Stellar Aberration effects on the identification of rotation directions of spiral galaxies
Abstract
In this paper the well documented non-relativistic classical effects of stellar aberration (1) are applied to light arriving to the earth observer from external spiral galaxies with possible implications for spiral galaxy rotation direction identifications. It is proposed here in this paper that the range of rotational velocities of stars within any external galaxy(4) must exert a blurring effect on that galaxies total emitted light incident at any earth observers image plane. In that the different internal velocities of all the stars in a spiral galaxy that rotates in the same direction as our Milky Way should effect more blurring of the spiral galaxy at the earth observers image plane due to stellar aberration, than the blurring of light at the image plane will be for light coming from all the stars in a galaxy that rotates in the opposite direction to our Milky Way. This proposed non-relativistic classical effect of stellar aberration(1) could make it harder to identify a co rotating spiral galaxy’s rotation direction than it would for a counter rotating galaxy’s rotation direction at any similar redshift distance from earth.
Introduction
The basis for this papers’ proposed Stellar Aberration effect on light arriving from spiral galaxies is based on the assumption that if light from any stellar object is displaced at an observer’s image plane via stellar aberration (1) then the magnitude of that displacement will be dictated by the earth observer’s relative transverse velocity to that particular stellar source. The accepted rule for stellar aberration (1) being that a higher transverse velocity of a star relative to the earth observers will result in a larger displacement of the star at the observers’ image plane. And that the scale of any additional displacement with any subsequent additional increases in relative transverse velocities will always be observed to increase (1) by smaller displacement amounts at the image plane with any subsequent increases in relative transverse velocities between the source and observer. For example, using only the pre relativistic classical theory of stellar aberration (1), the difference in the lateral displacement of a stars position at the image plane due to a difference in relative transverse velocities of between 0 to 25km/s between source and observer is assumed here to be larger than the difference in displacement of a stars light with a relative transverse velocity difference between the source and observer of between 25-50km/s. As also illustrated below in Fig 1 & 2 and summarised as follows:
For an increase in differences of velocity v in relative transverse velocities between source and observer a displacement d at the observers’ image plane will be observed. For any additional velocity increase of velocity v in relative transverse velocity between source and observer the observed additional increase in displacement at the image plane will be <d
This paper then proposes here that this same classical stellar aberration effect noted for stars in the Milky Way (1) should also be visible in any light coming from any individual star within any observed external spiral galaxy. And thus, that this range in velocities of rotational motions of all the stars in any external spiral galaxy must also effect a visible range of displacements of light from the observed spiral Galaxy as its light arrives at the earth observers image plane.
Current estimates based on observations (2,3) of stellar rotational velocities around the Milky Way core are between 200 - 250km/s. Although rotational velocities may vary greatly across spiral galaxies this cited 200-250km/s velocity range (2,3) for stars in the Milky Way is assumed here for the purposes of this paper to be also an average rotational velocity range for all stars in all spiral galaxies. Thus, it is assumed here in this paper that the internal stellar rotational velocities in all galaxies
around their respective cores can be on average approximated to be in the range of around 200- 250km/s. And that it follows that the average range of stellar velocities around a spiral Galaxy core can be assumed to be approximately 50km/s between the slowest and the fastest stellar velocities. It should be noted here that this assumption is roughly in line with the published analysis of observed data of various spiral galaxy types (4). The conclusion based on this above cited data and reached here in this paper is that the average velocity range of all stars in any spiral Galaxy can be considered here for the purposes of this paper to be equivalent to up to 1/5 of the total average rotational velocity of its host spiral galaxy. This insinuates that all light coming from any spiral galaxy will have a range of transverse velocities relative to the earth observer of approximately 1/5 more or less than its average galactic rotational velocity.
It is important to point out here that although both the James Bradley classical and the later Relativistic theories of Stellar aberration predict similar displacements of light at the earth observers image plane (1). It is considered here for the purposes of this paper necessary only for one to invoke Bradley’s Classical theory of stellar aberration to fully explain not only the displacement of light but the predicted blurring of spiral Galaxies light at the earth observers image plane.
Displacement and blurring mechanism
Taking into account classical stellar aberration effects, it is proposed here in this paper that this assumed average velocity range of stars within galaxies (1,2,3,4) could have a significant measurable effect on light arriving from galaxies to the earth observer. In that the range of displacements from stellar aberration alone (1) at the image plane of light from any spiral galaxy should create an optical blurring of the galaxy at the earth observers image plane. And that it is predicted here in this paper that the images of spiral galaxies will more or less blurred depending on whether or not the observed spiral galaxy is rotating with or oppositely to our own Milky Way. To summarise, displacements of stellar positions within images of spiral galaxies due to the classical theory of stellar aberration will create a proposed range of blurring of spiral galaxies at the earth observers image plane that is straightforward and can be summarised as follows:
A) The relative transverse velocity between any stellar source and earth observer effects a lateral displacement of that light on the image plane due to stellar aberration (1). And that this displacement is then assumed here to occur to light from stars within our Milky Way and from stars located in any other external spiral galaxies.
B) The theory of stellar aberration based on centuries of observation (1) tells us that the higher the relative transverse velocity the greater the displacement at the image plane from stellar aberration will be. And also that any subsequent increase in relative velocity will create a subsequently smaller amount of further lateral displacement on the image plane. (Fig1&2)
C) It is assumed in this paper (3,4) that the average rotation velocity of spiral galaxies will be in a mid range of 225km/s.
