Ring around a gravitational lens.Ring around a gravitational lens gravitational lens
A massive celestial object, such as a galaxy, whose gravity bends and focuses the light of a more distant object, resulting in a magnified, distorted, or multiple image of the original light source for a distant observer.
Early this year, two astronomers announced the discovery of what appeared to be huge arcs of luminous matter associated with two small clusters of distant galaxies (SN: 1/17/87, p.36). If real, these sausage-shaped arcs, which are hundreds of thousands of light-years long, might have been an entirely new kind of astronomical object Astronomical objects are significant physical entities, associations or structures which current science has confirmed to exist in space. This does not necessarily mean that more current science will not disprove their existence. or evidence of fantastically energetic processes going on at the cluster.
Now, however, the two astronomers announce that spectroscopic spec·tro·scope
An instrument for producing and observing spectra.
spectro·scop study of one of the arcs convinces them that it is a kind of optical illusion, an image formed by a gravitational lens.
A strong gravitational field Noun 1. gravitational field - a field of force surrounding a body of finite mass
field of force, force field, field - the space around a radiating body within which its electromagnetic oscillations can exert force on another similar body not in contact with it , like that of this galaxy cluster called Abell 370, will bend rays of light coming from a more distant object. It can act like a lens distorting the image of the more distant object.
The spectrum of an object like the arc characteristically shows a continuous rainbow background with bright or dark lines representing resonant emissions or absorptions by different chemical substances superimposed su·per·im·pose
tr.v. su·per·im·posed, su·per·im·pos·ing, su·per·im·pos·es
1. To lay or place (something) on or over something else.
2. . As the expansion of the universe is carrying distant galaxies away from us, these resonance lines will appear shifted to the red by some amount from the wavelengths at which they appear at rest in the laboratory. The trick is to identify the lines properly and determine the amount of redshift redshift
Displacement of the spectrum of an astronomical object toward longer wavelengths (visible light shifts toward the red end of the spectrum). In 1929 Edwin Hubble reported that distant galaxies had redshifts proportionate to their distances (see .
In the spectrum of this arc is one prominent emission line, note Vahe Petrosian of Stanford University and C. Roger Lynds of Kitt Peak National Observatory Kitt Peak National Observatory, astronomical observatory located southwest of Tucson, Ariz.; it was founded in 1958 under contract with the National Science Foundation and is administered by the Association of Universities for Research in Astronomy. in Tucson, Ariz. If the arc is real matter and associated with the cluster, that line can be identified as an emission of ionized i·on·ize
tr. & intr.v. i·on·ized, i·on·iz·ing, i·on·iz·es
To convert or be converted totally or partially into ions.
i helium. However, as Lynds puts it, "Since September we've been processing the data with greater and greater care to try to reveal and confirm any spectroscopic features other than the one strong emission line.' This study showed that the spectrum lacks the pattern of fainter lines usually associated with the helium line.
The alternative is to identify the bright line as an emission of oxygen, for which an accompanying pattern of faint lines does appear in the arc's spectrum. That means, however, that the light in the arc is actually coming from something twice as far away as the cluster Abell 370.
The theory of gravitational lenses says that if the lensed object, the lens and the observer are perfectly in line, the lens should make an image in the form of a circular ring. This appears to be almost such a case, with part of the ring present. The rest may be suppressed by the presence of a second lens, Petrosian suggests. Abell 370 actually has two closely spaced concentrations of mass, he points out.