STScI: New Clues to the Star that Wouldn’t Die

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STScI: New Clues to the Star that Wouldn’t Die

Post by bystander » Thu Aug 02, 2018 6:05 pm

Astronomers Uncover New Clues to the Star that Wouldn’t Die
NASA | STScI | HubbleSite | 2018 Aug 02
Eta Carinae Outburst.jpg
Illustration: NASA, ESA, and A. Feild (STScI); Science: NSF and AURA
It takes more than a massive outburst to destroy the mammoth star Eta Carinae, one of the brightest known stars in the Milky Way galaxy. About 170 years ago, Eta Carinae erupted, unleashing almost as much energy as a standard supernova explosion.

Yet that powerful blast wasn’t enough to obliterate the star, and astronomers have been searching for clues to explain the outburst ever since. Although they cannot travel back to the mid-1800s to witness the actual eruption, they can watch a rebroadcast of part of the event — courtesy of some wayward light from the explosion. Rather than heading straight toward Earth, some of the light from the outburst rebounded or “echoed” off of interstellar dust, and is just now arriving at Earth. This effect is called a light echo.

The surprise is that new measurements of the 19th-century eruption, made by ground-based telescopes, reveal material expanding with record-breaking speeds of up to 20 times faster than astronomers expected. The observed velocities are more like the fastest material ejected by the blast wave in a supernova explosion, rather than the relatively slow and gentle winds expected from massive stars before they die.

Based on the new data, researchers suggest that the 1840s eruption may have been triggered by a prolonged stellar brawl among three rowdy sibling stars, which destroyed one star and left the other two in a binary system. This tussle may have culminated with a violent explosion when Eta Carinae devoured one of its two companions, rocketing more than 10 times the mass of our Sun into space. The ejected mass created gigantic bipolar lobes resembling the dumbbell shape seen in present-day images.

Astronomers Blown Away by Historic Stellar Blast
Gemini Observatory | 2018 Aug 02

Light-Echoes from the Plateau in Eta Carinae’s Great Eruption Reveal a Two-Stage Shock-Powered Event - Nathan Smith et al
  • Monthly Notices of the RAS (submitted 25 May 2018) (preprint)
Exceptionally Fast Ejecta Seen in Light Echoes of Eta Carinae’s Great Eruption - Nathan Smith et al
  • Monthly Notices of the RAS (submitted 13 Mar 2018) (preprint)
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Re: STScI: New Clues to the Star that Wouldn’t Die

Post by Ann » Sun Aug 05, 2018 8:22 pm

Hugely interesting, but also confusing. I wasn't really able to understad the graphics. But Astronomy Now provided a very nice explanation:

Astronomy Now wrote:

Smith and Armin argue Eta Carinae likely started out as a triple star system with two massive stars orbiting close together and a third star farther away. When the more massive of the two closely orbiting suns neared the end of its life, it began to expand, allowing the slightly less massive star to suck in an enormous amount of material.
Okay, that's pictures 1 and 2.
That star could swell to about 100 solar masses, in the process stripping away the dying sun’s outer atmosphere and leaving an exposed helium core about 30 times more massive than the Sun.
Picture 3.
That mass transfer would have changed the gravitational architecture of the system, allowing the helium-core star to move away from its huge partner, so far, in fact, that it eventually interacted with the outer third star, kicking it inward. That star finally crashed into the supermassive star at the heart of the triple system in a cataclysmic merger.
Picture 4.
In its initial stages, ejected material moved relatively slowly as the two stars spiralled closer and closer together.
Picture 5.
When the stars finally merged, debris was blown away 100 times faster, catching up and ramming into the slower-moving material and generating the light seen in Eta Carinae’s eruption.

The helium-core star, meanwhile, ended up in an elliptical orbit that carries it through the giant central star’s outer atmosphere every five-and-a-half years, generating X-rays and shock waves.
Picture 6.

Okay, I get it! Now I understand what probably happened to Eta Carinae! :D

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Re: STScI: New Clues to the Star that Wouldn’t Die

Post by BDanielMayfield » Mon Aug 06, 2018 12:37 am

Excellent theory!

Don't miss the impressive video included along with the 6 framed illustration found in the Hubblesite news release here:
bystander wrote:
Thu Aug 02, 2018 6:05 pm
Astronomers Uncover New Clues to the Star that Wouldn’t Die
NASA | STScI | HubbleSite | 2018 Aug 02
And from that article:
The mass transfer alters the gravitational balance of the system, and the helium-core star moves farther away from its monster sibling. The star travels so far away that it gravitationally interacts with the outermost third star, kicking it inward. After making a few close passes, the star merges with its heavyweight partner, producing an outflow of material.

In the merger’s initial stages, the ejecta is dense and expanding relatively slowly as the two stars spiral closer and closer. Later, an explosive event occurs when the two inner stars finally join together, blasting off material moving 100 times faster. This material eventually catches up with the slow ejecta and rams into it like a snowplow, heating the material and making it glow. This glowing material is the light source of the main historical eruption seen by astronomers a century and a half ago.

Meanwhile, the smaller helium-core star settles into an elliptical orbit, passing through the giant star’s outer layers every 5.5 years. This interaction generates X-ray emitting shock waves.
Since the remaining smaller star passes through the primary's outer envelope once each 5.5 year orbit the orbit must decay over time. Has any shortening of Eta Carina's orbital period been observed?

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