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Forum » SpaceEngine » Science and Astronomy Discussions » Science and Astronomy Questions
Science and Astronomy Questions
WatsisnameDate: Tuesday, 31.12.2013, 23:16 | Message # 226
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From the universe size thread,
Quote SpaceEngineer
With density of 10 galaxies per cubic megaparsec, it have 10 trillion galaxies (1013). Too small, I must make it few billions time bigger in each dimension :biggrin:


This got me wondering, what is the real number density of galaxies in the universe (at present)?





 
HarbingerDawnDate: Tuesday, 31.12.2013, 23:41 | Message # 227
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Quote Watsisname ()
what is the real number density of galaxies in the universe (at present)?

42





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DoctorOfSpaceDate: Tuesday, 31.12.2013, 23:51 | Message # 228
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Quote HarbingerDawn ()
42








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WatsisnameDate: Wednesday, 01.01.2014, 00:07 | Message # 229
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That can't be right, that answer wasn't supposed to be revealed until after Earth is demolished to make room for that hyperspace bypass. Oh wait, FFF--




 
JonasTheRomanDate: Wednesday, 19.03.2014, 18:55 | Message # 230
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Hello guys!

So I've just registered to be able to ask you about a thing that I found in SE (it's an amazing program btw!).

I visited Alnilam in the constellation of Orion and saw, that in SE this blue supergiant star is being orbited by a black hole, even very close.
Is this possible in reality? Wikipedia says nothing about a black hole in Alnilam's orbit, but I doubt Wikipedia is the best source for astronomic questions. Ingame the black hole isn't marked as a real object, but why it was generated orbiting an real object then?

I'm sorry if this question is too trivial, but I'm not that well informed about astronomy.
We just don't do astronomy in school, which is a pity. cry
 
apenpaapDate: Wednesday, 19.03.2014, 19:47 | Message # 231
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SE has only a few stars catalogued as binaries. Almost all catalog stars are entered as if they were solitary, even though about 60% of stars is binary. For this reason, it turns some of the catalog stars into binary systems. Black holes get generated for them sometimes.




I occasionally stream at http://www.twitch.tv/magistermystax. Sometimes SE, sometimes other games.
 
JonasTheRomanDate: Wednesday, 19.03.2014, 20:17 | Message # 232
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Ok, thank you.
So this means black holes can theoretically orbit a star in reality? Wouldn't it just attract the star and absorb it?
 
apenpaapDate: Wednesday, 19.03.2014, 20:34 | Message # 233
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A black hole is no different from any other gravity source, really. If there was a 1 solar mass black hole at the place the Sun is, all planets would still continue in their normal orbits. A blue giant, while sparser than main class stars, still has a decent amount of gravity at the surface, so a black hole would have to be really close to actually suck up material from the star.




I occasionally stream at http://www.twitch.tv/magistermystax. Sometimes SE, sometimes other games.
 
midtskogenDate: Wednesday, 19.03.2014, 20:36 | Message # 234
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Quote JonasTheRoman ()
So this means black holes can theoretically orbit a star in reality? Wouldn't it just attract the star and absorb it?

No more than a star of the same mass would.





NIL DIFFICILE VOLENTI
 
JonasTheRomanDate: Wednesday, 19.03.2014, 21:31 | Message # 235
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This seems logical to me, thank you. I actually didn't thought this way. surprised
I just checked the system, the star is even 8000 Earth masses heavier than the black hole.

I have another question. I often spotted huge stars which are oddly shaped, like this:

What is the reason for this? Shouldn't the star just be round or oval? I never heard of such stars, but they are quite common in SE.

Attachments: 6398310.jpg(126Kb)


Edited by JonasTheRoman - Wednesday, 19.03.2014, 21:34
 
apenpaapDate: Wednesday, 19.03.2014, 21:39 | Message # 236
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Well, those bumps are huge convection cells, which red giants apparently have. The reason they're so pronounced and distort the shape of the star is that red giants are extremely sparse (they're about as dense as Earth's atmosphere at 100 km height) and therefore have extremely low surface gravity, allowing some deviation from a spherical shape. Red giants (at least some of them) might very well look like that in real life.




I occasionally stream at http://www.twitch.tv/magistermystax. Sometimes SE, sometimes other games.
 
JonasTheRomanDate: Wednesday, 19.03.2014, 21:47 | Message # 237
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Thank you for that explanation! smile
It's odd to think about such sparse stars.
SE and this forum are really broadening my mind!
 
midtskogenDate: Wednesday, 19.03.2014, 22:08 | Message # 238
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Here's an actual photo of Betelgeuse's surface:

Red giants also likely have an extended and changing atmosphere reaching out several times the visual surface. Some direct evidence exists in photographs of Betelgeuse, such as:




These clouds are of course very thin, vacuum for most purposes.





NIL DIFFICILE VOLENTI
 
HarbingerDawnDate: Thursday, 20.03.2014, 01:44 | Message # 239
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Quote JonasTheRoman ()
So this means black holes can theoretically orbit a star in reality?

Of course, though technically there's no such thing as one object orbiting another, as gravity works both ways. Best to describe them orbiting each other when their masses are relatively close, and describing which is primary and which is secondary.

Anyway, for a real life example of a star-black hole binary with a stellar primary, look up Cygnus X-1.





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Laine115Date: Monday, 31.03.2014, 16:07 | Message # 240
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Why are galaxies flat instead of being spherical?




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