Spur of the Milky Way?
I may have discovered a new artifact of our Milky Way galaxy—a spur of young, hot, blue-white stars angling away from the galactic disk. Is it a real artifact of the galaxy, or is it a buggy artifact of the software used to model the stars in this region of the Milky Way? It could even be an artifact of imperfect data.
The Milky Way galaxy (our home city of stars) contains nearly a trillion (1,000,000,000,000) burning beacons of light like our sun. Some are old, some are young, some tiny and light-weight, and some are large and heavy. The small ones typically burn with a cooler flame more toward the red end of the spectrum. The large ones typically burn with a hotter flame far into the blue end. When stars reach old age, they start burning helium instead of hydrogen. This makes the star far larger and redder, like Antares (Alpha Scorpii)—a red giant star at the heart of the scorpion.
Antares and more than a dozen blue-white stars form an apparent spur sticking above the disk of the Milky Way. At least they do this in the 3D software, "Stars in the NeighborHood."
For the avid astronomer, the stars of this spur include, Antares, Chi Oph, Zeta Oph, Delta Sco, Sigma Sco, Beta 1 Sco, Omega 1 Sco, Sigma Lup, 22 Sco, Tau 1 Lup, Zeta Oph, Tau Sco and Rho Oph.
If it really is an artifact of the Milky Way, what could have caused it? Tidal wave of a nearby, dwarf galaxy? A massive black hole?
Stars in the NeighborHood Software
Have you ever wanted to know what the landscape of the galaxy looked like in our region of the Milky Way? That is why I created this software. Like pirates looking for the islands of the Caribbean, I wanted to know where the star clusters stood, and where the old, chemical-rich, garden spots of the galaxy were situated.
Also called "Stars in the Hood," this software, available at www.SpaceSoftware.Net, features two 3D views of our neck of the Milky Way on its main window. The view on the left shows a volume of space, variable in size, up to one "neighborhood" of stars (up to 32 parsecs or 104.4 light years on a side). This "cube" of space can be moved throughout our vicinity of the galaxy. The view on the right contains a much larger volume of space (192 parsecs or 626 light years across) for locating the smaller "Hood (or Viewing) Cube." This "Locator Cube" is also about the width of the galactic disk. The orientation of the cubes are based on the current Earth axis—North for up and South for down.
An additional 3D view comes on a different window called, "Zoom Out Universe." This view starts at Earth and zooms out by a factor of ten for each jump all the way to our Local Group of galaxies. Earth remains at the center of each of these views. At scale level "3," we see the galactic disk and the Solar region of the Milky Way. This is where the "spur" of bright stars can be seen.
Bug in the Software?
Every software developer hates bugs in their code. Hopefully, when a software program is shipped, all of the bugs have been found and eliminated. This rarely, if ever, happens. Still, a programmer can remain hopeful.
During the development of "Stars in the NeighborHood," one early bug involved a rounding off of values used to position the stars in the 3D cube "Viewing Cube" on the left. Many of the stars were found in evenly-spaced layers which proved to be immediately suspect. The source of the "round-off" error was quickly found and fixed.
Software developers frequently rely on the reports of software users for tracking down and eradicating bugs which happened to make it into the marketplace. The savvy user will report more than mere, "It doesn't work," or "The software is broken." The more specific the report, the easier it is for the software developer to duplicate the error condition in the laboratory, to track down the source of the error, and then to fix the problem.
Flaws in the Data
Sometimes, the software may be working properly, but the data creates unreal anomalies. One example of this occurred on the right-hand panel of the software—in the "Locator Cube." This panel displays major stars and nearby star clusters. The clusters include, the Hyades and Pleiades (both in Taurus), the Praesepe (Cancer), the Coma (Coma Berenices), and the Ursa Major.
When first displayed, each of these clusters exhibited an extreme elongation. Instead of roughly spherical, each cluster proved to be a long ellipsoid. The source of the flaw was immediately apparent. The long axis of each ellipsoid pointed directly at Sol (our sun) and Earth. This proved to be an artificial feature of the data. In other words, this Solar-centric artifact proved to be a flaw.
In astronomy, the two-dimensional positions of stars in the sky are known with a great deal of accuracy. The distances, however, are far less accurate. Each cluster seemed to radiate from Earth as if they were spokes on a wheel. This was because the distance to each star in the cluster is only a rough estimate. To remove this artificial feature required compressing each cluster so that they became more spherical.
How can scientists make such mistakes? It is not a mistake, really. It is only a limitation of the tools used to measure those distances. Try splitting a hair with a butcher knife or even a dull axe. Next to impossible.
Surveyors on Earth measure distances all of the time using simple, trigonometric math. To measure the distance across a canyon, for instance, can be accomplished by taking two accurate readings from two widely separated points. All one needs from these measurements are the directions toward a distant point from two widely separated viewing locations; plus the accurate distance between those viewing locations. In our example of the canyon, it proves to be impossible to measure the distance by walking across the canyon with a tape measure. Walking on thin air is part of the problem. Finding a tape measure which is long enough is the other part.
The two widely-separated viewing locations, and the line connecting them, is called the "baseline." Say the first reading is perpendicular to the baseline. In other words, the line from the viewer to the distant object is at 90 degrees to the baseline. Say the second viewing location is ten meters from the first. If the view angle to the distant object is 89 degrees from the baseline at the second viewing location, then the distance to that distant object is,
tan (89°) = (distance / 10 meters)
57.29 x 10 meters = distance
distance = 572.9 meters.
More accurate distances can be gained from wider baselines. How wide is the baseline astronomers use? The diameter of the Earth's orbit around the sun gives us a baseline of 186 million miles (about 300 million kilometers = 3.0 x 108 km).
How can we increase our baseline? The next time NASA, or some other space agency, sends a spacecraft outside of the Solar system, if it includes a camera and a telescope, the baseline could be several billion miles long. Of course, this only works for stars at near right angles to the path of the spacecraft.
The farther a star is away from the measuring baseline, the smaller the angle measured from the two locations on the baseline. The closer stars are fractions of a second of arc in angle from the two measuring points. Angles are measured in degrees, with sixty minutes to a degree, and sixty seconds to a minute.
At about thirty parsecs (100 light years), the angle measured is roughly equivalent to the possible error in measurement. This is where scientists are "splitting hairs." The word "parsec," by the way, comes from "PARallax SECond of arc," and refers to the apparent angle created by the parallax of view when seen from two viewpoints. You get parallax all the time, if you have two eyes with which to see. This is how we judge 3D depth in our field of view.
There are other methods of measuring distance. One is by star type. This contains more variables and is thus less accurate in some respects, but for the very distant stars, it is far better than nothing. Such variables include age of the star, chemical composition, mass of the star, and the amount of dust and gas between the star and Earth. All a scientist can hope for here is an educated guess.
The dead giveaway for this spurious spur is that it seems to be sticking out of the galaxy at Earth's location. In other words, it is a radial distortion centered on Sol and Earth. And this means that it is likely a problem with the published distances to those stars.
Oh, well! And I thought I had made the next great discovery in astronomy.
At least, when we see figures for star distances, we know that they are only approximations. And in this case, the distances to many of those bright, remote stars are too large. Those stars are a little closer than we thought.
This Hub was nominated in the Top of the Class contest held in early 2011. Though it did not win, I am grateful that it received mention by its nomination.
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