For Questions That Don't Merit Their Own Thread

[JoeSchmuckatelli]

1 hour ago, SOXBLOX said:

the stars which you can see distinctly are foreground stars; they're part of the Milky Way

Slapping myself across the forehead...

8o

Of COURSE they are foreground stars... They'd have to be. 

SMH - I'm an idiot sometimes! 

 

Thanks! 

 

Found this on the wiki - it's pretty cool 

https://upload.wikimedia.org/wikipedia/commons/2/2b/Centaurus_A_EN.webm

 

Edited September 6, 2021 by JoeSchmuckatelli

[SOXBLOX]

4 hours ago, JoeSchmuckatelli said:

Slapping myself across the forehead...

8o

Of COURSE they are foreground stars... They'd have to be. 

SMH - I'm an idiot sometimes! 

 

Thanks! 

 

Found this on the wiki - it's pretty cool 

https://upload.wikimedia.org/wikipedia/commons/2/2b/Centaurus_A_EN.webm

 

No worries! And that video is cool. I think it's fascinating how much we can tell about something so far away just by looking at it in all wavelengths.

[JoeSchmuckatelli]

Amateur Astronomer accidently finds exceedingly rare star while playing CS

This Very Weird ‘Accidental’ Star Could Help Reveal the Secrets of the Cosmos (msn.com)

 

[kerbiloid]

Raxxla???

[magnemoe]

3 hours ago, JoeSchmuckatelli said:

Amateur Astronomer accidently finds exceedingly rare star while playing CS

This Very Weird ‘Accidental’ Star Could Help Reveal the Secrets of the Cosmos (msn.com)

 

Yes this is very cool, current theories is that most first generations stars was massive and therefor short lived. This might be incorrect and if we find an red dwarf so old or older it would be even cooler. 
 

[JoeSchmuckatelli]

And more Planet 9 stuff from the guy who demoted Pluto:   https://www.nbcnews.com/science/space/astronomers-are-still-looking-elusive-planet-9-rcna1872

@magnemoe@magnemoe re: low methane brown dwarfs - is there a possibility of "Gen 1a" stars -  that might have formed in the gaps and remnants of the earliest Gen 1 that formed and collapsed or blew up before the main body of Gen 1's did their thing? 

[JoeSchmuckatelli]

Is there a way to distinguish redshift of a galaxy due to expansion from redshift due to the relative motion?

i.e. If there were two galaxies in the Coma Cluster, one moving 500 km/s toward the Milky Way and another moving 500 km/s away - could we know if they were passing each other and equidistant from us (if imaged at the right time)? 

Edited September 8, 2021 by JoeSchmuckatelli

[mikegarrison]

22 hours ago, JoeSchmuckatelli said:

Is there a way to distinguish redshift of a galaxy due to expansion from redshift due to the relative motion?

They are the same thing.

The only difference is that random relative motion should be half blue and half red. If it's biased toward red (and it is), then that means expansion.

[JoeSchmuckatelli]

For all you particle physicists out there:  1st sign of elusive 'triangle singularity' shows particles swapping identities in mid-flight (msn.com)

 

 

---   ---   ---

 

@mikegarrison 'They are the same thing'

--- This is one of those things that's hard to grasp.  I've googled around and found I'm still a bit confused.

Take Messier 90 (Hubble Spies Curious Galaxy Moving a Little Closer | NASA)  

It's part of the Virgo Cluster, approximately 60 million light years away.  Much of the cluster is moving away from us (redshifted) but Messier 90 is blueshifted.  

Quote

This increases the frequency of the light and shifts it towards the blue end of the spectrum. As our universe is expanding, almost all of the galaxies we see in the universe are moving away from us, and we therefore see their light more towards the red end of the spectrum, known as redshift. Messier 90, however, appears to be a rare exception

If expansion is the rule, then I would assume that all galaxies in the cluster are moving away - but that there might be some distinction between relative motion within the cluster.  I just don't read the article that way... it seems like they are saying that Messier 90 is actually moving toward us.

Is this just bad writing, or is it possible that Messier 90 is fast enough to overcome the expansion and is literally approaching the Milky Way?

[Terwin]

2 hours ago, JoeSchmuckatelli said:

@mikegarrison 'They are the same thing'

--- This is one of those things that's hard to grasp.  I've googled around and found I'm still a bit confused.

