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Gaia Spectrum Data


Someone posted on May 12 a link to the American Museum Natural History Sci Cafe's visualizations of Gaia data.
This video presents star positions (I assumed based on luminosity) and relative velocities (I assume based on shifts in absorption lines) of a subset of stars in the Milky Way.

I have several comments about this Gaia data.

With Robitaille and Crothers working on luminosity curves I wonder if mistakes are being made on stellar distances.

First, controversial stars.

1) Black holes

According to a National Geographic story :
'
the study authors think that as many as 500 black hole binaries exist in the Milky Way, and that the galaxy hosts up to ten thousand black holes in total.'

Did Gaia capture any of them?

I doubt it, but that description will be interesting. A black hole is bright source of electromagnetic radiation with no visual object, sometimes with jets, but a  source in electromagnetic effects is not considered.

2) Neutron stars

According to NASA's Fermi Gamma-ray Space Telescope Mission News:

'
Astronomers have found less than 2,000 pulsars, yet there should be about a billion neutron stars in our Milky Way Galaxy. There are two reasons for this shortfall. One is age: most neutron stars are billions of years old, which means they have plenty of time to cool and spin down.
'

Did Gaia capture any of them?

I doubt it, but that description will be interesting. A neutron star is typically a pulsar where the cause of the frequency of oscillating radiation is actually electrical not rotational. There are some non-pulsating neutron stars.

Other general comments.

3) Reliability of calculated relative velocities

I had posted on May 15 about possible problems interpreting absorption lines and emission lines.
 
With the release of Gaia data so recently I wonder if efforts like by AMNH are premature before  the data has been properly filtered.

I have these observations for Gaia interpretations:

A) The density of neutral hydrogen in interstellar space could affect shifts in hydrogen absorption lines. Analysis of these red shifts among many stars might define the locations of those clouds, but only if not taken as a star's velocity.

B) The interstellar medium probably affects this data.

from Wikipedia:

'
The interstellar medium is composed of multiple phases, distinguished by whether matter is ionic, atomic, or molecular, and the temperature and density of the matter. The interstellar medium is composed primarily of hydrogen followed by helium with trace amounts of carbon, oxygen, and nitrogen comparatively to hydrogen. The thermal pressures of these phases are in rough equilibrium with one another. Magnetic fields and turbulent motions also provide pressure in the ISM, and are typically more important dynamically than the thermal pressure is.
'

When I read 'thermal' and 'turbulent' I read that as atoms in motion and possibly ionized. These ions could provide shifted emission lines.

C)
Interstellar Clouds

from Wikipedia:

'An interstellar cloud is generally an accumulation of gas, plasma, and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium, (ISM), the matter and radiation that exists in the space between the star systems in a galaxy. Depending on the density, size, and temperature of a given cloud, its hydrogen can be neutral, making an H I region; ionized, or plasma making it an H II region; or molecular, which are referred to simply as molecular clouds, or sometimetimes dense clouds. Neutral and ionized clouds are sometimes also called diffuse clouds. An interstellar cloud is formed by the gas and dust particles from a red giant in its later life.
'

D) Binary stars

According to a University of Oregon study:

'
 In fact, 85% of the stars in the Milky Way galaxy are not single stars, like the Sun, but multiple star systems, binaries or triplets.'


I assume these combinations of stars, probably not always the same mass, complicate the observed emission line shifts. The stars are in motion around each other but the orbital duration must be considered to determine the motion of the pair relative to Earth.

Perhaps nearby ions in motion, separate from the star's motion like in a solar wind passing between the stars, are detected by Gaia for the individual stars.

Also these stars, both by their presence and their motion, probably affect the motion within the interstellar medium. I expect at a minimum they would affect the density of interstellar neutral hydrogen just as a distant gravitational field, though perhaps weak relative to the intergalactic magnetic field which could hinder a free fall behavior of ions within the medium.

4)
As with my posts about claimed galactic motions, I must be skeptical about claimed stellar motions.
Will mistakes be repeated?


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