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تسجيل مستخدم جديدMinding the gap: GW190521 as a straddling binary
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Models for black hole (BH) formation from stellar evolution robustly predict the existence of a pair-instability supernova (PISN) mass gap in the range $sim50$ to $sim120$ solar masses. This theoretical prediction is supported by the binary black holes (BBHs) of LIGO/Virgos first two observing runs, whose component masses are well-fit by a power law with a maximum mass cutoff at $m_mathrm{max}=40.8^{+11.8}_{-4.4},M_odot$. Meanwhile, the BBH event GW190521 has a reported primary mass of $m_1=85^{+21}_{-14},M_odot$, firmly above the inferred $m_mathrm{max}$, and secondary mass $m_2=66^{+17}_{-18},M_odot$. Rather than concluding that both components of GW190521 belong to a new population of mass-gap BHs, we explore the conservative scenario in which GW190521s secondary mass belongs to the previously-observed population of BHs. We replace the default priors on $m_1$ and $m_2$, which assume that BH detector-frame masses are uniformly distributed, with this population-informed prior on $m_2$, finding $m_2<48,M_odot$ at 90% credibility. Moreover, because the total mass of the system is better constrained than the individual masses, the population prior on $m_2$ automatically increases the inferred $m_1$ to sit emph{above} the gap (39% for $m_1 > 120,M_odot$, or 25% probability for $m_1>130,M_odot$). As long as the prior odds for a double-mass-gap BBH are smaller than $sim 1:15$, it is more likely that GW190521 straddles the pair-instability gap. We argue that GW190521 may be the first example of a straddling binary black hole, composed of a conventional stellar mass BH and a BH from the ``far side of the PISN mass gap.
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The gravitational-wave signal GW190521 is consistent with a binary black hole merger source at redshift 0.8 with unusually high component masses, $85^{+21}_{-14},M_{odot}$ and $66^{+17}_{-18},M_{odot}$, compared to previously reported events, and sho
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