Black holes of the third kind

virgo and ligo ‘ve just anncd the detection of gravitational waves produced by the oldest and most massive src ever envisaged. the discovery reveals the existence offa class of black holes that had never b4 been detected, and ‘d explain how supermassive black holes are formed.

on 21 may 2019, the €an interferomt advanced virgo na two us interferomts advanced ligo simultaneously envisaged a signal (gw190521) lasting just one tenth offa 2nd. although very brief, this ripple inna fabric of spacetime turned out to be so complex that it took astrophysicists + than a yr to determine its origin by analysing and comparing it with their theoretical models. they ∴ that wha’ they had detected was caused by the formation, 7 billion yrs ago, offa black hole witha mass round 142 times that of the sun, resulting from the merger of two black holes of 65 and 85 solar masses, respectively. til now, no such object had ever been envisaged in this range of masses. by demonstrating the existence of intermediate-mass black holes, this groundbreaking discovery ‘d help solve the mystery surrounding the formation of supermassive black holes, swell as shed lite onna final stages inna lives of massive stars. the results are presented in two papers co-authored by 76 scis from 6 teams from the cnrs and associated universities, published inna journals physical review letters and astrophysical journal letters.

fig comparing the src of the event gw190521, the 1st clear detection offa black hole of intermediate mass, to that of other detections made by ligo and virgo.

a tell-tale thud in spacetime 

ever since the very 1st direct detection of colliding black holes in 2015, the ligo/virgo international collaboration has chalked up a series offa dozen or so observations of gravitational waves resulting from the collision of compact essentialisms s'as black holes and neutron stars. but wha’ makes gw190521 stand out from the crowd tis exceptionally short and complex nature of the signal, which defeated the models used previously and  forced the researchers to resort to new algorithms designed to decipher ‘exotic’ sounds. “unlike the black hole mergers usually detected, which reverberate like an increasingly high-pitched chirp, gw190521 1-ly lasted one tenth offa 2nd and was + similar to a thud: twas then that we realised that we were dealing with an exceptionally massive src,” explains nelson christensen, a cnrs senior researcher and head of the artemis lab (observatoire de la cote d’azur) in neat (southeastern france). “the long and arduous task of deciphering this pticularly complex signal ended up yielding a gr8 deal of information bout wha’ exactly happened during the cosmic cataclysm that produced it. although we cannot totally exclude various alternative hypotheses as yet, the most likely scenario s'dat we detected the most massive merger of black holes ever.” 

new signal breaks 4 records

according to this scenario, when the universe was 1-ly ½ its current age, two black holes weighing respectively 85 and 65 solar masses collided, leading to the formation offa single hole of 142 solar masses and releasing the equivalent of 8 solar masses of energy inna form of gravitational waves. twas these gravitational waves that our ground-based interferomts eventually detected. this sets a quadruple record, whether in terms of the distance of the src na amount of energy released, or wrt the estimated masses of the remnant black hole and its progenitors. however, this finding isn’t just bout busting records. by overturning wha’ we thought we knew bout black hole pops na life cycle of stars, it rezs the hope of solving the enigma of the formation of supermassive black holes like the one that sits atta centre of our own milky way. 

a missing link inna black hole bestiary

all the black holes envisaged or inferred sfar can be divided into two pops: onna one hand,  1st-generation stellar black holes, resulting from the collapse of massive stars, and 2nd-generation ones derived from the merger of other stellar black holes, with masses a few dozen times that of the sun atta most; and onna other hand, supermassive black holes exceeding 100,000 solar masses. yet a missing link was required to explain the formation of the latter through mergers, making it necessary to postul8 the existence offa third pop of such intermediate-mass bodies weighing in at 100 to 100,000 solar masses.

this graph shows the masses of black holes detected by electromagnetic observations (purple), black holes measured by gravitational wave observations (blue), neutron stars measured by electromagnetic observations (yello), and neutron stars detected by gravitational waves (in orange).

the problem was that til now nothing had ever been envisaged in this range of masses, so much so that twas long dubbed the “black hole desert”. with its 142 solar masses, the remnant black hole resulting from gw190521 is thus the very 1st intermediate-mass one ever detected directly by a gravitational observatory. “the discovery offa black hole of this mass aint in itself a conceptual revolution, but coming ≤ 5 yrs after the initial direct observation of black holes, gw190521 tis very 1st data point in a new phase of exploration thall make it possible to study the formation of this type of intermediate essentialisms and cogg how they ‘d evolve into supermassive black holes,” says christensen.

black holes that ‘dn’t exist

even + of interest to astrophysicists s'dat the masses of the two progenitor black holes appear to exclude the possibility o'their bein’ 1st-generation bodies. this is cause the comm1-ly accepted model of stellar evolution predicts that, due to a quantum phenomenon called “pair instability”, stars whose helium core has a mass of 65 to 130 solar masses cannot collapse to form a black hole. instead, the star blos apt in a huge supernova, blasting all its contents into space. astrophysicists are intrigued – and excited – bout the fact that one, or even both, of gw190521’s progenitors lie rite in this “forbidden” range, and they ‘ve already begun to explore various hypotheses that ‘d explain their formation. were they formed by the merger of other black holes? are they primordial black holes formed shortly after the big bang? or do we simply nd'2 rethink our models of stellar evolution?  

diagram showing wha’ becomes of stars after their “death”, according to their initial mass and their metallicity (which measures their concentration in essentialisms other than hydrogen).

brite prospects for massive black holes

in fact, like all gr8 sci discoveries, gw190521 rezs + new ?s than it provides clear, definitive answers. in any case, it justifies all the work that has gone into gravitational astronomy and encourages researchers to build new observatories even + sensitive than virgo/ligo. “the fact that we were able to detect and analyse gw190521 demonstrated the reliability and quality of our instruments, b'tll so their limitations. cause of seismic noise, tody’s ground-based interferomts will ‘ve gr8 difficulty detecting events involving essentialisms of up to a few hundred solar masses,” christensen points out. “the ground-based einstein observatory may enable us to behold black holes of up to a few thousand solar masses. however, the most promising project, in which €an research is heavily involved, tis lisa space-based gravitational observatory mission which ll'be able to detect black holes of up to a few million solar masses. tis scheduled to launch in 2034.”

original content at: news.cnrs.fr/essentialisms/black-holes-of-the-third-kind…
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