Why is this photo worth 10 billion?

On July 11, 2022, the first color picture of the James Webb Space Telescope (JWST) was officially released , and it immediately became the most familiar starry sky photo for netizens around the world.

But the question is, why does this photo look so messy - what exactly is being photographed here?

In fact, this picture depicts a galaxy cluster called SMACS 0723.3-7327 , which is 6.9 billion light-years away. This picture is full of interesting details and can be regarded as an important and landmark work of art.

If we take the same enthusiasm as we appreciate the immortal masterpiece "Along the River During the Qingming Festival" to carefully appreciate this "Minor Heat Sky Picture " released after the Minor Heat solar term, we can also see interesting details and immerse ourselves in it.

01

"Shallow Arc"

Let’s start with some less noticeable places. The “Minor Heat Sky Map” has many colorful highlights, but there are also wonderful details in relatively dim places.

In Figure 1, you can see some faint arcs. Although they are "faint", they are the masterpieces of the gravitational lensing effect produced by galaxy clusters, just like the most amazing huge gravitational arcs in the photo .

Figure 1

You may have heard that according to the general theory of relativity, gravity can bend light. In the middle of the "Minor Heat Sky Map" is the central region of the SMACS 0723.3-7327 galaxy cluster. The significant gravitational effect brought by the huge mass of the galaxy cluster deflects some of the electromagnetic waves that pass through this area and shoot towards us , creating these shallow arcs.

The amazing gravitational effects that bend light are not primarily caused by the bright galaxies you see in the photo. In fact, galaxy clusters are located in huge invisible collections of matter that astronomers call "dark matter halos," which are much larger than the entire photo. Mapping the distribution of this dark matter is also one of the important tasks of astronomers.

To astronomers, those curved lines are like koi carps swimming slowly in a pond, and dark matter is the water. We cannot see the clear water, but we know that the water is between the koi carps - and every koi carp helps astronomers understand the dark universe better.

02

"Distorted galaxies"

The curved structure in Figure 2 is the most eye-catching thing in the "Less Heat Sky Picture".

The gravitational lensing effect of dark matter mentioned above can shape background galaxies into various unique shapes. The distorted spiral galaxy on the left of Figure 2 looks a lot like the distorted clock in Dali's famous work "Melting Clock".

Figure 2

However, what is more interesting is the scientific details. The two distorted galaxies marked in orange in Figure 2 seem to be trying their best to avoid colliding with the white galaxies next to them. This "distorted" posture is also related to dark matter.

Around those white galaxies, there are also "sub-halos" that dominate their respective destinies. These structures, which are smaller than the dark matter halos of galaxy clusters, force the light from the orange galaxies to "go around", forming a distorted appearance. Such structures allow astronomers to see the "clumps" within the dark matter halos of galaxy clusters . The gradual reduction of the observation scale can also help us get closer to the answer to the question of "what is dark matter".

03

“Pearl-like highlights”

The area in Figure 3 is very small, but if you zoom in, you can see some pearl-like bright spots scattered around the galaxy. These pearls are actually a series of young star clusters that were born in galaxies in the early universe .

Figure 3

Previously, astronomers did not have good conditions to directly observe these "pearls", but now they can also study in detail the formation of stars in distant galaxies.

In addition, similar to the previous "koi", each "pearl" provides an additional signpost for mapping dark matter . Their precise location can tell astronomers how dark matter is distributed on a scale smaller than a single galaxy? Is there a more detailed structure? These questions have puzzled astronomers for a long time.

04

"Symmetrical Galaxy"

If you were able to zoom in on the area in Figure 4 and look closely, you might notice that the galaxy appears to be bilaterally symmetrical.

Figure 4

I have marked the axis of symmetry with a dotted line on the enlarged image. Look, are the bright spots pointed out by the arrows on both sides of this axis of symmetry completely symmetrical?

This symmetrical pattern is not the true appearance of this galaxy. In fact, it is because it is located at a specific position in the mass distribution of the "gravitational lens" that a special "folded light arc" is formed .

05

"Cinnabar Dots"

The two areas in Figure 5 each have a little bright red dot, which is as beautiful as a little cinnabar. I need to remind you again that the wavelength of this photo is not within the visible light range, and all the colors in the picture are the result of post-production coloring by the production staff .

Figure 5

However, the colors filled in still have physical significance. The two "cinnabar dots" are the dream targets of many astronomers: the bright red color means that their radiation is all concentrated in the infrared band with the longest wavelength, which is exactly the typical observational feature of galaxies in the very early universe .

They were born in the "infant universe" that was only 100 million to 200 million years old and are extremely far away from the earth, so their light is extremely dim - they can only be seen with the help of a cosmic magnifying glass such as a galaxy cluster.

