According to Einstein’s theory of general relativity, gravity can change the curve of space-time; As a result, the path of light changes due to collisions with a gravitational field. For decades, astronomers used this theory to implement the Gravitational Lens (GL) project. According to the project, a remote source could be accessed through a massive mass.
Two theoretical physicists discuss the use of the sun to create a solar gravitational lens (SGL) in a new study. This powerful telescope can amplify light in such a way as to allow direct imaging of nearby extrasolar planets. In this way, astronomers can make sure that planets like Proxima b can be inhabited before sending a spacecraft.
The findings were recently published online and are set to be published in the journal Physical Review D. The researchers of this study Victor Toth, Theoretical physicist and Slavova Ji Torishev, NASA’s JPL physicist, is the lead researcher (PI) on the second phase of the NIAC, entitled “Direct Multi-Pixel Imaging and Extrasolar Spectroscopy with Solar Gravity Lens Mission.”
Gravitational lenses, in addition to being the basis for outstanding research in the field of astrophysics, can provide the ability to capture dramatic images of the universe. These images include phenomena such as “Einstein rings”. These rings are called light from distant objects, which are created by colliding with a gravitational field between a distant object and an observer.
Depending on the type of alignment between the observer and the remote source, and the lens, the source light may appear in the form of an arc, cross, or other shape. Any large object can be used as a gravitational lens; But the sun is in the best position for GL astronomy. To begin with, the largest mass in the solar system can be used as a powerful lens. Secondly, the focal area of the lens starts at an approximate distance of 550 astronomical units from the Sun, which is a realistic distance for the next mission. The focal area of the next large object (Jupiter) begins at a distance of more than 2,400 astronomical units.
In short, astronomers can adjust the alignment of the sun to create SGL and use it for astronomical observations such as observations of nearby extrasolar planets. Direct imaging is one of the most promising areas for identifying extrasolar planets and could revolutionize future studies of extrasolar planets. By examining light emitted directly from the planet’s atmosphere or surface, astronomers can gain access to a spectrum that reveals the building blocks of the planet’s atmosphere and even its vegetation.
This method is a bit difficult; However, because current telescopes do not have enough resolution to directly image smaller planets or rocky planets, most of the planets photographed are long-orbited gas giants. “Turishf says:
We need access to very large telescopes to directly observe and image the extrasolar planet; Therefore, if we want to see our Earth with a resolution of one pixel from a distance of one hundred light years, we will need a telescope with a diameter of approximately ninety kilometers. The diameter of future ground-based telescopes (Europe’s largest telescope) and space telescopes such as the James Webb Telescope are 39 meters and 5.6 meters, respectively. Also, the diameter of future concept designs such as LUVOIR and HabeX, which are supposed to be a replacement for these magnifying machines, will be 16 and 24 meters, respectively.
According to the current trend, the construction of huge node-kilometer telescopes may not be possible during the life of modern man or even his children and grandchildren; But with SGL, observations of orbiting extrasolar planets (such as Proxima b and c, or seven rocky planets in orbit around TRAPPIST-1) will be possible by the middle of the century. To investigate the feasibility of SGL, Toth and Toryshev referred to previous research that had developed a definition of wave theory for SGL. Finally, the Earth images were simulated at a resolution of 1024 by 1024 pixels, showing it in the added noise state (left) and after reconstruction (right).
If we use the sun as a gravitational lens telescope, we can get such an image of the planet Proxima Centauri.
The image above is the result of imaging the Earth at a distance similar to Proxima Centauri (24.4 light-years) with a telescope at 650 astronomical units from the Sun and using the Sun as a lens. A closer look at the image shows cloud cover and contrast between land masses (here in the United States and Baja California and Mexico). According to Toth and Toryshev estimates, the optimal exposure time to achieve such details is approximately one year.
Of course, researchers also identified project problems. For example, the distance to the focal area is the most important issue, which is exactly 28.82 billion kilometers from Earth. This is four times the distance between Earth and the Voyager 1 spacecraft, which holds the record for the farthest man-made spacecraft (150 astronomical units or 44.22 billion kilometers). In addition, lenses may have problems with distortion and astigmatism that need to be corrected. Eventually, the intense glare of the sun will definitely overwhelm the light of any other distant object. Tooth states:
Observations will take a long time; This is because the telescope can see one pixel by scrolling a one-kilometer plane in the focal region, and for each pixel it is necessary to collect enough data and reduce the effects of noise, especially solar corona noise. During imaging, the telescope’s motion relative to the image must be precisely defined, and the target planet may also move and change its appearance in terms of brightness (clouds, vegetation, etc.). Some of these problems can be considered as noise and others can be solved by the method of intelligent image reconstruction.
Fortunately, Toth and Turishev have suggested potential solutions to these problems. For example, in their conceptual research, they emphasize the use of a telescope with a 1-meter or 2 to 2.5-meter main mirror. This can be achieved by sending a small imaging spacecraft that can combine sharpness. To solve the problem of disturbing the sun, a kind of crown can be developed. Fortunately, based on estimates of the focal length of the sun, a corona with a diameter of one meter is sufficient. The development of this tool requires future developments.
In general, the three planets are within the habitable zone of TRAPPIST-1, all of which have the potential of surface oceans. To understand the nature of planets, we need valuable scientific data, such as spectroscopic data, to detect life-related chemical effects in the planet’s atmosphere. As a result, in the coming years, a dedicated SGL telescope could be developed that could be used alongside next-generation telescopes. Future missions include the James Webb Space Telescope (JWST) and the Nancy Grace Roman Space Telescope, developed based on the achievements of the Kepler and Hubble Telescopes, including the discovery of thousands of extrasolar planets in nearby systems.
Similarly, large terrestrial telescopes with adapted and coronary features, such as the ESO Large Telescope (ELT) and the Magellan Telescope (GMT), allow direct imaging of smaller rocky planets that are less distant from their own planet. Lighter M-type stars, or red dwarfs, are good candidates for habitable planets. Undoubtedly, SGL in the new age of astronomy and astronomy is worth exploring for purposes such as the discovery of extrasolar planets and the search for extraterrestrial life. In the end, Turishev says:
In the next 10 to 15 years, we will discover thousands of new extrasolar planets using indirect methods (transient spectroscopy, initial radial velocity, astronomy, microlens, etc.). SGL will help us explore these planets. We can also send spacecraft to the SGL focal area to investigate a predetermined target.