APOD: Gaia's Milky Way (2018 Apr 27)

Comments and questions about the APOD on the main view screen.
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neufer
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Re: APOD: Gaia's Milky Way (2018 Apr 27)

Post by neufer » Sun Apr 29, 2018 4:57 pm

Ann wrote:
Sun Apr 29, 2018 5:16 am

So the way to understand Gaia's ability to detect M33 and its inability(?) to detect M31 is to realize that Gaia can't photograph a galaxy "all at once", but only "star by star" or "discrete light source by discrete light source". And M31 has too few sufficiently bright discrete light sources in order to show up clearly in Gaia's picture.
https://en.wikipedia.org/wiki/Triangulum_Galaxy wrote:
<<Star formation is taking place at a rate that is strongly correlated with the local gas density, and the rate per unit area is higher than in the neighboring Andromeda Galaxy. (The rate of star formation is about 3.40 Gyr−1 pc−2 in the Triangulum galaxy, compared to 0.74 in Andromeda.)>>
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Re: APOD: Gaia's Milky Way (2018 Apr 27)

Post by neufer » Thu May 03, 2018 2:59 am

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Re: APOD: Gaia's Milky Way (2018 Apr 27)

Post by Fred the Cat » Sat Oct 09, 2021 1:41 pm

The Milky Way galaxy resides in an area of relatively nothing. :| We investigate physics on Earth but, “Do we live in the best part of the universe to test theories?” Could physics even be tested?

Dark energy theory's themselves could rest in the balance. :thumb_up:
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Re: APOD: Gaia's Milky Way (2018 Apr 27)

Post by Chris Peterson » Sat Oct 09, 2021 1:49 pm

Fred the Cat wrote:
Sat Oct 09, 2021 1:41 pm
The Milky Way galaxy resides in an area of relatively nothing. :| We investigate physics on Earth but, “Do we live in the best part of the universe to test theories?” Could physics even be tested?

Dark energy theory's themselves could rest in the balance. :thumb_up:
There are many, many measurements that we make of things in distant parts of the Universe, all of which offer powerful evidence that the rules of physics we observe here are the same everywhere.
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Re: APOD: Gaia's Milky Way (2018 Apr 27)

Post by Fred the Cat » Sat Oct 09, 2021 2:40 pm

Chris Peterson wrote:
Sat Oct 09, 2021 1:49 pm
Fred the Cat wrote:
Sat Oct 09, 2021 1:41 pm
The Milky Way galaxy resides in an area of relatively nothing. :| We investigate physics on Earth but, “Do we live in the best part of the universe to test theories?” Could physics even be tested?

Dark energy theory's themselves could rest in the balance. :thumb_up:
There are many, many measurements that we make of things in distant parts of the Universe, all of which offer powerful evidence that the rules of physics we observe here are the same everywhere.
I can only question things from a basic understanding of physics and an interest to know more. When you read lay info, written by physicists, that are questioning topics of the unknown variety, it stirs the curiosity and are fun to share. Like, " If gravitational waves flow along cosmic filaments or through voids or both? Maybe the string section will chime in? :wink:
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Re: APOD: Gaia's Milky Way (2018 Apr 27)

Post by alter-ego » Sun Oct 10, 2021 12:05 am

Fred the Cat wrote:
Sat Oct 09, 2021 2:40 pm
Chris Peterson wrote:
Sat Oct 09, 2021 1:49 pm
Fred the Cat wrote:
Sat Oct 09, 2021 1:41 pm
The Milky Way galaxy resides in an area of relatively nothing. :| We investigate physics on Earth but, “Do we live in the best part of the universe to test theories?” Could physics even be tested?

Dark energy theory's themselves could rest in the balance. :thumb_up:
There are many, many measurements that we make of things in distant parts of the Universe, all of which offer powerful evidence that the rules of physics we observe here are the same everywhere.
I can only question things from a basic understanding of physics and an interest to know more. When you read lay info, written by physicists, that are questioning topics of the unknown variety, it stirs the curiosity and are fun to share. Like, " If gravitational waves flow along cosmic filaments or through voids or both? Maybe the string section will chime in? :wink:
Interesting postulate.
Excluding regions of space within black-hole event horizons, a fundamental General Relativity principle is space-time is well defined everywhere within the Universe, and gravitational radiation propagates in all directions throughout "all" of space-time. Therefore, since you are constraining gravitational radiation within filaments, you're question implies space-time only exists within cosmic filaments. That also means that normal photons only travel within cosmic filaments. However, the fact cosmic filaments (and the voids) are mapped through observation, i.e. both voids and filaments are visible by the presence of, and lack of matter, space-time necessarily must exist in both voids and filaments.
This reasoning seems to be the simplest approach to convince oneself that space-time does not have voids between cosmic filaments.

Does space-time have voids? For discussion sake, if there are, they would not be visible with the electromagnetic spectrum, and I believe not visible with gravitational radiation. However, If / when gravitational radiation observatories are evolved as far as our present EM radiation observatories, we may discover new things and new questions about our Universe and its evolution.
A pessimist is nothing more than an experienced optimist