Merger of two svarthol has three stages: inspiral, merger and ringdown phases. Characteristic þyngdarbylgjur are emitted in each phase. The last ringdown phase is very brief and encode information about properties of final svarthol. Reanalysis of data from binary svarthol 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 svarthol 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 svarthol formed after the merger ‘rings’ for some time emitting faint þyngdarbylgjur 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 svarthol determine ringdown frequencies. Hence, this development paves the way for use of ringdown frequencies to study properties of final svarthol.
Svarthol are massive objects with extremely strong gravitational fields. When two bylgja svarthol spiral around each other and eventually coalesce, the fabric of pláss-times around them are disturbed that creates ripples of þyngdarbylgjur radiating outwards. Since September 2015 when gravitational-wave astronomy began with LIGO’s first detection of þyngdarbylgjur generated by merger of two svarthol 1.3 billion light years away, merging svarthol are now routinely detected almost once every week.
Sameiningin af svarthol has three phases. When the two svarthol are widely separated, they slowly sporbraut each other emitting weak gravitational waves. The binary gradually moves to smaller and smaller brautir as the energy of the system is lost in the form of þyngdarbylgjur. Þetta er innblástursfasi af samruna. Næsta er samruna áfanga þegar tveir svarthol get close enough to coalesce to form a single svarthol with distorted shape. Strongest gravitational waves (GWs) are emitted at this stage which are now routinely detected and recorded by gravitational-wave observatories.
Sameiningaráfanganum er fylgt eftir af mjög stuttum áfanga sem kallast hringingarstig wherein the resulting single distorted svarthol quickly achieves more stable spherical or spheroidal form. Þyngdarbylgjur 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 svarthol ‘rings’ for some time emitting much fainter þyngdarbylgjur before achieving symmetrical stable form.
The faint multiple ringdown frequencies of þyngdarbylgjur released during the ringdown phase of merger of two svarthol were undetected so far.
A research team has recently been successful in detecting multiple gravitational-wave frequencies in the ringdown stage of binary svarthol 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 svarthol 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 svarthol are completely characterised by mass and spin and no other “hair” is needed to describe its features) and found nothing beyond general relativity.
Þetta er áfangi vegna þess að almennt var talið að athuganir á mörgum hringingartíðni yrðu ekki mögulegar áður en næstu kynslóð þyngdarbylgjuskynjarar verða fáanlegir í framtíðinni.
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Heimildir:
- Capano, geisladiskur et al. 2023. Multimode Quasinormal Spectrum frá truflaðu svartholi. Líkamleg endurskoðunarbréf. Vol. 131, tbl. 22. 1. desember 2023. DOI: https://doi.org/10.1103/PhysRevLett.131.221402
- Max-Planck-Institut fürGravitationsphysik(Albert-Einstein-Institut), 2023. Fréttir – Fyrir hvern hringir svartholið. Fæst kl https://www.aei.mpg.de/749477/for-whom-the-black-hole-rings?c=26160
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