Any PhD astrophysicists on board?

[SLD]

Just wondering.

 

[lpetrich]

Just wondering.

I am. What do you wish to ask about?

 

[skepticalbip]

Just wondering.

I am. What do you wish to ask about?

..How is the bar structure in a barred spiral galaxy maintained?
..What is it that makes up the gravitational anomaly, "the great attractor"?
..Is Penrose's conformal cyclic cosmology (CCC) model taken seriously by anyone other than mathematicians?

 

[Loren Pechtel]

If you pile stars higher and deeper I would think you would end up pretty squashed.

 

[fromderinside]

Critique or observation?

 

[lpetrich]

..How is the bar structure in a barred spiral galaxy maintained?

NASA - Barred Spiral Galaxies Are Latecomers to the Universe

A team led by Kartik Sheth of the Spitzer Science Center at the California Institute of Technology in Pasadena discovered that only 20 percent of the spiral galaxies in the distant past possessed bars, compared with nearly 70 percent of their modern counterparts.

Bars have been forming steadily over the last 7 billion years, more than tripling in number. "The recently forming bars are not uniformly distributed across galaxy masses, however, and this is a key finding from our investigation," Sheth explained. "They are forming mostly in the small, low-mass galaxies, whereas among the most massive galaxies, the fraction of bars was the same in the past as it is today."

The findings, Sheth continued, have important ramifications for galaxy evolution. "We know that evolution is generally faster for more massive galaxies: They form their stars early and fast and then fade into red disks. Low-mass galaxies are known to form stars at a slower pace, but now we see that they also made their bars slowly over time," he said.

...
Bars form when stellar orbits in a spiral galaxy become unstable and deviate from a circular path. "The tiny elongations in the stars' orbits grow and they get locked into place, making a bar," explained team member Bruce Elmegreen of IBM's research Division in Yorktown Heights, N.Y. "The bar becomes even stronger as it locks more and more of these elongated orbits into place. Eventually a high fraction of the stars in the galaxy's inner region join the bar."

Added team member Lia Athanassoula of the Laboratoire d'Astrophysique de Marseille in France: "The new observations suggest that the instability is faster in more massive galaxies, perhaps because their inner disks are denser and their gravity is stronger."

..What is it that makes up the gravitational anomaly, "the great attractor"?

Explainer: What is the Great Attractor and its pull on the Milky Way? -- not sure yet. A supercluster of galaxies? A concentration of dark matter without galaxies?

..Is Penrose's conformal cyclic cosmology (CCC) model taken seriously by anyone other than mathematicians?

 Conformal cyclic cosmology - "In CCC, the universe iterates through infinite cycles, with the future timelike infinity of each previous iteration being identified with the Big Bang singularity of the next."

Penrose's basic construction[5] is to connect a countable sequence of open Friedmann–Lemaître–Robertson–Walker metric (FLRW) spacetimes, each representing a Big Bang followed by an infinite future expansion. Penrose noticed that the past conformal boundary of one copy of FLRW spacetime can be "attached" to the future conformal boundary of another, after an appropriate conformal rescaling. In particular, each individual FLRW metric g_ab is multiplied by the square of a conformal factor Ω that approaches zero at timelike infinity, effectively "squashing down" the future conformal boundary to a conformally regular hypersurface (which is spacelike if there is a positive cosmological constant, as is currently believed). The result is a new solution to Einstein's equations, which Penrose takes to represent the entire universe, and which is composed of a sequence of sectors that Penrose calls "aeons".

I then went to Google Scholar to see how much has been written on it. For "conformal cyclic cosmology" I found 302 hits, while for "multiverse" I found 25,700 hits.

 

[Shadowy Man]

Just wondering.

Yes.

 

[skepticalbip]

NASA - Barred Spiral Galaxies Are Latecomers to the Universe

..What is it that makes up the gravitational anomaly, "the great attractor"?

Explainer: What is the Great Attractor and its pull on the Milky Way? -- not sure yet. A supercluster of galaxies? A concentration of dark matter without galaxies?

..Is Penrose's conformal cyclic cosmology (CCC) model taken seriously by anyone other than mathematicians?

 Conformal cyclic cosmology - "In CCC, the universe iterates through infinite cycles, with the future timelike infinity of each previous iteration being identified with the Big Bang singularity of the next."