If an object is moving away from earth, then it has a red-shift, if it is moving towards earth, it has blue-shift.  Higher velocities relative to earth have larger shifts.

*Only* the total velocity matters, for example, a rotating galaxy that is moving away from us a 100kps with a max rotational velocity of 40 kps at the edges will have some bits with a 60kps red-shift on the 'towards us' side, grading up to 100kps of red-shift in the middle, then up to 140kps of red-shift on the 'away from us' side.

 

Edited September 10, 2021 by Terwin
typo

[kerbiloid]

Got it. Gargantua should be reddish-blue, they lied to us.

[K^2]

On 9/8/2021 at 1:03 PM, JoeSchmuckatelli said:

Is there a way to distinguish redshift of a galaxy due to expansion from redshift due to the relative motion?

On 9/9/2021 at 11:26 AM, mikegarrison said:

They are the same thing.

Technically correct, but I think this caveat is worth mentioning. They are completely identical if the expansion is uniform, but since universe is expanding at an accelerated rate, we can directly probe that acceleration. Of course, if all you are looking at is light, it's no help, but accelerated expansion will impact massive particles slightly differently. So if you could measure both from the same source, say light and a neutrino burst from the same event, and you knew initial energies for each, you could work out what the actual velocity of the source should be if it's only due to expansion and get motion relative to that. It'd be a very indirect measurement and rely on acceleration being uniform over relevant time frames, so not applicable to most distant objects, but it's a way to, at least in theory, distinguish between expansion and relative motion. In practice, I don't think we have means to do this quite yet.

Also, the distinction here is a bit of an Occam's razor one. There is no true physical difference, and a contrived example can be made where you get fooled, but it's a bit like equivalence of gravity and acceleration. Sure, you can't really distinguish between the two, but if along with "gravity" you noted a rather strong Coriolis effect, you're probably sitting inside a centrifuge and not on a surface of a planet.

[kerbiloid]

A strange source of radiowave emission is detected at the center of the Galaxy.

Highly polarized.
Sometimes emitting for weeks, sometimes hiding with irregular intervals, from a day to months. 

They were studying it in 2020, the signal level was varying by 100 times.

They were looking at it in IR and UV by Swift and Chandra. The source didn't emit in these ranges of spectrum.

Unlike pulsars and magnetars, it's not periodic.

It could be a GCRT process in galactic center (they both emit polarized radiowaves but no X-rays), but unlike GCRT it's non-periodicm and the sequence of flashes differs.

https://translate.google.com/translate?hl=&sl=ru&tl=en&u=https://habr.com/ru/news/t/577408/

https://arxiv.org/abs/2109.00652

[JoeSchmuckatelli]

13 hours ago, kerbiloid said:

GCRT

Thanks for the link and info - you introduced me to a new term. 'Galactic Center Radio Transient' 

 

Never heard of those before 

 

 

... 

 

 

Okay - I have an esoteric 'expansion' question. 

I've often read people writing about an image of a galaxy 1million LY away, that we are seeing the galaxy as it was a million years ago. 

But are we?

If expansion is happening to space, isn't it also happening to time?  

The light from the galaxy starts heading towards where we will be when it gets there, and during the transit the space and time between us expands... We say the light is redshifted - but is it also timeshifted? 

What would that look like? 

[Admiral Fluffy]

Quick question, before continuing on to the one above me, 

If you dropped a piece of paper on a 1G planet with no atmosphere, from high enough, could you skewer it on a rock?

[JoeSchmuckatelli]

1 hour ago, Admiral Fluffy said:

Quick question

Yes - but you are unlikely to find a no atmosphere planet at 1g 

[DDE]

5 hours ago, JoeSchmuckatelli said:

Yes - but you are unlikely to find a no atmosphere planet at 1g 

Well, you might... but then the piece of paper would be vaporized by sunlight long before it reaches the red-hot rock.

[kerbiloid]

(To look smart, too)

If the 1g planet has survived the red giant phase of the star, thus has lost its own atmosphere, was surrounded by the captured hydrogen instead, then it had escaped, then we can have a cool 1g airless planet, enough safe to land a paper plane.

[ARS]

Is there any specific reason why Soviet/ Russian Navy have a habit to paint the deck of their warships red? (Most of the time, especially on post-WW2 and cold war-era warship) 

[kerbiloid]

Because the NATO paints it blue.

