Black holes may merge with light of a tril­lion suns, sci­en­tists say

Iran Daily - - Science & Technology -

When black holes col­lide, the en­su­ing cos­mic drama was as­sumed to play out un­der the cloak of dark­ness, given that both ob­jects are in­vis­i­ble. But now as­tronomers be­lieve they have made the first op­ti­cal ob­ser­va­tions of such a merger, marked by a blaze of light a tril­lion times brighter than the Sun.

The flare was linked to a known black hole merger de­tected last year by the Laser In­ter­fer­om­e­ter Grav­i­ta­tional-wave Ob­ser­va­tory (LIGO) which picked up ripples sent out through the fabric of space. The lat­est ob­ser­va­tions sug­gest that when these cat­a­clysmic events oc­cur within the ac­cre­tion disk of an even more gi­gan­tic black hole, they are bril­liantly il­lu­mi­nated by the sur­round­ing dust and gas, mak­ing them also vis­i­ble to op­ti­cal tele­scopes, the Guardian re­ported.

“This su­per­mas­sive black hole was bur­bling along for years be­fore this more abrupt flare,” said Matthew Gra­ham, a re­search pro­fes­sor of as­tron­omy at the Cal­i­for­nia In­sti­tute of Tech­nol­ogy and lead author of the work. “We con­clude that the flare is likely the re­sult of a black hole merger.”

The au­thors have not en­tirely ruled out other sources, but Saavik Ford, a coau­thor based at the City Univer­sity of New York, said the win­dow of doubt was nar­row. “We are 99.9 per­cent sure,” she said.

Pro­fes­sor Al­berto Vec­chio, the di­rec­tor of the In­sti­tute of Grav­i­ta­tional Wave As­tron­omy at the Univer­sity of Birm­ing­ham, said ex­perts would now be watch­ing closely to see how the lat­est ob­ser­va­tions align with a de­tailed anal­y­sis of the same event due to be pub­lished in the com­ing months by LIGO sci­en­tists. “If the two in­de­pen­dent ob­ser­va­tions line up … this would re­ally be some­thing rather spec­tac­u­lar,” he said.

The ob­ser­va­tions came af­ter Ford and her col­league, Barry Mcker­nan, made the­o­ret­i­cal pre­dic­tions that black hole merg­ers would be vis­i­ble, con­trary to ex­pec­ta­tions, if they oc­curred against the back­drop of the ac­cre­tion disk of a third su­per­mas­sive black hole.

Ford and Mcker­nan teamed up with Gra­ham, a project sci­en­tist for the Zwicky Tran­sient Fa­cil­ity (ZTF), an all­sky sur­vey tele­scope de­signed to spot bright events. “It turns out to be per­fect for some­thing like this,” said Ford.

The sci­en­tists trawled through the Zwicky data look­ing for any flares that co­in­cided in place and time with known col­li­sions that had been de­tected by LIGO, which re­leases pub­lic alerts each time a de­tec­tion is made. One event stood out: A merger re­ferred to as S190521g that LIGO de­tected in May last year.

“It’s cer­tainly not one of the things you would have pre­dicted three years ago when we started the sur­vey,” said Gra­ham.

Closer anal­y­sis sug­gested the merger had taken place in the vicin­ity of a dis­tant su­per­mas­sive black hole called J1249+3449, with a di­am­e­ter equiv­a­lent to Earth’s or­bit around the Sun. The pair of smaller black holes sat at the outer reaches of the ac­cre­tion disk, a halo of stars, dust and gas swirling around the vast cen­tral sink­hole. “These ob­jects swarm like an­gry bees around the mon­strous queen bee at the cen­ter,” said Ford.

As the pair of black holes, each around the size of the Isle of Wight in the UK and with a com­bined mass of 150 suns, spi­ral in­wards and co­a­lesce, grav­i­ta­tional waves are sent out across space and the new, merged ob­ject ex­pe­ri­ences a kick in the op­po­site di­rec­tion, send­ing it plough­ing through the dust and gas of the disk and out into sur­round­ing space.

“It’s the re­ac­tion of the gas to this speed­ing bul­let that cre­ates a bright flare, vis­i­ble with tele­scopes,” said Mcker­nan.

Read the full ar­ti­cle on: www.irandai­ly­on­line.ir/news/270626. html

R. HURT (IPAC)/CAL­TECH An artist’s im­pres­sion of a su­per­mas­sive black hole and its sur­round­ing disk of gas with two smaller black holes em­bed­ded in it

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