APOD: Dragon's Egg Bipolar Emission... (2024 Apr 24)

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APOD: Dragon's Egg Bipolar Emission... (2024 Apr 24)

Post by APOD Robot » Wed Apr 24, 2024 4:09 am

Image Dragon's Egg Bipolar Emission Nebula

Explanation: How did a star form this beautiful nebula? In the middle of emission nebula NGC 6164 is an unusually massive star. The central star has been compared to an oyster's pearl and an egg protected by the mythical sky dragons of Ara. The star, visible in the center of the featured image and catalogued as HD 148937, is so hot that the ultraviolet light it emits heats up gas that surrounds it. That gas was likely thrown off from the star previously, possibly the result of a gravitational interaction with a looping stellar companion. Expelled material might have been channeled by the magnetic field of the massive star, in all creating the symmetric shape of the bipolar nebula. NGC 6164 spans about four light years and is located about 3,600 light years away toward the southern constellation Norma.

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Re: APOD: Dragon's Egg Bipolar Emission... (2024 Apr 24)

Post by Ann » Wed Apr 24, 2024 6:25 am

Yes, that's a nice APOD! I particularly like the faint blue "outer halo or nebula". Blue gas does not appear naturally in space, so we have to assume that the blue gas is green OIII emission that has been mapped as blue.

The ionizing star HD 148937 figured prominently in Sky & Telescope a week ago with some exciting information about this star, information that is absent from the APOD caption. HD 148937 appears to be a "collisional product", a stellar merger! It might be a later version of V838 Monocerotis!

Wikipedia wrote about V838 Monocerotis:

V838 Monocerotis (Nova Monocerotis 2002) is a spectroscopic binary star system in the constellation Monoceros about 19,000 light years (6 kpc) from the Sun. The previously unremarked star was observed in early 2002 experiencing a major outburst, and was one of the largest known stars for a short period following the outburst. Originally believed to be a typical nova eruption, it was then identified as the first of a new class of eruptive variables known as luminous red novae. The reason for the outburst is still uncertain, but is thought to have been a merger of two stars within a triple system.
Sky & Telescope wrote about HD 148937:

In stellar astronomy, sometimes 1 + 1 = 1.

Astronomers haven’t lost their grip on math. The latest evidence for this calculus comes from the nebula NGC 6164/6165. At its heart lies the binary HD 148937, which comprises a pair of hot, massive O-type stars.

But not too long ago, there were likely three stars
Under the right circumstances, these stars can actually spiral in and merge with each other in a violent splash. When they do, they throw off gas that cools and creates dust, temporarily shrouding the new star. This event is called a red nova (red because of the dust’s effect).
Massive stars like these aren’t supposed to have strong surface magnetic fields, because they don’t have the same churning in their interiors that sustains magnetic fields in stars like the Sun. Yet approximately 7% of massive stars have observable fields.

A stellar merger, on the other hand, would stir up the inside of a newly created star, creating a strong magnetic field. The new star would spin abnormally fast, too, and it would look “too young” for its mass — and both of these are properties of HD 148937’s primary...

So, to summarize: Both HD 148937 and V838 Monocerotis are believed to have started out as 3 body systems, where two of the components merged. But in the case of V 838 Monocerotis, the merger happened "just yesterday" - well, we saw it happen in 2002 - but in the case of HD 148937, the merger took place "several thousand years ago", according to Sky & Telescope. That would give the merger product time to settle down and become a hot O-type star like HD 148937, not an M (or even L!) type newborn cool supergiant like V838 Monocerotis.

(And if you object and say that the merger that created V838 also happened several thousand years ago, some 19,000 years ago to be more exact, astronomers don't date nearby novas and supernovas that way. These novas and supernovas are said to have happened on the date when we first observed them.)

So anyway: When three bodies are involved, you don't know what will happen.

3 body problem Tatiana.png

And if you dare, open this 54 MB gif, which shows, according to Wikipedia, 20 examples of periodic solutions to the three-body problem.

I guess the orbits of the stars that created HD 148937 and V838 Monocerotis were not so regular and periodic.

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Re: APOD: Dragon's Egg Bipolar Emission... (2024 Apr 24)

Post by johnnydeep » Wed Apr 24, 2024 12:59 pm

Always nice to see a reference to the book Dragon's Egg by Robert L. Forward, but the O-type stellar "egg" here is not the same type of egg as the titular star of the book, which is a neutron star. Though HD 148937 may well become a neutron star in a few million years as the end product of a supernova.
"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."{ʲₒʰₙNYᵈₑᵉₚ}

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Re: APOD: Dragon's Egg Bipolar Emission... (2024 Apr 24)

Post by VictorBorun » Wed Apr 24, 2024 1:12 pm

Dragon's Egg Bipolar Emission... (2024 Apr 24).jpg
Dragon's Egg Bipolar Emission... (2024 Apr 24) 2.jpg
Click to view full size image 1 or image 2
to my eye a blue (OIII, right?) jellyfish swimming rightward from the star breakes the bipolarity
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