Astronomy/cosmology questions...

[Buster's Uncle]

I've seen it - and the one gwilly put up two weeks ago.  -Proxima isn't a discreet star though, IIRC; it a name for the system of three...

[Lorizael]

It's the other way around. Alpha Centauri is the name of the binary star system (with stars A and B), and Proxima Centauri was discovered much later as an orbiting third.

[Buster's Uncle]

Is it still going to be closer in 100 years, then?
 
 

The edge of the universe is closer than scientists previously thought

[Lorizael]

It's currently moving toward us, but I only know that because I looked it up on wikipedia.

[Buster's Uncle]

Did the Wikipedia say what the period was?

[Lorizael]

Best guess is its orbital period around Alpha Centauri is something like half a million years. It will be approaching us for another 27,000 years or so. (I trust Wikipedia for this kind of information because I know what astrophysical databases they're pulling their numbers from.)

[ColdWizard]

IRAS 19312+1950, why?

[gwillybj]

hmmm...

[Lorizael]

IRAS 19312+1950, why?

Stellar models are fiendishly complicated and not something I've studied in depth. The one thing I'll say, which the article talks about, it that the more distant a star is, the more difficult it is to tell if you're seeing the star or the star+interstellar medium of gas and dust in between. Disentangling the two often involves looking at a star in multiple EM bands (radio, optical, IR) and seeing what gets through.

[Rusty Edge]

IRAS 19312+1950, why?

Stellar models are fiendishly complicated and not something I've studied in depth. The one thing I'll say, which the article talks about, it that the more distant a star is, the more difficult it is to tell if you're seeing the star or the star+interstellar medium of gas and dust in between. Disentangling the two often involves looking at a star in multiple EM bands (radio, optical, IR) and seeing what gets through.

Unlike the black and anti stuff in the Universe, this makes a lot of sense to me.

[Lorizael]

Unlike the black and anti stuff in the Universe, this makes a lot of sense to me.

Assuming you mean dark when you say black, I've recently been thinking about a new way to talk about dark matter. Pretend you're a theoretical physicist and you'd like to win a Nobel Prize for discovering a new kind of matter. So you sit down and come up with the completely bonkers idea of matter that interacts only via gravity (but not electromagnetism or any other force). You call this hypothetical stuff gravimatter.

To win your Nobel Prize, you're gonna have to get some experimental/observational scientists to detect it by some means. So how do you test for the presence of gravimatter? Well, you look for regions where there's a lot of gravitational interaction. Unfortunately, because normal matter also interacts via gravity, you can't easily disentangle gravimatter from regular matter. The best way to do so is to play on the key difference between your hypothesized gravimatter and regular matter, which is that regular matter interacts via electromagnetism but gravimatter doesn't.

Because regular matter responds to electromagnetism, collisions convert motion (kinetic energy) into light (thermal energy), which means we can tear gravimatter away from regular matter by looking at regions that are moving very quickly. That is, we can do like the particle physicists do and slam stuff together. When you slam stuff together, the regular matter will slow down and start to glow, but the gravimatter will just keep going. That way, if you detect gravitational interaction where there's no glowing, you can be sure you're looking at gravimatter and not regular matter.

Gravity is weak, though, so you can't really do this in a particle accelerator and expect to find anything. Instead you ask astronomers to look through the universe for cases where this might be happening. The astronomers point their telescopes into space and find this, the Bullet Cluster.



The Bullet Cluster is a collision between two galaxy clusters. The pink-ish red stuff in the middle are x-rays from gas heated by the two clusters ramming into each other. The x-rays emissions are  stuck in the middle where the gas has been slowed down by the massive collision. The blue stuff on the outside, moving away from the center, represents gravitational lensing, which is the degree to which matter gravitationally distorts the image of background objects. There's no red glow where the blue lensing is happening (the colors are totally arbitrary, btw), because there's virtually no regular matter there. The best explanation for why you have lensing without regular matter is gravimatter.

By the strength of the lensing, you can estimate how much of the galaxy cluster is composed of gravimatter. If you guess that this is a typical amount of gravimatter, then you can also predict that gravimatter will probably play a very significant role in the structure of the universe, dictating things like how the galaxy web will form, what sorts of fluctuations you'll see in the CMB, and what kind of rotation curves spiral galaxies will have. And sure enough, gravimatter seems to pop up in all of those places (and more) in the proportions dictated by the Bullet Cluster and similar regions. Congratulations, the Nobel Committee should be along shortly.

[Rusty Edge]

So gravey matter is concentrated in the mash? 

You're pretty good at this! I really hope you find a niche as an author or virtual university professor or planetarium director or something where you can find a broad audience.

[Lorizael]

So gravey matter is concentrated in the mash? 

 

You're pretty good at this! I really hope you find a niche as an author or virtual university professor or planetarium director or something where you can find a broad audience.

Well, I did just start TAing for an introductory astronomy course. We'll see how that goes.

[ColdWizard]

Stellar models are fiendishly complicated and not something I've studied in depth.

Does that mean I can't ask about Yellow Hypergiants?

[Lorizael]

You can certainly ask. I might even know something.