The Proceedings of the Eighth International Conference on Creationism (2018)

considerations this adiabatic expansion phase ought to end when the temperature in the outer portions of the SNR drops below 10 6 K. At this critical temperature, the ionized atoms begin to capture free electrons and lose energy by radiation. This radiative energy loss results in rapid cooling of the outer shell of the SNR and a transition to a third phase of its history. For ISM densities of 0.01-0.1 H atom/cm 3 , the Sedov phase is estimated last on the order of 100,000 years. The characteristics and behavior of the third phase, known as the ‘snowplow’ phase, has been obtained almost entirely from theoretical considerations and numerical modeling (see, for example, Blondin et al., 1998), as opposed to observation. It is known as the snowplow phase because the outer region of the SNR has become a slower moving, high-density cooler shell that expands like a snowplow into the surrounding ISM. It is also known as the radiative phase because the outer high-density shell is no longer ionized and radiates strongly in the visible part of the spectrum. The inner portion of the SNR, on the other hand, is still fully ionized, is expanding adiabatically, and pushes the cold outer shell outward, due to its pressure. Simple calculations on the time required for the inner SNR pressure to drop to that of the surrounding ISM suggest that the snowplow phase can potentially last for as long as a million years. However, several types of instabilities arise and tend to distort and disrupt the expanding SNR shell and reduce its lifetime (Blondin, 1998). Nevertheless, given that theory shows that SNRs in this phase radiate strongly and persist for hundreds of thousands of years, it is a profound puzzle why we do not observe many thousands of them in our galaxy, if the age of our galaxy truly exceeds a few hundred thousand years. Indeed, one is hard pressed to find even one good example of a radiative phase SNR reported in the astronomy literature. After almost additional 25 years of scientific study with much more powerful telescopes and techniques, how defensible today is Davies (1994) conclusion that, given the small number of observed Milky Way SNRs, our galaxy is at most only a few thousands of years old? The answer is that Davies primary findings still hold. First, the 2014 online catalog of SNRs maintained by Cambridge University (Green, 2014) reports a total of 294 observed Milky Way SNRs, while the count in the Davies paper was 205. This difference is obviously due to the improvement in sensitivity/resolution of radio telescopes over that interval. Davies also pointed out that there is a cutoff in SNR diameter at about 60 parsecs (about 200 light years) indicating that all the observed SNRs are at a relatively early stage in their histories. That is still valid. Davies emphasized that there are no observed SNRs in the third, or ‘snowplow’ stage in their histories. That also is still valid. However, the case is not as simple as Davies presented it. One reason, unfortunately, is an error in his analysis. Davies failed to include the observability factor of 47% in his estimate for the expected number of observable Sedov stage SNRs under his assumption that the galaxy is 7,000 years old. The figure that Davies used, 268, was obtained by dividing 7,000 years by the average time between SN events, which he took to be 25 years, to obtain 280, from which he subtracted 12, his estimate of the number of first-stage SNRs. Because our view from Earth of much of the rest of the galaxy is obstructed by the dust and stars in the galactic disk, it is essential to include this observability factor in any estimate of the number of observable galactic SNRs. For SNRs in the Sedov phase, that observability factor for the telescopes of 25 years ago was 47%. Davies did include that factor in his estimate of the expected number of observable SNRs were our galaxy much older than the SNR maximum lifetime, but he failed to include it for the case of a 7,000-year age. Including it in that case yields only 126 expected SNRs instead of 268. That number is notably fewer than the 200 actually observed as of 1994. On the face of things, that would suggest that either the galaxy is somewhat older than 7,000 years or else the estimated average time between SN explosions is too large. We suspect that the latter is the more likely explanation. Despite that oversight on Davies’ part, the 200 Sedov-stage SNRs actually observed compared with the 2256 SNRs expected if the age of the galaxy exceeds the Sedov-stage lifetime (Davies used an estimate of 120,000 years) is unaffected and striking. Sedov- stage SNRs are so bright that they remain detectable (apart from obstruction by dust and stars in the galactic disk) at galactic distances throughout their lifetimes. Even more striking is the fact that there are no observed third (snowplow) phase SNRs, given that they are expected to persist as readily detectible entities for hundreds of thousands of years. These conclusions still hold for the current catalog of observed SNRs in our galaxy. This is because the improvement in observability due to improvements in technology ought to scale the expected number of observed SNRs by the same factor as it has increased the actual number observed. That observability factor, instead of 0.47 in 1994, should now be on the order of (294/205) x 0.47 = 0.67. Davies (1994) also considered the neighboring galaxy known as the Large Magellanic Cloud (LMC) which lies about 160,000 light years from Earth and has a total stellar mass about a tenth that of the Milky Way. He points out that the number of SNRs actually observed in the LMC, a total of 29, is also smaller by large factor relative to the number expected (480) if the actual age of the LMC truly exceeded the Sedov-phase lifetime. With improved spatial resolution and sensitivity in the radio, infrared, optical, and X-ray surveys, the present SNR count in the LMC has increased to 47 (Seok et al., 2013; Badenes et al., 2010). But that number comes nowhere near to closing the gigantic gap between the number of SNRs observed and the number expected if the galaxy is old (Maoz and Badenes, 2010). The same is also the case for the nearby Small Magellanic Cloud, which has a total stellar mass about 7% that of our Milky Way and a total of 23 SNRs (Badenes et al., 2010). It is also the case for the galaxy known as M33 which is about 2.7 million light years away, has a mass about 10% that of the Milky Way, and contains about 100 SNRs (Long et al., 2010). In all three of these galaxies, there ought to be an abundance of observed radiative-phase SNRs if the galaxies were truly more than a few hundreds of thousands of years in age. But they are not observed. Therefore, the small number of SNRs in our own galaxy as well as in those close enough for radio, infrared, optical, and X-ray telescopes to image and count the individual SNRs is a significant indicator that the elapsed history of our own Milky Way galaxy and of those nearby is short, merely a few thousand years instead of the billions of years that the secularists assume. These SNR observations argue further that our CTC solution to the distant Tenev et al. ◀ Creation time coordinates solution to the starlight problem ▶ 2018 ICC 86