![]() ![]() While most yellow supergiants aren't expected to go supernova when they finish out their lives, the team said it's possible that the star was actually a binary star. They narrowed their search to a yellow supergiant star (visible in Hubble Space Telescope pictures) that was there before the explosion, and appears to be missing afterwards. After the event, astronomers scoured older pictures to see if they could find the source of the explosion. The latest supernova, called SN 2011dh, was at its brightest in June 2011 before slipping back into obscurity. "Three supernovas in 17 years is a lot for single galaxy, and reasons for the supernova surge in M51 are being debated," noted the NASA website Astronomy Picture of the Day in 2011, without elaborating on the possible explanations. Skywatchers recorded supernovas in 1994, 20. There's been a veritable cornucopia of supernovas in the Whirlpool in recent years. (Image credit: Conrad Jung) Supernova bonanza The image on the left was taken in 2009, and on the right July 8th, 2011. I propose three regions of spiral structure in M51: (1) the extended tidal arm created by the previous passage of NGC 5195 (2) the strong tidal arms seen in the optical and created by the most recent passage 70 to 84 million years ago and (3) the inner density wave excited by these tidal arms.The Whirlpool galaxy (M51) before (left) and after (right) the eruption of supernova SN 2011dh in May 2011. ![]() The inner structure is consistent with resonantly excited m = 2 Lindblad dispersion orbits. The transition between the directly excited outer tidal arms and the indirectly excited inner arms explains the symmetrically placed bends in the outer arms of M51. The outer arms of M51 behave like material arms inward to ~140^. I interpret the extended HI tail as a remnant of an earlier passage of the companion. The orbit and decay time estimates imply that the companion is in a shrinking orbit and will eventually merge with M51. This indicates that the highly disturbed companion's mass/luminosity is somewhat abnormal. The mass of NGC 5195 must be roughly 1/10 the mass of M51 to produce a good match. The simulation also refines the limits for the ratio of halo mass to disk mass for M51 to be between 1.0 and 3.0. The simulation reproduces the radii and azimuths of points along the sharp dust lane spiral arms, the general shape of the disk seen in the IR, and the clumps seen in HI north of the companion. The position angle of maximum tidal action is ~300^ circ. I find that the entire grand design structure in M51 is consistent with a tidal passage of its companion, NGC 5195, in an osculating orbit (i = 50^circ, e = 0.1, a = 16.6 kpc) roughly 70 million years ago (H = 50 (km/sec)/Mpc). This method is suitable for nearly face-on grand design galaxies with companions. I develop an analytic method to set limits to some of the orbit parameters. I also include a simple gas cloud collision algorithm that permits features in the gas particles to strengthen. The problem reduces to choosing a finite set of orbits (for NGC 5195) that can model the observed features of M51. I model the grand design spiral galaxy M51 (NGC 5194) as an interacting system and use a three component self-gravitating N-body code to simulate the gravitational interaction. ![]()
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