Astronomy Trivia Challenge: Can You Answer These Questions About the Night Sky?

[marcus]

Originally posted by Labguy
Without "matherizing", which I hate, I would have to say that the radius of curvature of the photon at 4.5 miles from the "center" would be 4.5 miles, in an attempt to obtain a circular orbit. Your 4.5 miles just happens to be 1.5 R_S.

That is right. If a black hole has schwarzschild radius 3 miles then the only distance at which light can go in circular orbits is 4.5 miles.

(this is for the ordinary case of non-rotating uncharged holes.)

The radius of the so-called "photon sphere" around the black hole, where light can orbit, is always 1.5 times the schw. radius.

Your turn Labguy.

(My son once took an introduction to astronomy course where the professor liked to tell students that if you put your head in the photosphere of a BH you would be able to see the back of your own head. for some reason that idea was popular with the students.)

 

[chroot]

Originally posted by marcus
The radius of the so-called "photon sphere" around the black hole, where light can orbit, is always 1.5 times the schw. radius.

Woops!

- Warren

 

[marcus]

Originally posted by chroot
But wait, a light ray moving tangentially along the event horizon, will, in fact, orbit the black hole.

- Warren

Not according to the professors and textbooks and stuff. It will dive into the black hole and head for the singularity----that is, if it starts off tangential along the event horizon.

The only altitude where it can orbit is in the "photon sphere" radius 1.5 times schwarzschild.

However it is still interesting to consider projecting a horizontal ray of light a few feet above the event horizon and asking about its initial radius of curvature.

It won't be the schwarzschild radius because then it would orbit, which it doesnt.

but it might initially be a nice fraction of the schwarzsch. radius,
like 2/3 or 1/2 of it----or it might be nearly zero

The first case would mean that for somebody suspended near the surface of a 3 trillion miles radius hole (with its earth-like gee) light seems to go STRAIGHT in his immediate surroundings. It hardly bends at all, or only imperceptibly. I am referring back to maybe 5 or 6 posts ago.
On the other hand the curve might be very tight and the light might take an immediate nosedive into the event horizon, when it is close---in which case the optics would be weird.

Either way it doesn't just orbit along the event horizon. But its interesting to try to figure out what it does.

 

[marcus]

Originally posted by chroot
Woops!

- Warren

Yeah, I know.
They are tricky objects.

Anyway we must not forget that it is now Labguys turn!

He will undoubtably pose us a question that will be a pleasure
to try answering.

 

[Labguy]

Originally posted by marcus
Yeah, I know.
They are tricky objects.

Anyway we must not forget that it is now Labguys turn!

He will undoubtably pose us a question that will be a pleasure
to try answering.

I think you are over-rating my abilities.... No, the answer to this question will be either very easy, or very difficult to find, rather balck or white.

Question:
Galaxy 3C 66B is a galaxy with huge radio (and other EM) jets shooting out to very large distances. What other recent information, gathered/noticed, about this galaxy shows that it has a property that has been theorized, but not before seen (evidenced) by observations??

 

[marcus]

a binary pair of supermassive black holes
orbiting around each other
probably the result of the merger of two galaxies
each of which brought a central black hole with it

 

[marcus]

Originally posted by marcus
a binary pair of supermassive black holes
orbiting around each other
probably the result of the merger of two galaxies
each of which brought a central black hole with it

I forgot to tell the recent observation!

The braided jet.

The smaller of the two is emitting a jet----the way black holes do, from the stuff spiraling in and getting hot on the way and getting sent out along the axis---the obersevers think it is the smaller one making this long bright finger of a jet.

And because of the periodic (about 1 year period) going around there is a kind of CORKSCREW twisted braided look to the jet--nice looking like a unicorn's horn is sometimes shown on medieval tapestry, or a knobbly icicle.

http://www.astronomy.com/Content/Dynamic/Articles/000/000/001/338cudnh.asp

 

[marcus]

the telltale observation: short period motion

another telling observation
was "elliptical motion"
in the core of the galaxy

it was so short-period (one year)
that what else could it be?

to orbit each other so fast these extremely massive
things would have to be very close together
so most likely two black holes

probably the observers detected a doppler wobble
which plotted not sinusoidally but in a distorted
sinewave that means ellipse

this is cool, let us give it the guy with sunglasses

 

[Labguy]

That's it.

