[비즈한국] James Webb looked at the ‘spirit’. This eerie place is the beautiful spiral galaxy M74. It lies about 32 million light years away towards the constellation of Pisces. It is also known as the ‘Phantom Galaxy’. Subtly, as seen from Earth, the galactic disk is perfectly pointed straight ahead. Thanks to this, the beautifully coiled spiral arms from the center of the galaxy to the periphery are clearly visible.
Since ancient times, this galaxy has been a popular destination for astronomers. I looked at this place through various telescopes, including the Hubble Telescope. James Webb also captured this place with infrared light with a longer wavelength than previous observations. The tepidly heated dust filaments were more clearly revealed. And it was possible to trace the traces of recent star formation. The results were astounding. He captured unexpected features in the center of the galaxy, as well as intricate spiral arms and filaments of dust. in
The galactic center where you thought a supermassive black hole might be hiding is empty. Only the center of the galaxy is clean and clear of gas dust clouds. As if someone had deliberately cleaned it. What’s more, in that empty hole, the stars are full and shining! Clusters of stars are gathered at the heart of galaxies where it was thought that only black holes existed. What the hell is going on inside the spirit’s heart?
James Webb tells the story behind the heart of the ghost galaxy M74.
It is often thought that only supermassive black holes exist at the center of galaxies, but this is not true. In the case of dwarf and light galaxies, instead of a black hole at their center, there may be a cluster full of stars. Clusters of stars gathered in the center of the galaxy are called Nuclear Star Clusters (NSCs). It is still a mystery how stars can gather in such high densities and shine in the center of galaxies.
There are two most likely theories. One is that clusters that were massed outside the galactic center then slowly moved into the galactic center. This is called the cluster migration hypothesis. The other is that the star cluster was born here as the gas that initially gathered in the center of the galaxy was directly kneaded. This is called in-situ theory.
Interestingly, the more massive the galaxy and the larger the central black hole, the less visible the galactic nucleus cluster. At the center of massive galaxies, there are no nuclear clusters, only supermassive black holes. Because of this, some astronomers suspect that galactic core clusters are gradually collapsing into supermassive black holes over time. It is also thought that still undiscovered intermediate mass black holes may be hidden in the core cluster. (Galaxies rarely have a nuclear cluster and a supermassive black hole at their center. Surprisingly, our own galaxy does!)
In July 2022, James Webb looked into the center of the spiral galaxy M74. There, they found a large, rectangular, empty hole. Its size is about 650 light years × 1300 light years. Astronomers have calculated the total mass of the luminous nucleus cluster it contains. The total mass of the cluster is about 10 million times the mass of the Sun, which corresponds to the total mass of the nuclear clusters found in the center of our galaxy.
As explained earlier, the more massive the galaxy itself, the more difficult it is to find a nucleus cluster at its centre. In fact, comparing the total mass of various galaxies to the mass of their central clusters, the heavier the mass of the galaxy itself, the faster the mass of the nucleus decreases. Interestingly, the Milky Way and M74 lie at the lowest mass end of the nuclear cluster. This is probably because the two galaxies span the boundaries of a nuclear cluster in their centre.
Previously, the Hubble Telescope and this time James Webb analyzed the spectrum of starlight in the cluster in a wide range spanning ultraviolet, visible and infrared light. As a result, most of the stars in the cluster at the center of M74 are very old stars. It was born on average 8 billion years ago. The content of heavy elements was also found to be very high. This means that stars that have already completed evolution long ago exploded and left various elements in the space around them. The birth of new stars doesn’t seem to happen anymore. In order to create new stars, there must be a lot of gas dust to become material. However, there is no stardust in the center of the M74 galaxy. There is only an empty hole around the older stars that have already been massaged long ago and glow tepidly.
But astronomers have noticed strange signs here. There is no problem in ultraviolet rays, visible rays, and near-infrared rays with short wavelengths. However, only the mid-infrared, which has a longer wavelength, shone brighter. This is a light that cannot be explained by the older clusters of stars in the galactic center alone. Also, the position of the brightest part in the center of the galaxy on other wavelengths and the brightest part in the mid-infrared was out of alignment! The difference is a staggering 30 light years in distance. In other words, unlike other wavelengths, something that emits the most intense mid-infrared wavelengths of light exists 30 light years away from the center of the galaxy. How else can I explain this?
One possibility is that an unknown active black hole lurks at the center of the galaxy. When powerful X-ray energy is ejected from the central black hole, the energy is absorbed by the dust cloud surrounding the black hole. The lukewarm dust cloud can then emit light in the infrared region with longer wavelengths. However, the existence of a black hole at the center of M74 is still being debated.
Another possibility is that many star clusters stream into the galactic center from all sides. In particular, this theory is related to the fact that the most visible part is in the infrared region of the center of the galaxy about 30 light years away from the center of the galaxy. This may be due to the process of inflow of star clusters towards the centre. When the star cluster is pulled towards the center by the gravitational field of the entire galaxy, it rapidly spins inward. In this process, the cluster is crushed and the stars in the cluster are shattered. It can therefore give the illusion of appearing as stars surrounded by a thick layer of gas dust. Eventually, as the dust around the shattered cluster becomes lukewarm from the starlight, it can also emit more energy, especially in the infrared.
Unfortunately, this scenario is not perfect either. According to recent simulations, this influx of star clusters should end very quickly, in just over a million years. This is an extremely short time compared to the average age of 8 billion years for star clusters actually observed in the center of the M74 galaxy.
So, there is one last interesting theory to think about. Another background galaxy may coincidentally overlap in the exact same direction as the center of M74 and very far away. Already in other studies, other astronomers analyzed images of 1271 nearby galaxies using artificial intelligence algorithms, and also extracted data that suspected that another background galaxy accidentally overlapped behind them. Among the 115 candidates that came out, the M74 is also included.
We’re not sure yet, but interestingly enough, maybe if we could pierce the heart of this beautiful cosmic sight further, we might find another hidden background galaxy that happened to overlap in exactly the same direction.
Let’s look at the heart of the spirit again with this amazing discovery in mind. What do you see in that heart? A massive black hole still lurking undetected? Clusters of stars that flow rapidly to the center of the galaxy and disintegrate suffer? Or another, more distant galaxy lurking beyond? I don’t know the answer yet. But there will be a shocking end to any answer. Do not look at the picture for too long. You might lose your mind by falling for the spell of this truly haunted galaxy.
address
https://iopscience.iop.org/article/10.3847/2041-8213/aca53e
a writer Ungbae JiYes? I love cats and space. As a child, he watched ‘Galaxy Express 999’ and had a dream to publicize the beauty of the universe. Currently, he studies the evolution through the interaction of galaxies at Yonsei University’s Galactic Evolution Research Center and Near Cosmology Lab, and is involved in various scientific communication activities such as lectures and writing. He wrote books such as ‘Thumping Observatory’, ‘Thinking about the Universe All Day’, and ‘The Science of Stars and Light’. . .
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Science columnist Ji Woong-bae writer@bizhankook.com
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