Posts Tagged m31

Credit & Copyright: Martin Pugh, martinpughastrophotography.id.au

A beautiful APOD from the weekend.

The most distant object easily visible to the eye is M31, the great Andromeda Galaxy some two and a half million light-years away. But without a telescope, even this immense spiral galaxy – spanning over 200,000 light years – appears as a faint, nebulous cloud in the constellation Andromeda. In contrast, details of a bright yellow nucleus and dark winding dust lanes, are revealed in this digital telescopic image. Narrow band image data, recording emission from hydrogen atoms, shows off the reddish star-forming regions dotting gorgeous blue spiral arms and young star clusters While even casual skygazers are now inspired by the knowledge that there are many distant galaxies like M31, astronomers seriously debated this fundamental concept in the 20th century. Were these “spiral nebulae” simply outlying components of our own Milky Way Galaxy or were they instead “island universes” — distant systems of stars comparable to the Milky Way itself? This question was central to the famous Shapley-Curtis debate of 1920, which was later resolved by observations of M31 in favor of Andromeda, island universe.

Two views of the Andromeda Galaxy (M31), both by the formidable Robert Gendler.

Andromeda is the nearest major galaxy to our own Milky Way Galaxy. Our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies. The diffuse light from Andromeda is caused by the hundreds of billions of stars that compose it. The several distinct stars that surround Andromeda’s image are actually stars in our Galaxy that are well in front of the background object. Andromeda is frequently referred to as M31 since it is the 31st object on Messier’s list of diffuse sky objects. M31 is so distant it takes about two million years for light to reach us from there. Although visible without aid, the above image of M31 is a digital mosaic of 20 frames taken with a small telescope. Much about M31 remains unknown, including how it acquired its unusual double-peaked center.

The center of the Andromeda galaxy is beautiful but strange. Andromeda, indexed as M31, is so close to our own Milky Way Galaxy that it gives a unique perspective into galaxy composition by allowing us to see into its core. Billions of stars swarm around a center that has two nuclei and likely houses a supermassive black hole over 5 million times the mass of our Sun. M31 is about two million light years away and visible with the unaided eye towards the constellation of Andromeda, the princess. Pictured above, dark knots of dust are seen superposed on the inner 10,000 light years of M31′s core. The brighter stars are foreground stars located in our Milky Way Galaxy.