ringdown stage of binary черна дупка 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 черна дупка 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 черни дупки are completely characterised by mass and spin and no other “hair” is needed to describe its features) and found nothing beyond general relativity.
Това е крайъгълен камък, тъй като се смяташе, че наблюдението на множество честоти на звънене няма да е възможно преди следващото поколение детектори за гравитационни вълни да станат налични в бъдеще.
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Източници:
- Капано, CD и др. 2023. Многомодов квазинормален спектър от смутена черна дупка. Писма за физически преглед. Vol. 131, брой 22. 1 декември 2023 г. DOI: https://doi.org/10.1103/PhysRevLett.131.221402
- Max-Planck-Institut fürGravitationsphysik (Albert-Einstein-Institut), 2023 г. Новини – За кого звъни черната дупка. Наличен в https://www.aei.mpg.de/749477/for-whom-the-black-hole-rings?c=26160
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