Your go.

 

[marcus]

Originally posted by Labguy
That's it.

Your go.

Early in the 17th century Kepler discovered that
one thing was "the sesquipotence" of another thing.

That was how he expressed it---i've taken a look at the
original Latin text with a literal translation. We say it
differently now, most likely, but he said "sesquipotence".

What did he mean by sesquipotence?
What were the two quantities he was talking about?
Which one was the sesquipotence of the other?
What year was this?----discovery and publication happend
within a few months of each other.

 

[marcus]

A different question, instead of the Kepler one

No one has replied so I will assume its not a good question and ask a different one.

New Question

What z corresponds to a light travel time of 12 billion years?

Assume spatial flatness.


http://www.astro.ucla.edu/~wright/CosmoCalc.html

This requires trying various z until you hit one that gives 12 billion years for the light travel time. When you type in a value for z, press the "flat" button and it will find the light travel time which corresponds to that z.

Unless you explicitly change the default settings, the calculator will assume H₀ is 71 in the usual units (km/s per Mpc) and Ω_vac = 0.73, and 0.27 for Ω_M = 0.27. These are widely accepted values so what I'm looking for is the answer with these default values for H₀, Ω_vac, and Ω_M left unchanged.


The Kepler question seems to have been too obscure So I withdraw it. For anyone who might be interested, here's a hint:
"sesquicentennial" means the "one-and-a-half century" mark. Sesqui is Latin for 1.5.

Originally posted by marcus
Early in the 17th century Kepler discovered that
one thing was "the sesquipotence" of another thing.

That was how he expressed it---i've taken a look at the
original Latin text with a literal translation. We say it
differently now, most likely, but he said "sesquipotence".

What did he mean by sesquipotence?
What were the two quantities he was talking about?
Which one was the sesquipotence of the other?
What year was this?----discovery and publication happend
within a few months of each other.

 

[Labguy]

z = 3.808

 

[marcus]

Originally posted by Labguy
z = 3.808

Beautiful! right on the button.

with z = 3.808 the light travel time comes out 12.000 billion years



also, as you probably saw, the current distance to an object whose past light is observed with redshift 3.808 is
given by the calculator as 23.362 billion light years.
this is the Hubble law distance D, so the present speed of
recession is 1.7 c.
We will never see that object as it is today (as long as expansion continues) because it is already out of range.
Nevertheless it and the many other redshift 3.8 objects in the sky are considered to belong to the observable universe, obviously, because we observe them. A paradox one must live with.

Your turn, Labguy. Ask a good one!

 

[Labguy]

Ok, but then I will (try) to sit out awhile to get some other players into this game. I think it is fun, but not everyone has the time to find answers or even look up a good question. I say try because sometimes it is so tempting to jump right on an easy one, or one that I happen, by chance, to already know. That's not many..

Question:
In the final stages of an implosion supernova, with enough energy to make the "heavy" elements to Lead and above (after the BOOM:

(1) Name the supernova type.
(2) Name the progenitor star type.
(3) Name the final two or three fusion-stages, by elements fused, that result in the last element produced before the implosion.
(4) Name the last element formed before the implosion.

This is not a trick question, but "elements" mean simply those as shown and named on any common periodic table, including any isotope of them, if applicable.

(Note: Marcus: Wait at least 4-5 minutes before answering.. ..)

 

[marcus]

Originally posted by Labguy
Ok, but then I will (try) to sit out awhile to get some other players into this game.implosion.
(Note: Marcus: Wait at least 4-5 minutes before answering.. ..)

OK Labguy I see your reason for sitting out a few. Maybe I will take a breather too. But we had some good questions going and I enjoyed it.

 

[Labguy]

Originally posted by marcus
OK Labguy I see your reason for sitting out a few. Maybe I will take a breather too. But we had some good questions going and I enjoyed it.

