A physicist at NASA’s Jet Propulsion Laboratory has calculated how to use the Sun’s gravity to obtain images of white dwarfs and black holes with a precision unattainable by any modern telescope. The new study proposes using the Sun’s gravitational lens not only to image exoplanets, but also for entirely different astronomical purposes.
How a solar lens works
The concept of a solar gravitational lens (SGL) is based on predictions from the general theory of relativity. The Sun’s mass warps the space around it, causing light rays from distant objects to bend and focus along a line that begins approximately 550 astronomical units from our star.
An instrument equipped with a meter-class telescope positioned along this focal line could reconstruct images of Earth-like exoplanets at distances of up to several tens of light-years, with details down to tens of kilometers. Until now, exoplanets have been considered the primary target of SGL.
Not just exoplanets
According to Phys.org , physicist Slava Turyshev of NASA’s Jet Propulsion Laboratory focused on objects that emit their own light in a preprint posted on arXiv. For exoplanets, the main obstacle is a lack of photons, since a telescope must collect the signal for a long time to distinguish it from the background noise of the solar corona.
For bright, compact objects, the math is radically different. The key factors become navigation along the focal line, the detector’s dynamic range, and the removal of background light from the corona. Slava Turyshev calculated three scenarios in detail.
White dwarf in detail
The first example concerns the surface of a magnetic white dwarf. These compact stellar remnants are similar in size to Earth but have an extremely high luminosity.
Modern instruments can distinguish details on a surface only with an accuracy of micro-arcseconds—that is, millionths of an arcsecond. According to Slava Turyshev’s calculations, the SGL will be able to reconstruct the surface of a white dwarf 10 parsecs away with an accuracy of nano-arcseconds—that is, one-billionth of an arcsecond—making temperature gradients and rocky debris in the accretion disk visible.
Orders of magnitude better than the Event Horizon Telescope
The second scenario concerns the supermassive black hole M87*. The first image of this object, obtained using the Event Horizon Telescope (EHT) in 2019, had a resolution of about 20 microarcseconds. Slava Turyshev demonstrated that SGL is capable of achieving 0.66 microarcseconds per pixel—an improvement by several orders of magnitude.
Even recent EHT test observations at 345 GHz reached only 19 microarcseconds, which is already the limit of what ground-based interferometers can achieve. The third scenario involves detailed imaging of specific regions of protoplanetary disks, such as zones of active planet formation.
Engineering complexity of the mission
The main engineering challenge lies not in the optics, but in navigation. To point the lens at another object in the sky, the spacecraft must physically change its position at a distance of 650 AU from the Sun. Even shifting the field of view by a single degree requires a displacement greater than the distance from Earth to Saturn.
The article’s findings have not yet undergone formal peer review. At the same time, the SGL concept has already been selected three times for funding under NASA’s NIAC (New Ideas for Advanced Concepts) program, and solar sails capable of providing speeds of up to 150 km/s during a flyby of the Sun are being considered to accelerate the spacecraft.
