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View Full Version : Could Ghost-Like Object Found by Chandra Be Another ‘Voorwerp’?



Fraser
2009-May-29, 02:50 PM
The Chandra X-ray Observatory has found a cosmic “ghost” lurking around a distant supermassive black hole. Astronomers think this high-energy apparition is evidence of a huge eruption produced by the black hole. But this blue blob looks eerily similar to another cosmic blob of gas found by Galaxy Zoo member Hanny Van Arkel, [...]

More... (http://www.universetoday.com/2009/05/29/could-ghost-like-object-found-by-chandra-be-another-voorwerp/)

01101001
2009-May-29, 03:46 PM
Galaxy Zoo member Hanny Van Arkel, [...]

And BAUT Forum member! Hanny (http://www.bautforum.com/members/hanny.html)

slang
2009-May-29, 11:03 PM
And Happy Birthday, Hanny! Having Hubble back up and running must be a great advance birthday gift.

Middenrat
2009-May-30, 03:46 AM
In the UT article it states Hanny's Voorwerp was originally imaged blue, before spectral analysis bumped it to green. Was that a Doppler effect adjustment?
Supplemental on that answer: is there a perceived difference in colour due to cosmic expansion?

ngc3314
2009-May-30, 04:22 AM
In the UT article it states Hanny's Voorwerp was originally imaged blue, before spectral analysis bumped it to green. Was that a Doppler effect adjustment?
Supplemental on that answer: is there a perceived difference in colour due to cosmic expansion?

The original discovery was from a color rendition of the Sloan Digital Sky Survey image, which maps the gri filters to visual BGR. This gets natural colors just about right for most galaxies, but misses badly for objects with very strong emission lines (like Hanny's Voorwerp). Using, say, BVR filters shows the dominant color as green from the strong emission lines much like those in planetary nebulae. (Some sample images may be seen here (http://www.astr.ua.edu/keel/research/voorwerp.html)). There might just barely be a perceptible color difference from its redshift (the strong oxygen emission line is shifted from 500.7 to 525.2 nm) if it were bright enough for good color vision, but visually it's so dim that I know of only two people (with quite large telescopes in west Texas) who have seen it directly at all (way below the color-vision threshold).

Middenrat
2009-May-30, 04:43 AM
Thankyou ngc3314, that was illuminating.
In the article a much further distant object was discussed, a remnant of a black hole emission event occurring BB+3bn years ago. What would the nm shift be at that range?
Thanking you in advance.

ngc3314
2009-May-30, 02:15 PM
Thankyou ngc3314, that was illuminating.
In the article a much further distant object was discussed, a remnant of a black hole emission event occurring BB+3bn years ago. What would the nm shift be at that range?
Thanking you in advance.

The manuscript by Fabian et al. (on arxiv.org) lists the redshift of HDF 130 as z=1.99. In general, the wavelengths we see from an object at redshift z are stretched so we observe them at a factor (1+z) times the emitted value. So in that case, the [O III] emission line at 500.7 nm will be observed in the near-infrared at 1502 nm, and what we see in the optical will have started out deep in the ultraviolet. By that redshift, for a spiky emission-line spectrum, there is no particular relationship between the colors we would have seen local to the object and those of the light we actually observe.

Middenrat
2009-May-31, 02:51 AM
That answer makes me glad my puny peepers can't see the whole universe, it would blow my mind. But I do feel a little closer to getting an intuitive grasp of the cosmos, thankyou for taking the trouble ngc3314.