No, no. Go ahead on this one (anyone); it has been more than 30 minutes. This question seems simple, and can be, but I bet a lot of posters here would miss one item in particular.

HINT: Some of the "burning shell" graphics on pages discussed earlier might show an answer; but might not...

 

[marcus]

Originally posted by Labguy
No, no. Go ahead on this one (anyone); it has been more than 30 minutes. This question seems simple, and can be, but I bet a lot of posters here would miss one item in particular.

HINT: Some of the "burning shell" graphics on pages discussed earlier might show an answer; but might not...

well I am of two minds about this. I really enjoy this game as a friendly tennis match between the two of us because you know a lot of interesting stuff

on the other hand morally I think it would be good to be more inclusive---so that I should hold back and wait a while before answering each of your questions

I will compromise for now. I will answer ONE PART of your question and then whoever steps in and answers the rest can have a turn.

Let me know if I'm wrong about this----the last element to be made prior to collapse is IRON.

that would, I guess, have to be made from silicon which merges to nickel which emits two betas and decays to iron. I am just
speculating based on the numbers on the atomic table of elements.

 

[Labguy]

Originally posted by marcus
well I am of two minds about this. I really enjoy this game as a friendly tennis match between the two of us because you know a lot of interesting stuff

on the other hand morally I think it would be good to be more inclusive---so that I should hold back and wait a while before answering each of your questions

I will compromise for now. I will answer ONE PART of your question and then whoever steps in and answers the rest can have a turn.

Let me know if I'm wrong about this----the last element to be made prior to collapse is IRON.

that would, I guess, have to be made from silicon which merges to nickel which emits two betas and decays to iron. I am just
speculating based on the numbers on the atomic table of elements.

That was the only "hard" part. Most books, and internet sites just say silicon to Iron, when actually it is silicon to ⁵⁶NI and then to ⁵⁶Fe.

Anyone else who lists out the other answers will be the next question winner.

 

[Labguy]

Finish the other points on that question, Marcus. (or anyone)!

 

[chroot]

a) a Supernova Type II
b) a massive red supergiant

- Warren

 

[marcus]

Originally posted by Labguy


Question:
In the final stages of an implosion supernova, with enough energy to make the "heavy" elements to Lead and above (after the BOOM:

(1) Name the supernova type.
(2) Name the progenitor star type.
(3) Name the final two or three fusion-stages, by elements fused, that result in the last element produced before the implosion.
(4) Name the last element formed before the implosion.

The progenitor star would be a red giant, of some initially very massive class like a spectral type O.

The supernova is type II-----the implosion kind as opposed to Type Ia, the thermonuclear kind.

As we already discussed the last element is iron
which results from decay of nickel and cobalt.

The last fusion stage is silicon to nickel.

I don't remember just how many solar masses the original star has to be in order to be able to make Type II---or even how positive astrophysicists are about that. So I just say very massive, like a spectral type O or thereabouts. Is that right?

 

[chroot]

We currently don't know the requisite masses for a star to become a Type II SN. We do know that the iron core of the star has to be larger than the Chandrasekhar "limit," but we're not sure how much mass is lost from the envelope in the explosion, and thus are not sure about the star's minimal total mass.

Neener neener boo boo -- I beat you by seconds. :)

- Warren

 

[Labguy]

Originally posted by chroot
We currently don't know the requisite masses for a star to become a Type II SN. We do know that the iron core of the star has to be larger than the Chandrasekhar "limit," but we're not sure how much mass is lost from the envelope in the explosion, and thus are not sure about the star's minimal total mass.

Neener neener boo boo -- I beat you by seconds. :)

- Warren

Yes, you "finished the list" within seconds of that "other guy".

chroot ask next question.

 

[Labguy]

Somebody ask another question. I survived the surgery I had yesterday and can sit at my desk again without pain pills...

 

[marcus]

Originally posted by Labguy
Somebody ask another question. I survived the surgery I had yesterday and can sit at my desk again without pain pills...

