HR 6819 - das bislang nächste Schwarze Loch

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Im dreifachen Sternsystem HR 6819 wurde mit Echelle-Messungen von der ESO ein stellares Schwarzes Loch identifiziert. Mit einer visuellen Helligkeit von 5.36 mag bei einem Abstand von 1010 Lj ist es das nächste und bislang einzige mit bloßem Auge sichtbare Sternsystem (allerdings am Südsternhimmel) mit einem stellaren Schwarzen Loch:

A naked-eye triple system with a nonaccreting black hole in the inner binary

ESO Instrument Finds Closest Black Hole to Earth

A team of astronomers from the European Southern Observatory (ESO) and other institutes has discovered a black hole lying just 1000 light-years from Earth. The black hole is closer to our Solar System than any other found to date and forms part of a triple system that can be seen with the naked eye. The team found evidence for the invisible object by tracking its two companion stars using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. They say this system could just be the tip of the iceberg, as many more similar black holes could be found in the future.
 
In einem Artikel bei S&T werden allerdings Zweifel genannt:

Closest Black Hole To Earth? Maybe

However, Hugues Sana (KU Leuven, Belgium) expresses misgivings. The team didn’t include their disentangling analysis in the paper (it’ll be published later). Although Sana agrees there are clearly two stars in the system - the Be star with wide spectral lines, the B star with narrow ones - what if the B star isn’t the normal star that Rivinius and his colleagues assume it to be? That could mean the star’s mass is wrong and throw out the mass estimate for a third object.
 
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"HR 6819 - das bislang nächste Schwarze Loch"

Oder doch nicht? Zweifel an der Interpretation gab es ja schon im Mai. Der SL Hypothese wird jetzt auch in einer neuen Arbeit von Gies & Wang von der Georgia State University widersprochen:

Casting Doubt on a Nearby Black Hole

A few months ago, scientists announced the indirect detection of the nearest black hole to Earth. But another team is now suggesting a different explanation for this stellar puzzle.

The Hα Emission Line Variations of HR 6819

The star system HR 6819 was recently proposed by Rivinius et al. as the site of the nearest example of a stellar-mass black hole. Their spectra show evidence of two components: a B3 III star in a 40 day orbit and a stationary B-emission line star. Based upon the orbital mass function and the lack of evidence of a spectral component with reflex orbital motion, Rivinius et al. suggested that HR 6819 is a triple system consisting of an inner B3 III star plus black hole binary orbited by a distant Be star.

Here we present an alternative model based upon an examination of the Hα emission line in their spectra. We show that the emission line displays the small reflex motion expected for the companion in the inner orbit and shows variations in profile shape related to orbital phase. This indicates that HR 6819 is a binary system consisting of a massive Be star and a low-mass companion that is the stripped down remnant of a former mass donor star in a mass transfer binary.


Gies+Wang.jpg

Observed and fitted radial velocity curves for the B3 III star (filled circles) and the disk surrounding the Be star (open circles). The evident orbital motion suggests the two stars comprise a binary system.
Credit: Gies & Wang 2020
 

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Wenn HR 6819 mit einer Entfernung von 1120 +- 20 Lj ausscheidet, dann wäre stattdessen A0620-00 in einer Entfernung von 3000 +- 300 Lj jetzt wieder der nächste Kandidat.

Siehe List of nearest black holes

Aber nota bene:

Most black holes are thought to be solitary and not in a binary (or more) system. However, it is nearly impossible to detect such a black hole aside from measuring its gravitational distortions on the light from visually nearby objects. Black holes in binary systems, despite constituting a minority of all black holes, are much easier to detect.
 
Moin,

auf jeden Fall eine spannende Sache. Egal welche Erklärung sich final als zutreffend erweist, die Entwicklung zu verfolgen ist auf jeden Fall mehr als spannend.

CS
Jörg
 
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