D) Based on the above cited averages it assumed here that spiral galaxies rotating oppositely to our Milky Way will have internal stellar transverse rotation velocities of on average between 200- 250km/s relative to an earth observer, and that stars orbiting in spiral galaxies that are rotating with our Milky Way will have an internal transverse velocity range of approximately +-25km/s relative to the earth observer. Both ranges being on average consisting of a velocity difference of 50km/s.
E) Lateral displacements at the image plane due to Stellar aberration always are observed to increase with increases in relative velocities between source and observer (1). But successive lateral displacements increase less so in magnitude between successively larger increases in relative velocities between source and observer (1). As also illustrated in Fig 1 & 2 below.
With all these points taken into consideration it becomes obvious, particularly from point E) above, that the total difference in magnitude of lateral displacements of all light from a set of a galaxy’s stellar sources with a relative transverse motions of 200-250 km/s relative to an earth observer will always be less than the total difference in magnitude of lateral displacements of all light from a set of a galaxy’s stellar sources with relative transverse motions of only +-25km/s relative to the earth observer (Fig1). In other words, this paper proposes here that light incident on the earth observers image plane from a galaxy that rotates with our Milky Way should always be more distorted and blurred due to a greater magnitude of lateral displacements at the image plane due to stellar aberration. Than light incident on the image plane from any spiral galaxy that rotates oppositely to our Milky Way at any similar redshift distance.
Fig 1) A is earth observer and V is relative transverse velocity axis between stellar source and earth observer. Angle x is larger than angle y. Angle x represents range of incident angles of light from galaxies that rotate with the Milky Way and angle y represents range of incident angles of light from galaxies that rotate in opposite directions to the Milky Way. Due to the effects of stellar aberration, light from a galaxy rotating with the Milky Way will arrive with a greater range of incident angles x than the range of incident angles y of light arriving from a galaxy that rotates in the opposite direction to the Milky Way (1). This difference in the range of incident angles between x and y will result in smaller lateral displacements of the galaxy light incident for y at the image plane than the greater range of lateral displacements of light for x at the image plane. And result in this papers’ predicted increased blurring for light arriving at x, than for light arriving at y. The size in arc seconds of any galaxy at the earth observer’s camera image plane becomes proportionately smaller for progressively higher redshifts (taking up less pixels at image plane for higher redshift galaxies). But the 2 relative transverse velocity ranges between any spiral galaxy and the earth observer will always be the same between any redshift galaxy and the earth observer (-+25km/s for co rotating, 200-250km/s for counter rotating*). It follows then that these 2 ratios of image size decreasing with increased redshift vs constant relative transverse velocity between earth and any spiral galaxy at any redshift; will result in a progressively apparent (but not real) increase of blurring of galaxy images at higher redshifts due to stellar aberration. And additionally, should effect a greater amount of blurring of co rotating galaxies than counter rotating galaxies at higher redshifts due to the relative velocity differences between the 2 ratios*. This increased blurring effect for higher redshifts will therefore make it harder to identify co rotating galaxy rotation directions than counter rotating galaxies at progressively higher redshifts.
Fig 2) Three illustrations showing how stellar aberration can displace light from individual stars in a spiral galaxy’s arm to effectively “blur” the galaxies image. Showing different amounts of blurring for different directions of relative galactic rotation between a galaxy and the earth observer. Left is a starfield with no aberration from no relative transverse velocities between all the stars in the galaxy and earth observer. Centre is with a small range of Stellar Aberration from a galaxy that rotates oppositely to the earth observer. Right is with the larger range of Stellar aberration from a galaxy that rotates with the Milky Way. Notice how the co rotating galaxy’s starfield illustrated on the right is more spread out and diffuse due to a larger range of displacements of each stars position within the galaxy due to stellar aberration.
Conclusion
Classical non-relativistic Stellar aberration theory (1), when applied to light from external galaxies, should effect different ranges of displacement of stellar light coming from spiral galaxies as it arrives at the earth observers image plane due to the observed range of different rotational velocities of stars around galaxy cores (1,2,3,4). As a consequence, it is proposed here in this paper that the predicted range of displacements at the earth observers image plane should be greater for all stellar light coming from galaxies that rotate with our Milky Way than for all stellar light coming from spiral galaxies that rotate in an opposite direction to our Milky Way. And further to this it is proposed here that this stellar aberration effect should manifest itself as different amounts of blurring of images of spiral galaxies. And that this blurring effect should be greater for galaxies that have relatively lower transverse rotational velocities relative to an earth observer. And therefore, light arriving at the earth observers image plane from a galaxy that rotates in the same direction as our own Milky Way should appear to be more blurred than a galaxy that rotates in an opposite direction to our Milky Way for spiral galaxies at similar redshifts. And as a conclusion it is proposed here that this purely classical effect of stellar aberration is predicted to make the rotation direction of a galaxy that rotates in the same direction as the milky way harder to identify than any galaxy that rotates oppositely to our own Milky Way at any similar redshift.
Reference
1)Aberration (astronomy) page at Wikipedia.org/wiki/Aberration_Astronomy
2) https://commons.wikimedia.org/wiki/File:Rotation_curve_(Milky_Way).svg
3) Median Statistics Estimate of the Galactic Rotational Velocity.Tia Camarillo et al
4)Comparison of Rotation Curves of different Galaxy Types. Roberts & Rots, 1973
