Universe Today
Description:
"The distance to the Whirlpool galaxy (M51, NGC 5194) is estimated using published photometry and spectroscopy of the Type II-P supernova SN 2005cs. Both the expanding photosphere method (EPM) and the standard candle method (SCM), suitable for SNe II-P, were applied. The average distance (7.1 +/- 1.2 Mpc) is in good agreement with earlier surface brightness fluctuation and planetary nebulae luminosity function based distances, but slightly longer than the distance obtained by Baron et al. for SN 1994I via the spectral fitting expanding atmosphere method. Since SN 2005cs exhibited low expansion velocity during the plateau phase, similarly to SN 1999br, the constants of SCM were recalibrated including the data of SN 2005cs as well. The new relation is better constrained in the low-velocity regime, that may result in better distance estimates for such SNe."
"This sharpest-ever image of the Whirlpool Galaxy, taken in January 2005 with the Advanced Camera for Surveys aboard NASA's Hubble Space Telescope, illustrates a spiral galaxy's grand design, from its curving spiral arms, where young stars reside, to its yellowish central core, a home of older stars. At first glance, the compact galaxy appears to be tugging on the arm. Hubble's clear view, however, shows that NGC 5195 is passing behind the Whirlpool. The small galaxy has been gliding past the Whirlpool for hundreds of millions of years. As NGC 5195 drifts by, its gravitational muscle pumps up waves within the Whirlpool's pancake-shaped disk. The waves are like ripples in a pond generated when a rock is thrown in the water. When the waves pass through orbiting gas clouds within the disk, they squeeze the gaseous material along each arm's inner edge. The dark dusty material looks like gathering storm clouds. These dense clouds collapse, creating a wake of star birth, as seen in the bright pink star-forming regions. The largest stars eventually sweep away the dusty cocoons with a torrent of radiation, hurricane-like stellar winds, and shock waves from supernova blasts. Bright blue star clusters emerge from the mayhem, illuminating the Whirlpool's arms like city streetlights."
"This image of the core of the nearby spiral galaxy M51, taken with the Wide Field Planetary camera (in PC mode) on NASA's Hubble Space Telescope, shows a striking , dark "X" silhouetted across the galaxy's nucleus. The "X" is due to absorption by dust and marks the exact position of a black hole which may have a mass equivalent to one-million stars like the sun. The darkest bar may be an edge-on dust ring which is 100 light-years in diameter. The edge-on torus not only hides the black hole and accretion disk from being viewed directly from earth, but also determines the axis of a jet of high-speed plasma and confines radiation from the accretion disk to a pair of oppositely directed cones of light, which ionize gas caught in their beam. The second bar of the "X" could be a second disk seen edge on, or possibly rotating gas and dust in MS1 intersecting with the jets and ionization cones."
History of Observation:
"Very faint nebula, without stars, near the eye of the Northern Greyhound [hunting dog], below the star Eta of 2nd magnitude of the tail of Ursa Major: M. Messier discovered this nebula on October 13, 1773, while he was watching the comet visible at that time. One cannot see this nebula without difficulties with an ordinary telescope of 3.5 foot: Near it is a star of 8th magnitude. M. Messier reported its position on the Chart of the Comet observed in 1773 & 1774. It is double, each has a bright center, which are separated 4'35". The two "atmospheres" touch each other, the one is even fainter than the other."
"This very singular object is thus described by Messier: - "Nebuleuse sans etoiles." "On ne peut la voir que difficilement avec une lunette ordinaire de 3 1/2 pieds." "Elle est double, ayant chacune un centre brillant eloigne l'un de l'autre de 4' 35". Les deux atmospheres se touchent." By this description it is evident that the peculiar phenomena of the nebulous ring which encircles the central nucleus had escaped his observation, as might have been expected from the inferior light of his telescopes. My Father describes it in his observations of Messier's nebulae as a bright round nebula, surrounded by a halo or glory at a distance from it, and accompanied by a companion; but I do not find that the partial subdivision of the ring into two branches throughout its south following limb was noticed by him. This is, however, one of its most remarkable and interesting features. Supposing it to consist of stars, the appearance it would present to a spectator placed on a planet attendant on one of them eccentrically situated towards the north preceding quarter of the central mass, would be exactly similar to that of our Milky Way, traversing in a manner precisely analogous the firmament of large stars, into which the central cluster would be seen projected, and (owing to its distance) appearing, like it, to consist of stars much smaller than those in other parts of the heavens. Can it, then, be that we have here a brother-system bearing a real physical resemblance and strong analogy of structure to our own? Were it not for the subdivision of the ring, the most obvious analogy would be that of the system of Saturn, and the idea of Laplace respecting the formation of that system would be powerfully recalled by this object. But it is evident that all idea of symmetry caused by rotation on an axis must be relinquished, when we consider that the elliptic form of the inner subdivided portion indicates with extreme probability an elevation of that portion above the plane of the rest, so that the real form must be that of a ring split through half its circumference, and having the split portions set asunder at an angle of about 45 deg each to the plane of the other."
"The greater part of the observations were made when the eye was affected by lamp-light, which made it difficult to estimate correctly the centre of the nucleus; it was of importance that no time should be unnecessarily spent, and after the lamp had been used a new measure was taken, as it was judged that the object was sufficiently seen. With the brighter stars this would frequently happen before the nucleus was well defined, as all impediments to vision seem to affect nebulae much more than stars the light of which would be estimated as of the same intensity. In the foregoing list the greatest discrepancies are in the measures of bright objects, and this is probably the proper account of it. No stars have been inserted in the sketch which are not in the table of the measurements. The general appearance of the object would have been better given if the minute stars had been put in from the eye-sketch, but it would have created confusion."