Starship Asterisk*

Rauf wrote: ↑Sat Jun 01, 2024 7:49 am

Ann wrote: ↑Sat Jun 01, 2024 4:43 am
Massive stars form from particularly large disks. It seems likely, at least to me, that large disks are more prone than smaller ones to fragmenting, thus creating massive stars that are born as binaries.

Thanks Ann. But what causes this fragmentations? Gravity from a nearby star, or a black hole? Or maybe radiation and wind from the original star?

The protostellar disk is a fluid. That means there are turbulence and friction and viscosity effects. I don't think "fragmentation" is quite the right way to look at it. Stir some cream into your coffee and you'll see secondary vortexes appear.

Just in case this question was missed earlier (and if it wasn't but just inspired no comments, that's fine!) - are Wolf-Rayet stars the brightest of stars intrinsincally? Supposedly THE brightest star currently known is a Wolf-Rayet (R136a 1), but is it also the case with any Wolf-Rayet compared to stars of similar mass, even luminous blue variables?

Christian G. wrote: ↑Sat Jun 01, 2024 4:56 pm Just in case this question was missed earlier (and if it wasn't but just inspired no comments, that's fine!) - are Wolf-Rayet stars the brightest of stars intrinsincally? Supposedly THE brightest star currently known is a Wolf-Rayet (R136a 1), but is it also the case with any Wolf-Rayet compared to stars of similar mass, even luminous blue variables?

Very good question. Wikipedia has a long list of stars with a luminosity of more than a million solar luminosities.

https://en.wikipedia.org/wiki/List_of_m ... stars#Data

If you look at this list, you can see that the most luminous star known to humanity, according to Wikipedia, is BAT99-98. This is indeed a Wolf-Rayet star of spectral class WN6. The second and fourth most luminous stars are also Wolf-Rayet stars (the fourth being R136a1).

But stars #3, #5, #6, #7, 8# and #9 are other spectral types, five of them O-type stars of luminosity class Ia, one Luminous Blue Variable (eta Carina) and one star of spectral class B0Iae.

By the way, the background colors behind the star names used to designate spectral classes are a mess! Purple supposedly means a Wolf-Rayet star, and O-type stars should have a blue background. But the stars in in 3rd and 6th place, stars in in the Triangulum Galaxy, supposedly belong to spectral classes O4Ia (so that the star names should be written on a blue background), but instead they are written on a purple background, as if the stars were Wolf-Rayet stars.

By the way: The star in 3rd place, [BMS2003] 867, supposedly belongs to spectral class O4Iab. That's impossible! The "b" in luminosity class "Iab" means a bright supergiant, but not the very brightest type of supergiant. But this particular star is supposedly the third most luminous star known to humanity? Get rid of that "b", because in this context it is impossible!

But in any case, this is a fun list to look at, and you will find many Wolf-Rayet stars among the most luminous stars known to humanity.

Ann

Chris Peterson wrote: ↑Sat Jun 01, 2024 4:15 pm

Rauf wrote: ↑Sat Jun 01, 2024 7:49 am

Ann wrote: ↑Sat Jun 01, 2024 4:43 am
Massive stars form from particularly large disks. It seems likely, at least to me, that large disks are more prone than smaller ones to fragmenting, thus creating massive stars that are born as binaries.

Thanks Ann. But what causes this fragmentations? Gravity from a nearby star, or a black hole? Or maybe radiation and wind from the original star?

The protostellar disk is a fluid. That means there are turbulence and friction and viscosity effects. I don't think "fragmentation" is quite the right way to look at it. Stir some cream into your coffee and you'll see secondary vortexes appear.

I like this video of primary and secondary vortexes:


I found this video of what happens when you pour cream into coffee:


Someone has said that when you pour cream into coffee, you can see the evolution of the Universe. What we find when we first start pouring cream is turbulence, but almost immediately structure appears. We can see the structure evolving, then dissolving, until the coffee and the cream are completely mixed together.

This is what is going to happen to our Universe. We live in the sprightly youth of the Universe, since, after all, we believe that the Universe is only three times older than the Earth itself. But already the Universe is "winding down", and star formation has turned into a trickle of what it was in the cosmic dawn. When the Universe is twice its current age, perhaps no brilliant massive stars like the beacons of Orion will be born any more. More Sunlike stars will die than be born, until, perhaps a trillion years from now, only the little red dwarfs and the black holes will remain. After another trillion years, most of the red dwarfs will have died too, and eventually only the black holes remain, until they, too, evaporate and die.

And then the entire Universe will be a soup of a homogeneous density and temperature, from which no more energy can be extracted and nothing more can happen.


This is the end of everything. Drink up now.

Ann

What would happen with the solar system if we were within 20 lightyears from a wolf rayet star and the bubble was expanding into it?

beryllium732 wrote: ↑Tue Jun 04, 2024 11:49 am What would happen with the solar system if we were within 20 lightyears from a wolf rayet star and the bubble was expanding into it?

Nothing. The bubble is a hard vacuum.

Chris Peterson wrote: ↑Tue Jun 04, 2024 12:48 pm

beryllium732 wrote: ↑Tue Jun 04, 2024 11:49 am What would happen with the solar system if we were within 20 lightyears from a wolf rayet star and the bubble was expanding into it?

Nothing. The bubble is a hard vacuum.

Ok I see that's cool to know! What if we replaced the Alpha Centauri system with a Wolf Rayet star would we be impacted?

beryllium732 wrote: ↑Tue Jun 04, 2024 4:05 pm

Chris Peterson wrote: ↑Tue Jun 04, 2024 12:48 pm

beryllium732 wrote: ↑Tue Jun 04, 2024 11:49 am What would happen with the solar system if we were within 20 lightyears from a wolf rayet star and the bubble was expanding into it?

Nothing. The bubble is a hard vacuum.

Ok I see that's cool to know! What if we replaced the Alpha Centauri system with a Wolf Rayet star would we be impacted?

I don't think the outgassing and ejected material is likely to ever be an issue. At some point it's problematic from a radiation standpoint to be too close to this sort of object, though.