Starship Asterisk*

MarkBour wrote:

Ann wrote:... Finally, note the one blue object in the picture, a star near small-looking galaxy NGC 4217 at 5 o'clock. The blue star is HD 106420, a B8V star with a color index as blue as -0.125 ± 0.013. The absence of any other strikingly blue objects in the field is a reminder how rare these blue stars really are ... Ann

Thanks for pointing that out. I really like the contrast there among the three stars that are visually near each other. They appear white(ish), red, and blue to my eye.

But it appears to me that there are also some serious blue patches in M106 in the image as well (?)

The link in the "Image Credit" goes to a blog of Mr. Feltoti's, which is very nice (and has some of the data).

Ann wrote:... Finally, note the one blue object in the picture, a star near small-looking galaxy NGC 4217 at 5 o'clock. The blue star is HD 106420, a B8V star with a color index as blue as -0.125 ± 0.013. The absence of any other strikingly blue objects in the field is a reminder how rare these blue stars really are ... Ann

https://en.wikipedia.org/wiki/Messier_106 wrote:

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[b][color=#0000FF]In this composite image of spiral galaxy M106 (NGC 4258), optical data from the Digitized Sky Survey is shown as yellow, radio data from the Very Large Array appears as purple, X-ray data from Chandra is coded blue, and infrared data from the Spitzer Space Telescope appears red. Two anomalous arms, which aren't visible at optical wavelengths, appear as purple and blue emission.[/color][/b]

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Amateur astronomer Robert Gendler retrieved archival Hubble images of M 106 to assemble a mosaic of the centre of the galaxy. He then used his own and fellow astrophotographer Jay GaBany’s observations of M 106 to combine with the Hubble data in areas where there was less coverage, and finally, to fill in the holes and gaps where no Hubble data existed. The centre of the galaxy is composed almost entirely of Hubble data taken by the Advanced Camera for Surveys, Wide Field Camera 3, and Wide Field and Planetary Camera 2 detectors. The outer spiral arms are predominantly HST data colourised with ground-based data taken by Gendler’s and GaBany’s 12.5-inch and 20-inch telescopes, located in New Mexico.

<<Messier 106 is one of the brightest and nearest spiral galaxies to our own. Despite its appearance, which looks much like countless other galaxies, Messier 106 hides a number of secrets. At its heart, as in most spiral galaxies, is a supermassive black hole, but this one is particularly active. Unlike the black hole at the centre of the Milky Way, which pulls in wisps of gas only occasionally, Messier 106’s black hole is actively gobbling up material. As the gas spirals towards the [1.6 AU wide] black hole, it heats up and emits powerful radiation. Part of the emission [within one light year of the black hole] is produced by a process that is somewhat similar to that in a laser - although here the process produces bright microwave radiation. As well as this microwave emission from Messier 106’s heart, the galaxy has another startling feature - instead of two spiral arms, it appears to have four. Although the second pair of arms can be seen in visible light images as ghostly wisps of gas they are even more prominent in observations made outside of the visible spectrum, such as those using X-ray or radio waves. Unlike the normal arms, these two extra arms are made up of hot gas rather than stars, and their origin remained unexplained until recently. Astronomers think that these, like the microwave emission from the galactic centre, are caused by the black hole at Messier 106’s heart, and so are a totally different phenomenon from the galaxy’s normal, star-filled arms. The extra arms appear to be an indirect result of jets of material produced by the violent churning of matter around the black hole. As these jets travel through the galactic matter they disrupt and heat up the surrounding gas, which in turn excites the denser gas in the galactic plane and causes it to glow brightly. This denser gas closer to the centre of the galaxy is tightly-bound, and so the arms appear to be straight. However, the looser disc gas further out is blown above or below the disc in the opposite direction from the jet, so that the gas curves out of the disc — producing the arching red arms seen here. Despite carrying his name, Messier 106 was neither discovered nor catalogued by the renowned 18th century astronomer Charles Messier. Discovered by his assistant, Pierre Méchain, the galaxy was never added to the catalogue in his lifetime. Along with six other objects discovered but not logged by the pair, Messier 106 was posthumously added to the Messier catalogue in the 20th century.

Lasers work when light stimulates emission of more light from a cloud of excited gas, with the original light in effect being amplified (the word laser is an acronym for light amplification by the stimulated emission of radiation). The centre of M106 harbours a similar phenomenon called a maser (short for microwave amplification by the stimulated emission of radiation), in which microwave radiation, which is at longer wavelengths than visible light, is emitted. Note that unlike man-made lasers, which are designed to produce a narrow beam, astronomical masers shine in all directions.>>

Ann wrote:Today's APOD is a reminder of the fact that a lot of modern astrophotography shows us details that our eyes could never see. It is in fact humanly impossible to see the pink color of emission nebulas with our eyes, because our eyes are too insensitive to their deep red light.