Looking into the Past (Part 2)

  

James Webb Space Telescope

Welcome back, readers. If this is the first article you have opened, I’d highly recommend reading the first part of this article. While the former was about the engineering elements of JWST, this article is mostly focused on the physics surrounding JWST.

While discussing the parts of JWST, we talked about the Sun Shield. For the sun shield to successfully protect us from the heat of the Earth, Moon and Sun it should be placed 1.5 million kilometres from Earth. The telescope is placed at a point in space called Lagrange Point 2. It is one of the five Lagrange points.

The five Lagrange Points

Lagrange points are locations in space where both the Earth and the Sun exert a gravitational pull in the same direction. An object at this point has two gravitational forces pulling on it to make it move in a circle. This not only allows it to orbit the sun with a higher velocity, but it also keeps it at a fixed point relative to our planet. The JWST orbits the sun instead of the Earth. We want the JWST to be both further from the sun and complete a solar orbit in the same amount of time as the Earth? To make it easier to control, the telescope would also have to remain in the same position relative to the Earth. Here, the Lagrange point comes into the picture.

Why Infrared?

A question that keeps appearing, again and again, is why we have chosen infrared as our desirable wavelength for detection?

Infrared waves have a longer wavelength than visible light. It means it can easily penetrate dust clouds and we can observe more far-off objects. Moreover, the light of galaxies that are billions of light years away from us travels to us through an ever-expanding space. This stretches the wavelength of visible light into the infrared region. Near-infrared light reveals the formation of galaxies and due to its longer wavelength, it can pass through the dust layers that enclose the newborn stars. Mid-infrared light peers through the cold, dusty regions where stars form, and reveals how massive stars and black holes shape their surroundings.

Southern Ring Nebulae in Near and Mid-Infrared Regions

Moreover, various types of celestial objects – including the planets of the solar system, stars, nebulae, and galaxies give off energy at wavelengths in the infrared region of the electromagnetic spectrum.

A follow-up question that comes to mind is if we are so adamant about looking at the Universe’s past. Why not take it to extremes and study light in microwave regions? As far as we know the Cosmic Background Radiation is in the Microwave region. Won’t it enable us to look further into the past, right to the origins of the Universe?

Well, the answer is yes and no. This means it is a little complicated…

Infrared and microwave imaging both have their own advantages and are useful for different purposes in astronomy. Infrared imaging is preferred over microwave imaging in many cases because it provides higher spatial resolution and can reveal more details about the characteristics of astronomical bodies. Infrared radiation has shorter wavelengths than microwaves, which means it can be used to study smaller features in the Universe. In addition, infrared radiation is absorbed and emitted by many astronomical objects, which makes it useful for studying the temperatures and compositions of these objects. Spatial resolution is inversely proportional to the observing wavelength. The higher the wavelength, the lesser would be its resolution and vice-versa.

Different Spatial Resolutions

Microwave imaging is preferred in some cases because it can penetrate through clouds of gas and dust that may obscure infrared radiation. Microwaves are also less affected by atmospheric turbulence, which can distort images taken at other wavelengths. This makes them useful for studying objects behind dense clouds of gas and dust, such as the centres of the galaxies. Microwave imaging is also useful for studying the cosmic microwave background (CMB), which is the leftover radiation from the Big Bang.

Cosmic Microwave Background

In summary, both infrared and microwave imaging have their own advantages and are used for different purposes in astronomy. Infrared imaging is preferred due to its higher spatial resolution and ability to reveal details about astronomical objects, while microwave imaging is useful for studying objects behind dense clouds of gas and dust and for studying cosmic microwave background radiation.

The Sun in different wavelengths

The next order of business is asking what makes Webb different from Hubble. In what ways is Webb an upgrade or a downgrade in comparison to Hubble?

Both JWST and Hubble are reflecting telescopes that conceptually work the same. Light reflects off a large primary mirror onto a secondary mirror, which sends it back through a hole in the primary mirror and into science instruments for analysis.

The basic difference between the two telescopes is the wavelengths they work at. Hubble, which is in Earth's orbit, is optimized for visible and ultraviolet wavelengths of light. 

Karina Nebulae as seen from Hubble and Webb

Webb essentially orbits the sun and is situated at Lagrange point 2 which is 1.5 Million Kilometres away from Earth as opposed to Hubble which is 535 Kilometers. This makes maintenance work on Hubble easier than it is for Webb.

Distance of Hubble and Webb from Earth

Hubble’s single mirror is 2.4 meters (7.9 feet) wide, whereas JWST’s segmented honeycomb-shaped mirror is 6.6 meters (21.7 feet) across. JWST has the largest mirror ever flown in space. Tiny actuators shape each mirror to provide a single, sharp image for the telescope’s science instruments to digest. Even though Webb’s mirror is a lot bigger in size and a hundred times more powerful, it is still 113 Kilograms lighter than Hubble’s mirror.

Hubble vs JWST Primary Mirror

The two telescopes also have very different cooling requirements. Hubble does not have as sophisticated cooling needs as JWST.

How has Webb changed and challenged our understanding of Physics?

A picture that made big news two months back was captured by Webb. It showed multiple galaxies that were formed way before our current understanding of Physics would permit. These galaxies grew way too large way too soon after the big bang. News spread everywhere. Webb has broken the Big Bang theory. So, do these pictures put our current understanding of the Big Bang and the Standard Model into question?

The oldest galaxies captured by James Webb

As fascinating as it might be, the answer is no. Recently, researchers took a closer look at the data and concluded that the distant galaxies discovered by Webb are in fact in perfect compatibility with our modern understanding of Cosmology.

As things go this might not even be the final answer and astronomers may find galaxies at very large distances with very large masses that puts our understanding of Physics into question.

But, we must always remember that in science, it’s always important to keep an open mind. For now, we can keep the exaggerated claims to rest.

I hope you liked this article and enjoyed reading it as much as I enjoyed writing it. Goodbye for now.

Auf Wiedersehen!