Distance
Until recently the distance to the supernova remnant was estimated at about 2500 light-years. Recent studies, however, have shown that it must be closer. In 1999, William Blair, assuming that the shock wave should be expanding at the same rate in all directions, compared the angular expansion along the sides of the bubble (visible in Hubble Space Telescope images) with direct line-of-sight measurements of the radial expansion towards the Earth. He concluded that the actual size of the bubble was about 40% smaller than the conventional value, leading to a distance of about 1470 ly.
This revised calculation, though it involved some uncertainty and was met with some resistance, has been substantially corroborated by the discovery via the Far Ultraviolet Spectroscopic Explorer (FUSE) of a star behind the Veil. The star, KPD2055+3111, of spectral type sdOBwas, was identified as UV-bright in an image from the Ultraviolet Imaging Telescope, and absorption lines in its spectrum indicate that its light is partially intercepted by the supernova remnant. The emission properties of the star indicate that it lies about 1860 ly away, giving an upper bound for the distance of the loop and supporting the previous estimate of 1470 ly.
The revised distance in turn yields revised estimates of the size of the remnant (to 90 ly, down from 150 ly previously) and for its age (now thought to be between 5000 to 8000 years).
Read more about this topic: Cygnus Loop
Famous quotes containing the word distance:
“It is the simplest relation of phenomena, and describes the commonest sensations with more truth than science does, and the latter at a distance slowly mimics its style and methods.”
—Henry David Thoreau (1817–1862)
“The mystery of the evening-star brilliant in silence and distance between the downward-surging plunge of the sun and the vast, hollow seething of inpouring night. The magnificence of the watchful morning-star, that watches between the night and the day, the gleaming clue to the two opposites.”
—D.H. (David Herbert)
“Let me approach at least, and touch thy hand.
[Samson:] Not for thy life, lest fierce remembrance wake
My sudden rage to tear thee joint by joint.
At distance I forgive thee, go with that;
Bewail thy falsehood, and the pious works
It hath brought forth to make thee memorable
Among illustrious women, faithful wives:
Cherish thy hast’n’d widowhood with the gold
Of Matrimonial treason: so farewel.”
—John Milton (1608–1674)