Gravity makes a Lens

James Webb Space Telescope Update: As of 5 days ago the JWST is continuing to complete set up functions that will make it the b_ _ a_ _ telescope it is designed to be.

It is orbiting within L2 (Lagrange point 2), where a gravitational equilibrium exists, and its sunshield is deployed.

The next steps include letting JWST naturally cool down to a frigid 15-20 degrees Kelvin (-432.7 degrees Fahrenheit, -258 degrees Celsius) and collimating its 18 mirror segments. As frigid as 15 degrees K is, to be fully functional JWST needs its Mid-infrared Instrument (MIRI) to operate at 7 degrees K, so an active cryogenic (cooling) system will be used to maintain MIRI’s temperature.

Three of seven steps to align JWST’s mirrors have been completed, see the included photo from NASA. Funny thing about optics, and windows for that matter – they do not work well when iced up! To prevent the optical components from icing, NASA has installed heaters. JWST is a complex beast!

Don’t hold your breath, it will be several months before JWST begins its leg of humankind’s exploration of our early universe, exo-planets, and more.

We have huge telescopes on Earth and the JWST is the biggest in space, but gravity can make a lens bigger than our galaxy! So, why don’t we just use those lenses? Short answer is we do, but limitations exist based on the gravity producing mass and our ability to interpret the result.

Several scientists proposed the phenomenon of gravitational lensing, starting with Newton, although his predictions were half of what is seen. In 1912 Einstein made calculations regarding this phenomenon but did not publish. In 1924 Russian physicist Orest Khvolson published his work on the subject and in 1936 Frantisek Link published his study. Later in 1936 Einstein published his article, and in 1937 Fritz Zwicky also joined the fray promoting the concept of gravitational lensing.

Gravitational lensing can be thought of as an extension of Einstein’s relativity theory, where his calculations predicted the bending of light as it passed by a massive object, like the Sun. This was supported by data from the total solar eclipse of 1919. A star’s apparent position was different from its known position due to the Sun’s mass (gravity) deflecting its light path.

On a much, much larger scale, a large galaxy or cluster of galaxies that are in front of an object can bend its light around, so it is revealed. What a trick! But the revealed object is distorted based on the galaxy’s or galaxy cluster’s mass and symmetry. And unlike corrected optical lenses, gravity lenses do not have a focus point because the effect drops off as distance from the center of mass increases. The images are stretched, curved, and often incomplete. Sometimes they from a ring of images, called an Einstein Ring.

What’s in the Sky?

March 8; 8 pm; southwest: A waxing crescent Moon is between red giant Aldebaran (Taurus) and the Pleiades.