06

Elliptical galaxy

Now, let's look at the center of this photo. Figure 6 shows the most prominent galaxy in the entire photo: the elliptical galaxy sitting in the center of the galaxy cluster. They are the most massive and rare galaxies in the universe, reaching up to one trillion times the mass of the sun .

Figure 6

Beneath their creamy, gentle colors and calm appearance, there is an endless battle of survival between galaxies for more than 10 billion years. Frequent and repeated galaxy mergers eventually created this behemoth.

If you look more carefully, you may also notice the faint stars that appear and disappear under the silky light of the galaxy . They are actually globular clusters, which are star systems that can only form under unique conditions in ancient times and are witnesses of the violent star formation activities in the past. Today, the star formation activities in the galaxy have completely extinguished, and only the globular clusters all over the ground are still telling of the glory of the past.

In fact, in this seemingly "chaotic" "Minor Heat Sky Map" by JWST, astronomers can find at least 10,000 star clusters as shown in Figure 6. This shows the grand and enthusiastic scene during the birth of the universe.

07

"Floating Jellyfish"

Figure 7 looks like a jellyfish floating in the dark space. The galaxy in the lower right corner looks like the head of the jellyfish, while the diffuse flocculent structure in the upper left corner looks like the tentacles of the jellyfish.

Figure 7

At first glance, the elegant and beautiful "jellyfish" actually reflects the extremely cruel side of galaxy clusters: the high-temperature plasma gradually strips away the gas in the galaxy, and the drifting gas eventually forms a structure that looks like the tentacles of a jellyfish. This process is called " ram pressure stripping ."

You can demonstrate its effect yourself: imagine running with a stack of newspapers in a windless gymnasium. The oncoming air currents tear the newspapers apart and throw them away. This is because the speed of running causes the air molecules to exert enough pressure on the newspapers to overcome the weight and friction. Similar processes are constantly happening in galaxy clusters.

08

"Whirlpool Galaxy"

There are so many wonderful things in this "Minor Heat Sky Map" that the "normal" galaxies don't show any special features and are easily overlooked.

But when you look at them, you will find that each galaxy has its own unique character, just like the many vivid characters in the painting Along the River During the Qingming Festival. Among them, the most numerous are the different types of spiral galaxies shown in Figure 8.

Figure 8

Their spiral arms are either stretched out, or unrestrained, or twisted due to tension, depicting the vigorous vitality of the galaxy ecosystem. As an astronomer, I always feel very close to spiral galaxies, because the cosmic island we are in is just such an ordinary-looking spiral galaxy .

09

"A vague 'shadow'"

Even less noticeable than the spiral galaxy in Figure 8 are the fuzzy "shadows" in Figure 9.

Fig. 9

These shadows are called " low-brightness galaxies ." They are so dim because the stars inside them are so sparsely distributed. They are very difficult to see - even with JWST, the most powerful space telescope ever built.

However, in recent years, astronomers have realized that these guys are indispensable to galaxy clusters. Their unique appearance is likely due to the special properties of the dark matter halo that gave rise to them or some special physical processes . At present, astronomers know very little about these shadows, but they must contain huge scientific potential.

In fact, there are many unknown objects in the low-brightness area of ​​the image. For example, the "fang-baring claw" structure on the far right of Figure 9 has puzzled many experienced astronomers.

Is this an extremely extended galaxy distorted by gravitational lensing? Or is it the remains of a galaxy in the process of disintegration? No one knows why yet, and as observations deepen, more and more similar mysteries will emerge.

10

"Intercluster Light"

Figure 10 shows the largest low-brightness structure in the original image of the "Minor Heat Sky Map". It can be said to be the least noticeable area. However, when we use the image beautification tool and increase the contrast, we can see two fuzzy lights at the two ends of the galaxy .

Fig.10

Don't doubt your eyes, this is real " intercluster light ", a witness to the history of the construction of galaxy clusters. Whenever a galaxy falls into a galaxy cluster, in the process of being disintegrated and swallowed, some stars will be stripped out and wander between galaxies.

After countless mergers, these "wandering ghosts" can also accumulate enough mass. The fuzzy "intercluster light" symbolizes the boundary between the light and dark worlds. They are not only important clues to the history of galaxy cluster assembly, but also signposts for astronomers to depict the distribution of dark matter.

In this "Minor Heat Sky Map", astronomers can identify tens of thousands of celestial bodies. The 10 details above are just a few words in the grand cosmic epic told by this picture. But I believe you can already feel the huge potential of this most powerful space telescope in human history.

As an "artist" facing the public, JWST's first work "Minor Heat Sky Picture" is so amazing. How amazing will his more mature works be in the future? Let's wait and see.

Author｜Dr. Bald Monster

Review｜Liu Qian, Researcher at Beijing Planetarium