Starship Asterisk*

john_erickson wrote:

jonas s wrote:The quoted spin rate as a linear velocity, km/sec. What is the angular rate of spin or is the quoted km/sec at baseline distance from center of rotation?

jonas s wrote:The quoted spin rate as a linear velocity, km/sec. What is the angular rate of spin or is the quoted km/sec at baseline distance from center of rotation?

MartinNi wrote:

neufer wrote:

Bopps wrote:
The orbits of earth satellites are at altitudes defined by their velocity ... higher velocity to maintain higher altitudes. As their velocity decays they eventually fall back to earth. If galaxy objects are at the same linear velocity, they would be "falling" towards the center. Does this explain arms spiraling inward towards the center black hole of galaxies?

The (~circular) orbits of earth satellites are at altitudes defined by their velocity
... higher velocities are needed to maintain lower altitudes:

Centrifugal force = mv²/r = gravitational force = GmM/r²

Hence: v² = GM/r : or v = sqrt (GM/r)

For (~circular) orbital velocity to be constant
the gravitational force of galaxies must drop off more slowly as 1/r not 1/r².

Centrifugal force = mv²/r = gravitational force = Cm/r (; i.e., total dark mass M grows as Cr/G)

Hence: v² = C : or v = sqrt (C)

(; i.e., UGC 12591's dark mass density is ~4 times that of the Milky Way.)

Hi Art, isn't this simple formalism for point masses (or masses with radial symmetric distibution, when located "outsite" of them) rather inadequate (and so the estimated "dark mass density" wrong) for a much more non-spherical mass distribution, which a flat disk like UGC 12591 represents ?

What about a correct formalism for spiral galaxies ?

neufer wrote:

Bopps wrote:
The orbits of earth satellites are at altitudes defined by their velocity ... higher velocity to maintain higher altitudes. As their velocity decays they eventually fall back to earth. If galaxy objects are at the same linear velocity, they would be "falling" towards the center. Does this explain arms spiraling inward towards the center black hole of galaxies?

The (~circular) orbits of earth satellites are at altitudes defined by their velocity
... higher velocities are needed to maintain lower altitudes:

Centrifugal force = mv²/r = gravitational force = GmM/r²

Hence: v² = GM/r : or v = sqrt (GM/r)

For (~circular) orbital velocity to be constant
the gravitational force of galaxies must drop off more slowly as 1/r not 1/r².

Centrifugal force = mv²/r = gravitational force = Cm/r (; i.e., total dark mass M grows as Cr/G)

Hence: v² = C : or v = sqrt (C)

(; i.e., UGC 12591's dark mass density is ~4 times that of the Milky Way.)

Charles J. Peterson (a relative, Chris?) wrote in Astronomical Journal, vol. 85, Mar. 1980, p. 226-229:

The rotation curve of NGC 488 has been measured out to a radius of 20 kpc, at which point the velocity is 363 km⁻¹ and continuing to increase with radius. This rotational velocity is the largest known for an Sb galaxy. For a mass model based on the thin-disk approximation of Kuzmin [Publ. Tartu Astron. Obs. 32, 211 (1952)], we find the mass and mass-luminosity interior to 20 kpc are M ⪆ 4.0 X 10¹¹ M_☉ and <M/L>_B ⪆ 3.6. Exterior to the nuclear region, the mass-luminosity relation shows only a gentle increase with radius.

Chris Peterson wrote:

pipejazz wrote:
Numerous galaxies, is this gravational lensing or reality?

Gravitational lensing is reality! But I don't see any obvious lensing in this image. (And the object in this image is much too close to be an effective lens.)

RJN wrote:

Rajesh Kalmady wrote:The light from the galaxy left 400 million years ago, not 400 million light years ago.

Oops! Yes. Fixed it on the main NASA APOD. Thanks!

- RJN

https://en.wikipedia.org/wiki/ISOHDFS_27 wrote:

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<<ISOHDFS 27 is the most massive spiral galaxy in the Hubble Deep Field South known so far which is 130,000 light-years in diameter. It is approximately 6 billion light years from Earth. It has a mass of 1.04×10¹² solar masses (M_☉), about four times as massive as the Milky Way.

The preceding most massive spiral was UGC 12591.>>

https://en.wikipedia.org/wiki/Segue_2 wrote:

[b][color=#0000FF]The galaxy Segue 2: boxes are ten member stars identified so far by University of California Irvine astronomers and their colleagues (Sci-News.com / Centre de Données astronomiques de Strasbourg / SIMBAD)[/color][/b]

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<<Segue 2 is a dwarf spheroidal galaxy situated in the constellation Aries and discovered in 2009 in the data obtained by Sloan Digital Sky Survey. The galaxy is located at the distance of about 35 kpc (110,000 ly) from the Sun and moves towards the Sun with the speed of 40 km/s. It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an approximately round shape with the half-light radius of about 34 pc. Segue 2 is located near the edge of Sagittarius Stream and at the same distance. It may once have been a satellite of Sagittarius Dwarf Elliptical Galaxy or its star cluster.