Edited September 13, 2021 by kerbiloid

[SOXBLOX]

I think it was just red lead rust-proofing paint. Lots of navies use or used it, they just added topcoats.

[DDE]

52 minutes ago, SOXBLOX said:

I think it was just red lead rust-proofing paint. Lots of navies use or used it, they just added topcoats.

 

2 hours ago, ARS said:

Is there any specific reason why Soviet/ Russian Navy have a habit to paint the deck of their warships red? (Most of the time, especially on post-WW2 and cold war-era warship) 

They are all red on the inside:

https://m.youtube.com/watch?v=4oXlfIex1Hg&t=1m30s

[SunlitZelkova]

A couple of questions in regards to a story I am writing to use as background for things in two games (KSP and a post-WWII milsim)-

1. In nuclear weapons development, does one need to go "atomic bomb first, then hydrogen bomb" or can you jump straight to hydrogen bomb? Specifically within the context of Japan's nuclear industry.

2. How long would it take to convert an orbital launch vehicle into an ICBM (namely the M-V rocket), assuming national survival level urgency (ZiS-30 tank destroyer urgency)? Specifically, time to first test flight.

3. If mission control can't "keep the lights on" (that is, NASA is bankrupt and the Texas electrical grid has completely ceased to operate) could astronauts "fly back" on their own (with little to no aid from mission control)? Namely from a Mars or Moon base.

[DDE]

24 minutes ago, SunlitZelkova said:

3. If mission control can't "keep the lights on" (that is, NASA is bankrupt and the Texas electrical grid has completely ceased to operate) could astronauts "fly back" on their own (with little to no aid from mission control)? Namely from a Mars or Moon base.

I'd give a tentative "yes". It would depend heavily on the design of the navigation systems in place; however, the math would be familiar to the wing-wearing astronauts in the crew, and with an accurate emphemeris and working astronavigation (similar to Apollo's sextant system) they'd have a fair chance of working out autonomous procedure. Not saying it would be easy, but a conjunction-class Mars mission would have enough time.

I'm also of the opinion we're going to see a general move in that direction: communication delay would make the crew too apprehensive to be as reliant on Mission Control as they are on LEO and Moon missions. You can already see this in Russian vs NASA/ESA culture: with entire orbits outside ground comms range, cosmonaut crews (in my case, Sergei Ryazanskyi) admit to ignoring, and even lying to, MMC/Zarya if they think they themselves know better.

32 minutes ago, SunlitZelkova said:

1. In nuclear weapons development, does one need to go "atomic bomb first, then hydrogen bomb" or can you jump straight to hydrogen bomb? Specifically within the context of Japan's nuclear industry.

Define "go". Since all thermonuclear bombs include a nuclear first stage, "going" atomic first makes sense as an early win. Yes, you can keep developing a hydrogen bomb on top of that - since the test ban treaties, techniques for adequate subcritical testing have been developed, you'd need to work around CBTO seismic sensors if you want to keep it completely hush-hush. Since we're talking about modern Japan, the generic and nuclear power-related capabilities would all be present; whether specific weapons-related competencies can be acquired is... above my paygrade.

[monophonic]

21 minutes ago, SunlitZelkova said:

A couple of questions in regards to a story I am writing to use as background for things in two games (KSP and a post-WWII milsim)-

1. In nuclear weapons development, does one need to go "atomic bomb first, then hydrogen bomb" or can you jump straight to hydrogen bomb? Specifically within the context of Japan's nuclear industry.

2. How long would it take to convert an orbital launch vehicle into an ICBM (namely the M-V rocket), assuming national survival level urgency (ZiS-30 tank destroyer urgency)? Specifically, time to first test flight.

3. If mission control can't "keep the lights on" (that is, NASA is bankrupt and the Texas electrical grid has completely ceased to operate) could astronauts "fly back" on their own (with little to no aid from mission control)? Namely from a Mars or Moon base.

1. In hydrogen bombs the heat and pressure necessary to start fusion is reached with a small fission device. So no. There is also the intermediate level of boosted fission device, where a small amount of fusionable material injected into the fission core provides a significant boost to the energy output.

2. Depends on the exact technology level, namely how difficult it is to reconfigure the guidance system, but not very much. You may lose some range or be limited to longer flight times as the airframe may not be strong enough to fly the optimal trajectory. Specifically for the M-V rocket, though, it has been suspected to be easily weaponized.

3. @DDE gave a much better answer above than I ever could.