ESO: ALMA Catches Beautiful Outcome of Stellar Fight

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ESO: ALMA Catches Beautiful Outcome of Stellar Fight

Post by bystander » Wed Feb 05, 2020 5:38 pm

ALMA Catches Beautiful Outcome of Stellar Fight
ALMA | ESO | NAOJ | NRAO | 2020 Feb 05
Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, have spotted a peculiar gas cloud that resulted from a confrontation between two stars. One star grew so large it engulfed the other which, in turn, spiralled towards its partner provoking it into shedding its outer layers.

Like humans, stars change with age and ultimately die. For the Sun and stars like it, this change will take it through a phase where, having burned all the hydrogen in its core, it swells up into a large and bright red-giant star. Eventually, the dying Sun will lose its outer layers, leaving behind its core: a hot and dense star called a white dwarf.

“The star system HD 101584 is special in the sense that this ‘death process’ was terminated prematurely and dramatically as a nearby low-mass companion star was engulfed by the giant,” said Hans Olofsson ...

Thanks to new observations with ALMA, complemented by data from the ESO-operated Atacama Pathfinder EXperiment (APEX), Olofsson and his team now know that what happened in the double-star system HD 101584 was akin to a stellar fight. As the main star puffed up into a red giant, it grew large enough to swallow its lower-mass partner. In response, the smaller star spiralled in towards the giant’s core but didn’t collide with it. Rather, this maneuver triggered the larger star into an outburst, leaving its gas layers dramatically scattered and its core exposed. ...

HD 101584: Circumstellar Characteristics and Evolutionary Status ~ H. Olofsson et al
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Re: ESO: ALMA Catches Beautiful Outcome of Stellar Fight

Post by Ann » Wed Feb 05, 2020 7:52 pm

Fascinating. I checked up star HD 101584. Its spectral class is F0Iape. The "F0Ia" suggests that this star is a magnificent supergiant, and the "pe" means peculiar. I'll say!

Well, according to this star's most uncertain Hipparcos parallax, HD 101584 isn't bright enough to deserve the designation F0Ia. Its luminosity is "only" 750 ± 710 times the luminosity of the Sun, not enough for a star to be called a supergiant. Then again, the Hipparcos parallax is very uncertain, and HD 101584 may be farther away than Hipparcos thought it was. Or, alternatively, HD 101584 really is considerably fainter now than it used to be because it has shed so much mass!

The color of HD 101584 is very interesting. For an F-type supergiant (or at least giant), it is quite blue! All right, it isn't as blue as Canopus, spectral type F0Ib and second-brightest star in the sky, but HD 101584 is certainly much farther away than Canopus, much closer to the band of the Milky Way than Canopus and certainly much more reddened. So a color index of 0.303 ± 0.009 is remarkably blue for HD 101584.

My point is that HD 101584 bears no resemblance to a red giant, colorwise. Maybe it was a red giant until it blew its own outer layers away.

Fascinating! The scenario of a larger star enveloping a smaller companion and making it spiral towards the core of the larger star, triggering an outburst of the larger star and making it dramatically shed much of its outer layers, resembles the suggested scenario that triggered hypernova SN 2006gy.

Of course, when it comes to SN 2006gy, the small star that was (supposedly) engulfed inside its larger companion's outer layers and was made to spiral into the core of its larger companion, was a white dwarf.

Well, in any case, both HD 101584 and SN 2006gy are very fascinating creatures of the stellar zoo!

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Re: ESO: ALMA Catches Beautiful Outcome of Stellar Fight

Post by neufer » Thu Feb 06, 2020 3:52 am

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