The science of observing not the present, but the past
The image shared by the president of the American Union contains galaxies from different times in the history of the universe. For example, the galaxy cluster at the center produced its light 4.6 billion years ago. This means that the light captured took that long to reach Earth, which is why it is often said that astronomy is always looking at the past.
“The light that comes out of any object in space has to travel to get to Earth. For example, light from the Moon takes a little over a second to reach us; that of the Sun takes eight minutes; that of the nearest star (Proxima Centauri) takes four years. So in those cases we see the Moon, the Sun and Proxima Centauri as they were just over a second, eight minutes and four years ago, respectively”, says Lorena Arias.
Ávila-Reese also affirms that some stars, which are close to our own Milky Way, slipped into the image. These are point objects and produce an optical effect called diffraction spikes on the telescope lens.
“That explains the spikes coming out of the stars. Astronomers typically mask these stars with image processing techniques so they don’t contaminate the faint and valuable light coming from distant galaxies.”
On July 12, the US space agency (NASA) released other images obtained by the James Webb Space Telescope. And they confirm the same as the first image: the superiority to see astronomical objects with much more detail.
This is because James Webb has the ability to perceive light in the near, mid, and far infrared, while Hubble sees only in the near and optical infrared.
“When we say optical or visible light, we mean what we can see with our eyes. Visible light is only found in one region, the smallest of all, of something very large called the electromagnetic spectrum, which contains microwaves, radio waves, infrared, ultraviolet, among other waves”, explains Martínez Gordillo.
The James Webb has such a high sensitivity that, according to Ávila-Reese, it could measure the temperature of an insect on the Moon from Earth.
On the other hand, Lorena Arias points out that the Hubble has a diameter of two meters, while the James Webb has a diameter of six and a half meters to capture light, for which the second of them has a greater capacity to detect celestial bodies .
However, the new telescope also has its limitations. There are two regions of the universe that it will not be able to detect, as explained below by Alejandro Cristian Raga Rasmussen, a researcher at the Institute of Nuclear Sciences of the UNAM.
“You will not be able to see very distant areas, beyond the current horizon of the universe (it is from where the radiation produced in the Big Bang is just reaching us). This region of the universe is in principle not observable (by any instrument).
Nor will it be possible to detect the interior of very dense molecular clouds, within which many of the stars form. These areas have a lot of interstellar dust (similar to soot from truck exhaust) through which nothing can be seen at optical or infrared wavelengths. These dusty areas are transparent only to radio waves.”