Segue 2 is one of the smallest and faintest satellites of the Milky Way—its integrated luminosity is about 800 times that of the Sun (absolute visible magnitude of about −2.5), which is much lower than the luminosity of the majority of globular clusters. Circa 1,000 stars are supposed to exist within the galaxy. However, the mass of the galaxy—about 550,000 solar masses—is substantial, corresponding to the mass to light ratio of about 650. In June 2013 the The Astrophysical Journal reported that Segue 2 was bound together with dark matter.

The stellar population of Segue 2 consists mainly of old stars formed more than 12 billion years ago. The metallicity of these old stars is also very low at [Fe/H] < −2, which means that they contain at least 100 times less heavy elements than the Sun. The stars of Segue 2 were probably among the first stars to form in the Universe. Currently, there is no star formation in Segue 2.>>

RJN wrote:

Rajesh Kalmady wrote:
The light from the galaxy left 400 million years ago, not 400 million light years ago.

Oops! Yes. Fixed it on the main NASA APOD. Thanks!

https://en.wikipedia.org/wiki/Tree#Evolutionary_history wrote:

[b][color=#0000FF]Barack Obama interviewed on Between Two Ferns with Zach Galifianakis, 2014[/color][/b]

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<<The earliest tree-like organisms were tree ferns, horsetails and lycophytes, which grew in forests in the Carboniferous period. The first tree may have been Wattieza, fossils of which have been found in New York State in 2007 dating back to the Middle Devonian (about 385 million years ago). Prior to this discovery, Archaeopteris was the earliest known tree. Both of these reproduced by spores rather than seeds and are considered to be links between ferns and the gymnosperms which evolved in the Triassic period. The gymnosperms include conifers, cycads, gnetales and ginkgos and these may have appeared as a result of a whole genome duplication event which took place about 319 million years ago. Ginkgophyta was once a widespread diverse group of which the only survivor is the maidenhair tree Ginkgo biloba. This is considered to be a living fossil because it is virtually unchanged from the fossilised specimens found in Triassic deposits.

During the Mesozoic (245 to 66 million years ago) the conifers flourished and became adapted to live in all the major terrestrial habitats. Subsequently, the tree forms of flowering plants evolved during the Cretaceous period. These began to dominate the conifers during the Tertiary era (66 to 2 million years ago) when forests covered the globe. When the climate cooled 1.5 million years ago and the first of four ice ages occurred, the forests retreated as the ice advanced. In the interglacials, trees recolonised the land that had been covered by ice, only to be driven back again in the next ice age.>>

Rajesh Kalmady wrote:The light from the galaxy left 400 million years ago, not 400 million light years ago.

pipejazz wrote:Numerous galaxies, is this gravational lensing or reality? :D

De58te wrote:In the expanded view next to the galaxy pointed out by Coil Smoke, there are two neat blue galaxies really close to each other. I wonder if they are colliding?
Also look at the neat all red galaxy just above the ESA letters. I wonder why the galaxy is all red. Could it be due to the expansion of the universe and all the distant galaxies are red shifted because they are moving away from us? There are about 2 or 3 other red galaxies along the bottom, but through the rest of the photograph the galaxies are either white or blue. There are a lot of blue distant galaxies visible. Would those galaxies be blue shifted because they are all moving towards us? That would be at odds with the distant galaxies being red shifted.

De58te wrote:In the expanded view next to the galaxy pointed out by Coil Smoke, there are two neat blue galaxies really close to each other. I wonder if they are colliding?
Also look at the neat all red galaxy just above the ESA letters. I wonder why the galaxy is all red. Could it be due to the expansion of the universe and all the distant galaxies are red shifted because they are moving away from us? There are about 2 or 3 other red galaxies along the bottom, but through the rest of the photograph the galaxies are either white or blue. There are a lot of blue distant galaxies visible. Would those galaxies be blue shifted because they are all moving towards us? That would be at odds with the distant galaxies being red shifted.

Bopps wrote:
The orbits of earth satellites are at altitudes defined by their velocity ... higher velocity to maintain higher altitudes. As their velocity decays they eventually fall back to earth. If galaxy objects are at the same linear velocity, they would be "falling" towards the center. Does this explain arms spiraling inward towards the center black hole of galaxies?