That's good news. Congratulations! How's the weather in Tampa Bay area----beautiful around SF Bay now and not too hot.
The universe is expanding. It is Chroot's turn.

 

[Shadow]

I know that I have never posted in this thread but it seems to me that it will be a while before chroot comes back from wherever he may be. It has been 7 days since his last post in this thread so perhaps someone else should go or maybe they could simply send a private message to Chroot.

 

[Labguy]

Originally posted by Shadow
I know that I have never posted in this thread but it seems to me that it will be a while before chroot comes back from wherever he may be. It has been 7 days since his last post in this thread so perhaps someone else should go or maybe they could simply send a private message to Chroot.

No, I asked the last question, but enough time has gone by for chroot to answer with his question since he got the last one right.

If Shadow is "new" around here, take it and ask away. Otherwise, anyone can jump in now. I think that summer vacations will lose some of the regulars for awhile.

 

[marcus]

Originally posted by Labguy
No, I asked the last question, but enough time has gone by for chroot to answer with his question since he got the last one right.

If Shadow is "new" around here, take it and ask away. Otherwise, anyone can jump in now. I think that summer vacations will lose some of the regulars for awhile.

I will jump in. My excuse is that I answered almost all of the last question but Chroot beat me to the punch on the final part.

---------------------------------

Use this to answer a simple question:

http://www.astro.ucla.edu/~wright/CosmoCalc.html

How long, before the present, has it taken the universe to expand by a factor of two?

To rephrase that, how long ago were distant galaxies, that are like 1 billion LY away now, just half as far away?

--------------------------

This assumes the current assumptions cosmologists make----namely Hubble parameter 71, spatial flatness, cosmological constant 73 percent. But that is all built into the CosmoCalculator.
You just have to plug in a value of the redshift z and it will tell you how long.

But be sure to plug in the value of z that goes with the idea of expanding by a factor of two!

 

[Shadow]

I'm sorry I have never used a website like that before. I usually post in the philosophy and political forums and I am an "ameteur" astronomer. I have a telescope and a few books on astronomy that I read in spare time but I have not gotten very far yet so I am hoping to learn by this thread.


-Shadow

 

[marcus]

Originally posted by Shadow
I'm sorry I have never used a website like that before. I usually post in the philosophy and political forums and I am an "ameteur" astronomer. I have a telescope and a few books on astronomy that I read in spare time but I have not gotten very far yet so I am hoping to learn by this thread.

Shadow would you mind if I talked you thru this? then you would get the answer and the next turn to ask would be yours.

If you would not mind the bother of just mechanically going thru the motions (if you do, say no!) then here it is.

There is only one thing to do.
Go to

*************

http://www.astro.ucla.edu/~wright/CosmoCalc.html

And plug the number 1 into the box that says "z"

It is over on the left side

And then click on the box that says "Flat"

that will do it.

The number of years will show up in the "light travel time" box
on the right of the screen.

Be sure to put the number ONE into the "z" box, and press "Flat".
dont change any of the other settings cause they are usually right. If you have any trouble, post here or write me a PM and I will help.

******the question, quoted from previous post*******

How long, before the present, has it taken the universe to expand by a factor of two?

To rephrase that, how long ago were distant galaxies, that are like 1 billion LY away now, just half as far away?


This assumes the current assumptions cosmologists make----namely Hubble parameter 71, spatial flatness, cosmological constant 73 percent. But that is all built into the CosmoCalculator.
You just have to plug in a value of the redshift z and it will tell you how long.

But be sure to plug in the value of z that goes with the idea of expanding by a factor of two!

FOOTNOTE: the expansion factor corresponding to redshift z is 1+z

So the expansion factor corresponding to redshift 1 is 1+1 =2
But that's what the question is about! Expansion by a factor of two! So the z to use is z = 1.

If you want to know how long it took for the universe to triple---i.e. expand three-fold---up to the present, then put z = 2 into Ned Wright's calculator. Always put one less than the expansion factor you want to know about. There's nothing wrong it is just how astro conventions work and how the calculator is constructed.