A team of researchers is publishing a paper based on new images captured by the Webb Space Telescope. The images reveal a dense concentration of matter in the early universe, which may indicate early stages in the formation of a galaxy cluster. Thanks to the existing spectrometer, Webb was able to confirm that many of the galaxies previously imaged by Hubble were also part of the cluster. It even tracked the flow of gas emitted from the largest galaxy in existence.
The main devices for this work are NIRSpec, and near infrared spectrometer This is part of the Webb Toolkit. Although the tool itself is quite advanced, it operates on important principles to operate things like your cell phone’s camera.
In these consumer cameras, sensors record the brightness of three different regions of the visible spectrum: red, green, and blue. The resulting images are created by combining this information, with different areas of the image having a distinct intensity for each of these colors.
The spectrophotometer also works by tracking the intensity of light in a limited region of the spectrum. The main difference is that the segments of the imaged spectrum are much smaller than the full range of color such as blue. And in this case, they are not part of the colors at all – all wavelengths are in the infrared region of the spectrum. However, just like RGB images produced by a camera, each part of the spectrum can either be analyzed individually or combined into an entire “color” image that includes a wide range of the spectrum.
Why is a spectrophotometer useful for looking at distant objects? There are two methods that were critical to this study. The first is that the light from the early universe turns red due to the expansion of the universe as it travels to Earth. So energetic photons with wavelengths such as ultraviolet are gradually stretched until they are recorded by Webb as infrared photons. Knowing exactly how much they are stretched tells us the distance to objects, and we need to know the current wavelength to determine that. The spectrometer provides this information.
The second major capability that the spectrometer provides is tracking of moving materials. All elements have a set of specific wavelengths at which light is emitted. But if they are in motion relative to an observer, that wavelength is either red – or blue due to the Doppler effect, changing the wavelength slightly (this effect would be in addition to the redshift caused by distance). So by identifying the emissions of a particular element and seeing how they shift, we can track the movement of those atoms, even over vast distances.
Active galaxy in a dense cluster
For the new work, Webb was directed to a so-called quasar, or active galactic core. It’s incredibly bright because of all the light produced as matter orbits around the supermassive black holes at the center of galaxies. In this case, the quasar, called J1652, was identified as very red in color, indicating that its light had changed strongly to red, and thus we would see it as it was in the early universe.
Webb’s imaging confirmed that the red color of J1652 was due to a large redshift; The redshift had a value of z ≈ 3, which means that the galaxy is seen as having existed more than 11 billion years ago. It is believed that this was a critical time in the evolution of the galaxy, when the massive energies emitted by supermassive black holes began to eject star-forming matter from the galaxy, putting an end to star formation.
Another striking result of the spectroscopy data is that at least three other objects detected in the same region in the Hubble images appear to have the same redshift. This means that they are additional galaxies in close proximity to J1652. Given that the entire imaged region spans 85,000 light-years, this represents a very high concentration of galaxies. (For comparison, the Milky Way is more than 100,000 light-years across, although it is much larger than these early galaxies.)
In addition to confirming distances, Webb’s data allowed the researchers to track ionized oxygen atoms, which are emitted at an appropriate wavelength. The red and blue shifts visible in these data show that the quasar is spewing material roughly toward Earth and in the opposite direction, consistent with the two jets that often form from black holes. The large amount of material ejected is also consistent with the idea that quasar formation could put an end to star formation by blasting the raw material away.
But the researchers seem more interested in the extremely high density of galaxies in the general region. Based on the amount of matter present, the researchers extrapolated the amount of dark matter and concluded that this is an area of the universe as dense as we have imagined so far, which they suggest is the product of the fusion of two different dark matter. auras;
arXiv file. Abstract number: 2210.10074 (About arXiv). For publication in Astrophysical Journal Letters.
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