Gravity lens: definition, types, modeling

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Gravity lens: definition, types, modeling
Gravity lens: definition, types, modeling

A gravitational lens is a distribution of matter (for example, a cluster of galaxies) between a distant light source, which is capable of bending the radiance from the satellite, passing towards the viewer, and the observer. This effect is known as gravitational lensing, and the amount of bending is one of Albert Einstein's predictions in general relativity. Classical physics also talks about the bending of light, but that's only half of what general relativity talks about.


Gravitational lens, types and definition

Although Einstein made unpublished calculations on this subject in 1912, Orest Chwolson (1924) and František Link (1936) are generally considered to be the first to articulate the effect of the gravitational lens. However, he is still more commonly associated with Einstein, who published a paper in 1936.

Confirmation of the theory

Gravitational Lens, Modeling and Views

Fritz Zwicky suggested in 1937 that this effect could allow galaxy clusters to act as a gravitational lens. Only in 1979, this phenomenon was confirmed by the observation of the quasar Twin QSO SBS 0957 + 561.


Gravity lens

Unlike an optical lens, a gravitational lens produces the maximum deflection of light that passes closest to its center. And the minimum of the one that extends further. Therefore, a gravitational lens does not have a single focal point, but does have a line. This term in the context of light deflection was first used by O.J. Lodge. He noted that "it is unacceptable to say that the sun's gravitational lens acts in this way, since the star does not have a focal length."

If the source, the massive object, and the observer lie in a straight line, the source light will appear as a ring around matter. If there is any offset, only the segment can be seen instead. This gravitational lens was first mentioned in 1924 in St. Petersburg by the physicist Orest Khvolson and quantitatively worked out by Albert Einstein in 1936. Generally referred to in the literature as Albert rings, as the former was not concerned with flow or image radius.

Most often, when the lensing mass is complex (such as a group of galaxies or a cluster) and does not cause a spherical distortion of space-time, the source will resemblepartial arcs scattered around the lens. The observer can then see multiple resized images of the same object. Their number and shape depend on the relative position, as well as on the simulation of gravitational lenses.

Three classes

Gravitational lens, types

1. Strong lensing.

Where there are easily visible distortions, such as the formation of Einstein rings, arcs and multiple images.

2. Weak lensing.

Where the change in background sources is much smaller and can only be detected by statistical analysis of a large number of objects to find only a few percent coherent data. The lens shows statistically how the preferred stretching of the background materials is perpendicular to the direction towards the center. By measuring the shape and orientation of a large number of distant galaxies, their locations can be averaged to measure lensing field shift in any region. This, in turn, can be used to reconstruct the mass distribution: in particular, the background separation of dark matter can be reconstructed. Because galaxies are inherently elliptical and the weak gravitational lens signal is small, very large numbers of galaxies must be used in these studies. Weak lens data must carefully avoid a number of important sources of bias: internal shape, the tendency of the camera's point spread function to distort, and the ability of atmospheric vision to change images.

The results of thesestudies are important for evaluating gravitational lenses in space to better understand and improve the Lambda-CDM model and to provide a consistency check on other observations. They may also provide an important future constraint on dark energy.

3. Microlensing.

Where no distortion is visible in the shape, but the amount of light received from the background object changes over time. The object of lensing can be stars in the Milky Way, and the source of the background is balls in a distant galaxy or, in another case, an even more distant quasar. The effect is small, so that even a galaxy with a mass greater than 100 billion times that of the Sun would produce multiple images separated by only a couple of arcseconds. Galactic clusters can produce separations of minutes. In both cases, the sources are quite far away, many hundreds of megaparsecs from our universe.

Time delays

Gravitational lens, definition

Gravity lenses act equally on all types of electromagnetic radiation, not just visible light. Weak effects are studied both for the cosmic microwave background and for galactic studies. Strong lenses were also observed in radio and X-ray modes. If such an object produces multiple images, there will be a relative time delay between the two paths. That is, on one lens, the description will be observed earlier than on the other.

Three types of objects

Gravitational lens, modeling

1. Stars, remnants, brown dwarfs andplanets.

When an object in the Milky Way passes between Earth and a distant star, it will focus and intensify the background light. Several events of this type have been observed in the Large Magellanic Cloud, a small universe near the Milky Way.

2. Galaxies.

Massive planets can also act as gravitational lenses. Light from a source behind the universe is bent and focused to create images.

3. Galaxy clusters.

A massive object can create images of a distant object lying behind it, usually in the form of stretched arcs - a sector of the Einstein ring. Cluster gravitational lenses make it possible to observe luminaries that are too far away or too faint to be seen. And since looking at great distances means looking into the past, humanity gains access to information about the early Universe.

Solar gravity lens

Albert Einstein predicted in 1936 that rays of light in the same direction as the edges of the main star would converge to a focus at about 542 AU. So a probe that far (or more) from the Sun can use it as a gravitational lens to magnify distant objects on the opposite side. The location of the probe can be moved as needed to select different targets.

Drake Probe

This distance is far beyond the advancement and capability of space probe equipment such as Voyager 1, and beyond known planets, although for millenniaSedna will move further in its highly elliptical orbit. The high gain for potentially detecting signals through this lens, such as microwaves on a 21 cm hydrogen line, led Frank Drake to speculate in the early days of SETI that a probe could be sent that far. The multipurpose SETISAIL and later FOCAL were proposed by ESA in 1993.

But as expected, this is a difficult task. If the probe passes 542 AU, the objective's magnification capabilities will continue to operate at longer distances, as rays that come into focus at larger distances travel farther away from the solar corona distortion. A critique of this concept was given by Landis, who discussed issues such as interference, high target magnification that would make it difficult to design the mission's focal plane, and analysis of the lens's own spherical aberration.

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