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posted by janrinok on Monday January 13 2020, @09:17PM   Printer-friendly
from the black-hole-sun dept.

A stripped helium star solves the massive black hole mystery:

The putative black hole was detected indirectly from the motion of a bright companion star, orbiting an invisible compact object over a period of about 80 days. From new observations, a Belgian team showed that the original measurements were misinterpreted and that the mass of the black hole is, in fact, very uncertain. The most important question, namely how the observed binary system was created, remains unanswered. A crucial aspect is the mass of the visible companion, the hot star LS V+22 25. The more massive this star is, the more massive the black hole has to be to induce the observed motion of the bright star. The latter was considered to be a normal star, eight times more massive than the Sun.

A team of astronomers from Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) and the University of Potsdam had a closer look at the archival spectrum of LS V+22 25, taken by the Keck telescope at Mauna Kea, Hawaii. In particular, they were interested in studying the abundances of the chemical elements on the stellar surface. Interestingly, they detected deviations in the abundances of helium, carbon, nitrogen, and oxygen compared to the standard composition of a young massive star. The observed pattern on the surface showed ashes resulting from the nuclear fusion of hydrogen, a process that only happens deep in the core of young stars and would not be expected to be detected at its surface.

[...] The authors concluded that LS V+22 25 must have interacted with its compact companion in the past. During this episode of mass-transfer, the outer layers of the star were removed and now the stripped helium core is visible, enriched with the ashes from the burning of hydrogen.

Journal Reference:

A. Irrgang, S. Geier, S. Kreuzer, I. Pelisoli, U. Heber. A stripped helium star in the potential black hole binary LB-1. Astronomy & Astrophysics, 2020; 633: L5 DOI: 10.1051/0004-6361/201937343


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  • (Score: 2) by HiThere on Tuesday January 14 2020, @01:23AM

    by HiThere (866) Subscriber Badge on Tuesday January 14 2020, @01:23AM (#942936) Journal

    Well....but if it was stripped of its surface layers, then it might not have been well aged. After all, hydrogen burning starts pretty young in a star's life cycle. Usually we can't see the interior, so maybe this is what's normally there.

    It's my guess that we'd need a bunch of similar stars to compare against, but it's going to be hard to find stars without their outer layers stripped off were we can see the inner layers. And any we can find will be, let's just say, unusual.

    Usually when a star is stripped of it's outer layers it's because the star has swollen in the "red giant" stage, but black holes can plausibly consume more voraciously. (The orbits could be pretty important in deciding this. How close do they come, and how much could the companion have eaten.)

    OTOH, unless there were originally three stars, one of which got ejected, the black hole should have lost a lot of mass during it's collapse, and so the binary orbit should have widened. And black holes aren't any more powerfully attractive at a given distance than other stars, though they do concentrate their mass, so if you would have been below the surface of the parent star, the black hole residuum might well pull more powerfully.

    Basically, "I dunno". If it started out at a ternary system then maybe the "stripped" star *was* pretty young. If it started out as a binary, then it probably went into "red giant" expansion. But that's just a guess.

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