Can We Build A Cosmic Telescope With Gravitational Lenses?

Using the principles behind Einstein’s General Relativity, is it possible to create a space based telescope with virtually no Raleigh Criterion limits?

By: Ringo Bones

I’ve first heard of the working principle of a cosmic telescope was in an episode of Cosmos: Possible Worlds where Prof. Neil DeGrasse Tyson explains how a space-based telescope using existing – i.e. late 20^th century to early 21^st Century technology - could take advantage of the Sun’s gravitational lensing effect in order to create a telescope capable of seeing the surfaces of extrasolar planets better than the ones we currently use like the Kepler Space Telescope. But first, here’s a brief primer on the principles of gravitational lensing.

The Gravitational lensing effect is a consequence of Einstein’s General Relativity. Often referred by astronomers as a “natural telescope”, gravitational lensing occurs when a huge amount of matter – such as clusters of galaxies – creates a gravitational field that distorts and magnifies the light from distant galaxies that are behind it, but in the same line of sight. The effect allows astronomers to study the details of early galaxies too far away to be seen with current technology and telescope. The gravitational lensing cause by our Sun’s gravitational field can also be used in a similar fashion. You can also spot distant extra-solar planets when a star itself is the interloper if it carries any planets in orbit around it, they will change - ever so slightly – the momentary brightness during the microlensing event.

There are already plans for a “viable” cosmic telescope that could – in theory – make the Raleigh Criterion limitations of the telescopes we currently use, space based or earthbound, completely irrelevant. The Fast Outgoing Cyclopean Astronomical Lens – or FOCAL – is a proposed space telescope that would use our Sun as a gravity lens. The concept of a space-based telescope that takes advantage of the Sun’s gravitational lensing effect was first suggested by Prof. Von Eshleman and analyzed further by Italian astronomer Claudio Maccone and others. In order to use the Sun as a gravitational lens, it would be necessary to position our space telescope to a point in space of at least 550 astronomical units away from the Sun.

The proposed FOCAL telescope can actually use current technology that’s already in use on operational space-based telescopes for astronomical use, however, there are difficulties. The Voyager 1 and Voyager 2 probes are currently at distances within 147 astronomical units and 122 astronomical units. It took them over 40 years to reach those distances using rocket technology we currently have – by the way, both Voyager spacecraft were launched back in 1977. It looks like we won’t be sending space telescopes with comparable technology to the James Webb Space Telescope to a point in space 550 astronomical units – or 51 billion miles or 82.5 billion kilometers– away from our Sun. By way of comparison, the dwarf planet Pluto is “only” 3.7 billion miles or 5.97 billion kilometers away from the Sun.