New Webb images shed light on galaxy cluster formation

New Webb images shed light on galaxy cluster formation

The separation of different wavelengths of light allows us to track the movement of matter towards and away from Earth.
Enlarge / The separation of different wavelengths of light allows us to track the movement of matter towards and away from Earth.

A team of researchers publishes an article based on new images taken by the Webb Space Telescope. The images reveal a dense concentration of matter in the early Universe, potentially indicating the early stages of galaxy cluster formation. And thanks to the spectrograph present, Webb was able to confirm that several galaxies previously imaged by Hubble were also part of the cluster. It even tracked the flow of gas ejected by the largest galaxy present.

Graphic representation of the spectrum

Key hardware for this work is NIRSpec, the near-infrared spectrograph that is part of Webb’s instrument set. Although the instrument itself is very sophisticated, it operates on principles important to the operation of things like your cell phone camera.

In these consumer cameras, sensors record the brightness of three different areas of the visible spectrum: red, green and blue. The resulting images are made by combining this information, with different areas of the image having distinct intensities of each of these colors.

A spectrograph also works by tracking light intensity in a limited area of ​​the spectrum. The main difference is that the spectrum slices imaged are much smaller than the full range of a color like blue. And in this case, they are not part of the colors at all – all wavelengths are in the infrared region of the spectrum. Yet, just like the RGB images produced by a camera, each piece of the spectrum can be analyzed individually or combined into a complete “color” image that includes a wide range of the spectrum.

Why is a spectrograph useful for observing distant objects? There are two ways he was essential to this study. The first is that light from the early Universe is redshifted by the expansion of the Universe as it travels towards Earth. Thus, energetic photons at wavelengths like UV are gradually stretched until they are registered by Webb as infrared photons. Knowing exactly how stretched they are tells us the distance to objects, and we need to know their current wavelength to determine that. A spectrograph provides this information.

The second key capability provided by a spectrograph is the tracking of materials in motion. All elements have a set of specific wavelengths at which they emit light. But if they are in motion with respect to an observer, then this wavelength is shifted towards red or towards blue by the Doppler effect, modifying the wavelength slightly (this effect will be added to the shift towards the red caused by the distance). So, by identifying the emissions of a specific element and seeing how they move, we can track the movement of those atoms, even at great distances.

An active galaxy in a dense cluster

For the new work, Webb was pointed at what’s called a quasar, or active galactic nucleus. These are incredibly bright due to all the light produced as matter swirls around supermassive black holes found at the center of galaxies. In this case, the quasar, called J1652, had been identified as being very red in color, suggesting that its light had been strongly red-shifted and therefore we saw it as it was in the early Universe.

Webb imaging confirmed that the red color of J1652 was due to a large redshift; the redshift had a value of z ≈ 3, meaning the galaxy is seen as it existed over 11 billion years ago. It is thought to be a critical moment in the evolution of galaxies, when the enormous energies released by their supermassive black holes began to flush star-forming material out of the galaxy, putting a limit on the formation of stars. stars.

Another striking result from the spectrographic data is that at least three other objects that had been detected in the same area in the Hubble images turned out to have the same redshift. This means that these are additional galaxies close to J1652. Since the entire imaged area is 85,000 light-years in diameter, this is a very high concentration of galaxies. (For comparison, the Milky Way is over 100,000 light-years in diameter, though it is significantly larger than those early galaxies.)

In addition to confirming distances, the Webb data allowed the researchers to track ionized oxygen atoms, which emit at a convenient wavelength. The red and blue shifts apparent in this data show that the quasar is ejecting material both approximately towards Earth and in the opposite direction, consistent with the two jets that are often formed by black holes. The large amount of ejected material is also consistent with the idea that quasar formation can limit star formation by blowing up raw material.

But the researchers seem more interested in the extremely high density of galaxies in the general area. Based on the amount of matter present, the researchers deduce the amount of dark matter and conclude that this is an area of ​​the Universe about as dense as we have imagined so far. , which they believe is the product of a fusion of two different dark materials. halos.

The arXiv. Abstract number: 2210.10074 (About arXiv). To appear in The Astrophysical Journal Letters.

#Webb #images #shed #light #galaxy #cluster #formation

Leave a Comment

Your email address will not be published. Required fields are marked *