The James Webb Space Telescope offers astronomers unprecedented new opportunities. It's also a timely opportunity to reflect on what previous generations of telescopes have shown us.
Astronomers rarely use their telescopes to simply take pictures. Pictures in astrophysics are often produced through processes of scientific reasoning and imagination, sometimes visualized in the artist's impression of the data.
Choosing a few pictures is not easy. I limit my choices to images produced by publicly funded telescopes that reveal some interesting science. I'm trying to avoid very popular images that are already widely viewed.
The choices below are personal, and I'm sure many readers can advocate for different choices.
1. The poles of Jupiter
The first image I chose was made by NASA's Juno mission, which is currently orbiting Jupiter. The image was taken in October 2017, when the spacecraft was 18,906 kilometers from Jupiter's cloud top. It captures the system of clouds in Earth's northern hemisphere and represents our first impression of Jupiter's poles (north pole).
The image on which the photograph is based reveals complex flow patterns, similar to cyclones in Earth's atmosphere, and striking effects caused by various clouds of varying heights, sometimes casting shadows on the clouds below.
I chose this photo because of its beauty and the surprise it produces: the part near the North Pole of the Earth looks very different from the part we saw near the equator before. By looking down at Jupiter's poles, Juno shows us a different perspective on a familiar planet.
2. Eagle Nebula
Astronomers can gain unique information by building telescopes that are sensitive to "color" light that we cannot see with the naked eye. The familiar rainbow is only a small part of what physicists call the electromagnetic spectrum.
Beyond the red is infrared, which carries less energy than optical light. Infrared cameras can see objects that are too cold to be detected by the human eye. In space, it can also see through the dust, otherwise it will completely obscure our view.
The James Webb Space Telescope will be the largest infrared observatory launched to date. So far, the European Space Agency's Herschel Space Observatory has been the largest. The next image I chose was a Herschel view of star formation in the Eagle Nebula (also known as M16).
Nebulae are clouds of gas in space. The Eagle Nebula is located 6,500 light-years from Earth, which is fairly close to astronomical standards. This nebula is an active star-forming site.
A close-up view of a feature near the center of the image is called the "Pillar of Creation". The columns look a bit like thumbs and indexes pointing up and slightly to the left, reaching into cavities in huge clouds of molecular gas and dust. Winds from vibrant new stars that have recently formed deep in the clouds are sweeping away this cavity.
3. Galaxy Center
This picture looks deeper into space at the center of our galaxy. It also uses infrared light, this time combining data from two NASA telescopes, Hubble and Spitzer.
The bright white area in the lower right corner of the image is the center of our Milky Way. It contains a massive black hole called Sagittarius A*, a cluster of stars, and the remains of a massive star that exploded into a supernova about 10,000 years ago.
Other clusters are also visible. The pentagram in the lower left corner of the image is located inside a bubble, and the star's wind has cleared the local gas and dust. In the upper left corner there is a cluster called an arch, which takes its name from the glowing arc of gas that extends above it and extends from the image. These two clusters include some of the most massive stars known.
4. Abel 370
At scales much larger than individual galaxies, the structure of the universe is made up of filaments (long chains of connections) of dark matter. Some of the most striking visible objects are galaxy clusters that form at the intersection of filaments.
If we look at nearby galaxy clusters (relatively, of course), we can see strong evidence that Einstein was correct in asserting that mass bends space. One of the prettiest examples of revealing this space warp can be seen in the Hubble Abel 370 image released in 2017.
Abell 370 is a cluster of hundreds of galaxies located about 5 billion light-years away. In the picture, you can see the elongated arc of light. These are magnified and distorted images of more distant galaxies. The mass of the cluster distorts space-time and bends the light coming from more distant objects, amplifying them, in some cases producing multiple images of the same distant galaxy. This phenomenon is called gravitational lensing because distorted space-time resembles an optical lens.
The most prominent of these enlarged images are the thickest bright arcs above and to the left of the center of the image. This arc is called "dragon", and its head and tail consist of two images of the same distant galaxy. Overlapping images of several other distant galaxies form the arc of the dragon's body.
These gravitationally magnified images are useful for astronomers because magnification shows more detail about long-range lens objects than other ways to see. In this case, the stellar swarms of the lenticular galaxy can be examined in detail.
5. Hubble Ultra Deep Field
Sometimes, less is more. NASA, ESA, and S. Beckwith (STScI) and HUDF teams, CC BY 4.0
In an inspired idea, astronomers decided to point Hubble at a blank patch of sky for a few days to discover which extremely distant objects might be seen at the edge of the observable universe.
Hubble's ultra-deep field contains nearly 10,000 objects, almost all of which are very distant galaxies. The light of some of these galaxies has been propagating for more than 13 billion years, because the universe is only about 5 billion years old.
Some of these objects are the oldest and most distant known objects. Here we see light from ancient stars whose native contemporaries have long since been extinguished.
The oldest galaxies formed during the reionization period, when the thin gas in the universe was first bathed in starlight capable of separating electrons from hydrogen. This is the last major change in the nature of the entire universe.
The fact that light carries so much information that allows us to piece together the history of the universe is remarkable. The launch of the James Webb Space Telescope will provide us with some greatly improved infrared images and will inevitably raise new questions to challenge future generations of scientists.
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