Shulou(Shulou.com)11/24 Report--

On the morning of August 17, Beijing time, it is reported that after years of anticipation, NASA's James Webb Space Telescope (JWST) was finally launched on December 25, 2021. Over the next six months, the world's most advanced new generation of space telescopes unfolded sunshades, deployed primary and secondary mirrors, and adjusted the mirrors to reach the current space position, Earth-Sun Lagrangian 2 o'clock (L2). On July 12, 2022, the first images taken by the telescope were released, showing the most detailed image of the universe to date. Soon after, NASA released an image of the farthest galaxy ever observed, which is very old. Formed 300 million years after the Big Bang.

Using survey data from James Weber's near-infrared camera (NIRCam), the team obtained mass assessments of some distant galaxies, many times more accurate than previous measurements.

According to a new study by an international team of scientists, the James Webb Space Telescope allows astronomers to obtain accurate mass measurements of early galaxies. Using survey data from the James Webb near Infrared camera (NIRCam), the team obtained mass assessments of some distant galaxies, many times more accurate than previous measurements. The discovery means that the James Webb Space Telescope could revolutionize the traditional perception of the growth and evolution of the earliest galaxies in the universe.

It is reported that the international research team (headed by the Rome Astronomical Observatory Paola Santini (Paola Santini)) has senior experts from all over the world. Members come from: national Astrophysical Institute of Italy (INAF), ASTRO 3D Cooperation Organization of Australia, National Astronomical Research Institute of Thailand (ARIT), Cafley Particle Astrophysics and Cosmos Institute (KIPAC), Dawn Center of the Universe (DAWN), Niels Bohr Institute, Carnegie Institute of Science, California Institute of Technology Infrared processing and Analysis Center, United States, Europe, University institutions and research institutes in Australia and Asia.

As scientists have pointed out in their research, stellar mass is one of the most important physical properties to understand the formation and evolution of galaxies. James Webb Space Telescope can measure the total mass of stars in galaxies. The total mass of stars is constantly increasing through the conversion of gas and dust into new stars, so this is the most direct means to track and analyze the growth of galaxies. By comparing observations of the oldest galaxies in the universe, astronomers can study and analyze how galaxies evolve.

This picture is a spectral map that compares the light emitted by celestial bodies with the redshifted light observed. During the expansion of the universe, light extends to the lower frequency or the red part of the spectrum.

Unfortunately, obtaining accurate measurements of early galaxies has always been a thorny problem for astrophysicists. Usually, astronomers make mass-to-light ratio measurements (M / L) and use the light generated by galaxies to evaluate the total mass of stars in the galaxy. Instead of calculating star mass on a source-to-source basis. So far, the Hubble Space Telescope's survey of the farthest galaxies in the universe has been limited to the ultraviolet spectrum, such as the GN-z11 galaxy, which was formed 13.5 billion years ago, is a high redshift galaxy discovered in the constellation Ursa Major, and is the oldest and farthest known galaxy in the observable universe.

Since light from these ancient galaxies has a significant redshift when it reaches Earth, it means that when light passes through space-time, due to the expansion of the universe, the wavelength of light becomes longer, effectively causing it to move towards the red end of the spectrum. For galaxies with a redshift (z) of 7 or more (13.46 light-years or more), most of the light will be moved to the visible part of the infrared spectrum. As Santini explained via email to the Universe Today website:

"most stars in galaxies, especially those with larger masses, emit near-infrared wavelengths (NIR). The time it takes for distant galaxies to travel to our telescope, the light emitted by their stars is not just a matter of optics. For example, for galaxies with a redshift value of zodi7, when light at a wavelength of 0.6 microns is initially released to our telescope, the wavelength will reach 4.8 microns, and the higher the redshift (that is, the farther away the galaxy is), the more obvious this effect will be. "

This means that we need infrared detectors to measure the mass of stars in galaxies (most stars emit light that cannot be seen by the Hubble Space Telescope). Before the James Webb Space Telescope, the only infrared telescope we used was the Spitzer Space Telescope, but it was abandoned years ago. However, the 85-centimeter mirror of the Spitzer Space Telescope cannot be compared with the 6.5-meter mirror of the James Webb Space Telescope, and most distant galaxies are not within the scope of the Spitzer Telescope. Because of its limited sensitivity and angular resolution, distant galaxies cannot be detected and are vulnerable to high levels of cosmic background noise.

In addition, previous cosmic surveys are likely to have missed a large portion of red galaxies, which are rich in dust (which can blur light) and are weak in the ultraviolet spectrum, so previous estimates of the mass density of stars in the early universe would have been six times the error. But based on advanced infrared reconnaissance equipment and unparalleled sensitivity, the James Webb Space Telescope will open a "new window" to study the oldest and weakest galaxies in the universe. Santini pointed out that the James Webb Space Telescope will accurately measure the mass of the farthest galaxies for the first time.

Due to certain limitations in measuring stellar mass, one of the most commonly used methods used by astronomers before the launch of the James Webb Space Telescope was by assuming the ratio of average mass to ultraviolet light. Transfer the ultraviolet data that can be measured by the Hubble Space Telescope to the star mass assessment value. This mass-light ratio relationship is calibrated based on a small number of uncertain measurements and represents only those galaxy clusters that are easier to observe (young, dust-free galaxies). Therefore, there is great uncertainty in stellar mass measurement, whether it is direct measurement or inference of stellar mass by ultraviolet light.

In their research, Santini and her international research team relied on survey data from the James Weber Space Telescope near Infrared camera (NIRCam) to obtain the first set of space survey images on June 28-29, 2022, after which they detected ultraviolet radiation and redshift data (redshifts ranging from 6.7 to 12.3) in 21 distant galaxies, Santini stressed. The James Webb Space Telescope significantly improves the observation effect, avoids the inference and uncertainty in previous observations, and can improve the measurement accuracy by 5-10 times.

"by comparing constant mass with ultraviolet light (measured in the bluest NIRCam band), we find that the mass-to-light ratio measurement (M / L) is far less than a single average, on the contrary, it spans about two orders of magnitude for a given luminosity," she said. "from a physical point of view, the findings show that the early galaxy population was largely heterogeneous and that galaxies showed a variety of actual conditions."

"this is only part of a growing number of astronomical studies in recent years, but these studies show that the James Weber mission is critical, which can provide more rigorous assessment data on the mass of stars in galaxies," Santini said. It will greatly help astronomers study the universe on the largest and longest scale. We find that the systematic uncertainty caused by the hypothetical mass-ray inference model may be as high as several times, which is a far cry from the level of cosmic accuracy we hope to achieve, but based on the James Webb Space Telescope, we will get more accurate star mass data. "

The picture shows the first picture taken by the James Webb Space Telescope. This is the farthest and clearest infrared image ever taken of the universe, which is named "Weber's first Deep Space Photo" and shows the details of galaxy cluster SMACS 0723.

At present, the telescope has proved its optical exploration ability by capturing the clearest and most detailed images of the universe, and has made shocking latest astronomical discoveries that its spectrometer can detect the spectra of distant exoplanets, indicating that it will help scientists describe the atmospheric conditions of exoplanets and determine whether they are really "livable". The latest study suggests that it will also determine the characteristics of the earliest galaxies in the universe, how galaxies evolve, and whether dark matter and dark energy play a key role in the development of the universe.

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