Penrose's basic construction[5] is to connect a countable sequence of open Friedmann–Lemaître–Robertson–Walker metric (FLRW) spacetimes, each representing a Big Bang followed by an infinite future expansion. Penrose noticed that the past conformal boundary of one copy of FLRW spacetime can be "attached" to the future conformal boundary of another, after an appropriate conformal rescaling. In particular, each individual FLRW metric g_ab is multiplied by the square of a conformal factor Ω that approaches zero at timelike infinity, effectively "squashing down" the future conformal boundary to a conformally regular hypersurface (which is spacelike if there is a positive cosmological constant, as is currently believed). The result is a new solution to Einstein's equations, which Penrose takes to represent the entire universe, and which is composed of a sequence of sectors that Penrose calls "aeons".

I then went to Google Scholar to see how much has been written on it. For "conformal cyclic cosmology" I found 302 hits, while for "multiverse" I found 25,700 hits.

Thanks. Interesting but it didn't answer the questions. I understood the above which is what raised the questions.

.. The stars in the bar are "locked" into the bar. How are they "locked"?

.. For the "great attractor", I thought that you, as a PHD astrophysicist may have a favorite and reasonable hypothesis as to what was creating that gravitational anomaly.

... I understood the Penrose CCC involved successive rescalings of the space-time mapping. This, to me, is a mathematical 'trick' analogous to plotting an exponential growth of a function on a semi-log scale so several orders of magnitude increase can be displayed on the same graph. The question was if any of your astrophysicist associates take it seriously as representing an actual physical cycling of the universe or if it is only, for lack of a better term, astromathemicians that take it seriously.

 

[lpetrich]

.. The stars in the bar are "locked" into the bar. How are they "locked"?

By their gravity.

.. For the "great attractor", I thought that you, as a PHD astrophysicist may have a favorite and reasonable hypothesis as to what was creating that gravitational anomaly.

The Great Attractor is close to the plane of our Galaxy, and that makes it hard to observe what's in it. One has to observe in infrared and radio.

... I understood the Penrose CCC involved successive rescalings of the space-time mapping. This, to me, is a mathematical 'trick' analogous to plotting an exponential growth of a function on a semi-log scale so several orders of magnitude increase can be displayed on the same graph. The question was if any of your astrophysicist associates take it seriously as representing an actual physical cycling of the universe or if it is only, for lack of a better term, astromathemicians that take it seriously.

The Wikipedia article on it discusses some possible experimental tests of it, though it looks to me as hard to test as multiverse hypotheses.

I'd like to see some examples of your distinction between astrophysics and astromathematics, so I can understand your distinction better.

 

[Shadowy Man]

The question was if any of your astrophysicist associates take it seriously as representing an actual physical cycling of the universe or if it is only, for lack of a better term, astromathemicians that take it seriously.

That distinction doesn't exist. I think you are meaning "theoretical astrophysicist" by the latter term.

 

[Loren Pechtel]

If you pile stars higher and deeper I would think you would end up pretty squashed.

Critique or observation?

Are you aware of what I was referring to with piled higher and deeper? I was picturing stars piled higher and deeper.

 

[DBT]

I don't get why one of a pair of virtual particles escaping would causes a black hole to evaporate given that virtual pairs form outside of the event horizon in the first instance.

 

[barbos]

I don't get why one of a pair of virtual particles escaping would causes a black hole to evaporate given that virtual pairs form outside of the event horizon in the first instance.

The particle which gets eaten by the black hole have negative energy, hence total energy (mass) of the black hole gets smaller.

 

[DBT]

I don't get why one of a pair of virtual particles escaping would causes a black hole to evaporate given that virtual pairs form outside of the event horizon in the first instance.

The particle which gets eaten by the black hole have negative energy, hence total energy (mass) of the black hole gets smaller.

But how do we know that the laws/principles of physics apply to a singularity? Doesn't that break down?

 

[barbos]

I don't get why one of a pair of virtual particles escaping would causes a black hole to evaporate given that virtual pairs form outside of the event horizon in the first instance.

The particle which gets eaten by the black hole have negative energy, hence total energy (mass) of the black hole gets smaller.

But how do we know that the laws/principles of physics apply to a singularity? Doesn't that break down?

Well, theory is incomplete but it is as self-consistent as we can do right now.

 

[SLD]

Just wondering.

I am. What do you wish to ask about?

What area of research?

 

[SLD]

Just wondering.

Yes.

And what area do you research?

 

[Shadowy Man]

Just wondering.

Yes.

And what area do you research?

I am no longer active in the field of astrophysics but I studied dust, atoms and molecules in the interstellar medium and developed astronomical instrumentation.