The Main Observation Problem, Challenging Astronomy, Solved Today
Vanishing Stars and “Triple Transient” 80-Year-Long Mystery
In July 1952, a curious incident happened at California’s Palomar Observatory, as astronomers photographed the night sky. At 8:52PM, one of their images shows three stars clustered together. Less than an hour later, at 9:45PM, the same astronomers photographed the same part of sky, and the stars had vanished:
Since then, stars vanishing (single or multiple in an area) have been observed hundreds of times. And there is still uncertainty on why and how that happens. Here is a typical recent article on this subject:
In simple terms, the justification is the following:
Time in the Universe is not homogenous: in some areas it runs faster or slower than in other areas. Amazingly, light takes not the shortest path, but the fastest path(s). If somewhere on the line of sight from a star to us, there is a spot/area of slow time, then, for that light, it might be faster to bend around such slower area than go straight through. (Besides that, there is a simple Snell’s law that explains light diffraction in star observations.) Why are scientists still not sure? Because usually star images after lensing / refraction become irregularly shaped and fuzzy like in the image of Einstein’s Cross below:
But the images of stars before they have disappeared were of regular shape, even in this “Triple Transient” image from 1952:
There was no progress in solving this problem until now, when in “Science of Visibility and Invisibility” we explained that an object / atom / particle moving at velocity V and wobbling at speed Δv is visible from certain positions only:
Line of sight should be inside a certain visibility cone but outside a certain invisibility cone. It is only the case when Δv<V — when vibrations are slower than the velocity of the object.
Let’s estimate velocities V and vibrations Δv for stars. What are the top velocities of the stars ever measured? 2,285 km/sec for a “free/linear” star, and 24,000 km/sec for a “rotating/confined” star (orbiting “supermassive Black Hole” at our Milky Way galactic center).
What does wobble in a star that we see? — Atoms (Hydrogen mostly) and plasma (protons and electrons mostly) on the star surface. (Check recent The Sun is NOT a Plasma — Don’t Parrot! - author shows that temperature not enough for plasma formation, but he forgets the major photoelectric effect ionizing star surface). Speed of such wobbling is determined by the temperature on a visible star surface (photosphere), and such speed is called “thermal velocity”. Surface temperature depends on a star, some have 2,000 Kelvin, others 50,000 Kelvin; for our Sun it is about 6,000 K (Kelvin). Now, for room temperature at about 300 K, thermal velocity of Hydrogen atoms was measured as 1.8 km/sec. From that, we can estimate Hydrogen thermal velocity at 2,000 K (and 50,000 K), because thermal velocity is proportional to the square root of temperature:
1.8 km/sec × sqrt (2,000 K / 300 K) ≈ 4.7 km/sec for 2,000 K
1.8 km/sec × sqrt (50,000 K / 300 K) ≈ 23.3 km/sec for 50,000 K
Besides that, thermal velocity of a particle is inversely related to the square root of the particle mass. Thus, because Hydrogen and a proton have the same mass, the thermal velocity of protons is the same as of Hydrogen. Electrons are 2,000 times lighter than protons, thus, thermal velocity of electron is larger than proton’s thermal velocity by a factor of sqrt(2000):
4.7 km/sec × sqrt (2,000) ≈ 210 km/sec at 2,000 K
23.3 km/sec × sqrt (2,000) ≈ 1,000 km/sec at 50,000 K
Thermal velocity / wobbling of electrons at 50,000 K is Δv ≈ 1,000 km/sec, which is still less than some stars’ velocity, for example V=2,285 km/sec for the “free/linear” star that we mentioned. There are various combinations between star surface temperatures and star velocities, when Δv<V. And such stars are visible only inside a certain cone, but outside some inner cone, with both cones centered along the star velocity. Here is a flat drawing (depicting just angles instead of 3D cones) explaining stars’ observation:
On this picture, outer (visibility) cone has angle β with V (and angle β can be greater than 90°, as it is drawn in this case). Inner (invisibility) cone has angle α with V; line of sight, drawn between the star at S0 and observer O2, has angle θ with V. For α ≤ θ ≤ β the star is visible.
Within one hour, the star moved from position S0 to position S1.
- Observer O1 did not see the star during that hour, and he won’t see it in future.
- For the observer O2 star vanished: he saw it (as S0) at the beginning of the hour, but not at the end (as S1).
- Observer O3 saw the star during the whole hour.
- For the observer O4 the star appeared: he did not see it at the beginning of the hour (at S0), but saw it at the end (at S1).
- Observer O5 did not see the star during that hour, but he will see it in future.
Problem solved.
P.S. In chapter 2 of Time Matters we discussed that stars change their velocity (both speed and direction) when entering or exiting arms in spiral galaxies, for example, in our Milky Way:
Change in a star velocity (along with change in location) can make visible star disappear for some observers, or vice versa — appear. We just have discussed a very similar incident in details. That is why some stars appear to us when entering arms and disappear from our perspective when exiting arms: star’s velocity vector changes dramatically on crossing an arm border, and so is the angle between the star’s velocity and the line of sight. Yet again, visibility depends on star temperature: hot stars tend to be visible everywhere. And slow stars, even if they are not very hot, will be visible anyway.
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