James Webb takes a closer look at the dust disk – Sciencetimes

HE Microscopy, a star very close to the solar system

The closest star to Earth, other than the Sun, is Proxima Centauri. About eight times as far away as the star above (about 32 light years away) is a star called AU Microscopii (AU Microscopii, simply called AU Mic). The star above can be seen in the southern constellation Microscopium.

The star above is located relatively close to Earth, and although it is a variable star whose brightness changes often, it is very difficult to observe with the naked eye from Earth. This is because the star directly above it is a red dwarf, a very dark and cold star. For information, it is predicted that the age of the above star will be approximately 23 million years, and it belongs to a relatively young axis among stars. It is a very young star compared to the total lifetime of a red dwarf.

Microscope ⓒ Stellarium

What is a dust disk?

Eternity must pass in human time, but 20 million years is a very short time when looking at the entire evolution of the stars. When a star reaches its maximum age, the star’s surroundings are very rich in gas and form physically and chemically complex protoplanetary disks, followed by dust disks (or debris disks) where most of the gas has disappear

After a star’s lifetime of about 10 million years, for whatever reason, most of the gas in the disk is gone, which is why the dust disk is very low on average. Therefore, a number of asteroids and planetesimals freely collide with each other, creating a number of small dust particles.

Artist’s view of the dust disk from above © Greg Bacon, John Krist/STScI, ESA, NASA

Small-sized dust is blown away by solar light and stellar winds caused by the sun, and eventually leaves the solar system, which is why the lifetime of the dust above is predicted to be much shorter than that of the parent star in the solar system. . However, observations of dust disks always reveal that they are surrounded by dust, which cannot be explained without constant collisions of asteroids and planets. Thanks to this, the disk above has been nicknamed and named the dust disk.

Imaginary side view of the dust disk © Greg Bacon, John Krist/STScI, ESA, NASA

In the case of our solar system, the Asteroid belt, which is close to Earth and has many asteroids, the Kuiper belt, where many small celestial bodies collect beyond Neptune, and Orr, which is a hypothetical object which has not yet been observed but is known as the birthplace of comets, and the Oort clouds are known as dust disks.

Why are dust disks important?

The dust disks around the stars indicate that most of the planetary formation process has ended. Of course, rocky terrestrial planets are still likely to develop, but dusty disks are a much less complex environment compared to protoplanetary disks, where rocky Earth-like planets orbit at moderate distances from the system’s sun and host temperatures that are friendly to life. it can become a friendly environment for life. At this time, if various miracles occur, such as the introduction of materials essential for the formation of life, such as water or organic matter, through comets or asteroids, life can be born and become an environment where evolution is possible.

Therefore, if life exists in an alien solar system, there is a high probability that a dust disk is formed in that solar system. In other words, if a disk of dust is found around an alien solar system, and if the solar system has a very long life, then there is a chance that life could already exist.

The dusty disk around the star Fomalhaut, also known as the Eye of Sauron © Kalas et al. 2013

Around a fifth of exoplanets are now thought to have disks of dust, but this is likely due to the sensitivity of the telescopes that observe them. Dust disks are mostly made up of dust, but are difficult to observe because their optical depth, which represents the amount of light that is removed by scattering or absorption when passing through the material, is very low.

The dust disk has a very important astronomical meaning because it is a celestial body that contains by-products after most of the formation of the planetary system is complete. Not only does the dust disk contain the history of the formation of the solar system, but many dust disks are actually found orbiting the alien solar system along with several planets.

Because of this, observations of dust disks are currently being studied as an alternative to many planetary observation methods (such as radial velocity, transitive, and positional astronomy). For example, planets in the dust disk leave many small traces by interacting with the disk, and tracking them can compensate for the shortcomings of current planetary observation methods. In particular, planets that are very small or very small and orbit far from the solar system can only be identified by the presence of dust disks.

A dust disk was found around PA microscopy

Since the first dust disk was discovered around the bright star Vega almost 40 years ago in 1984, more than 1,000 dust disks have been discovered so far. Of these, around 170 or more dust discs were spatially resolved, revealing details of the disc’s appearance. In 2004, a disc of dust was discovered under PA microscopy, revealing its appearance.

First observed image of the dust disk around PA microscopy © Kalas et al. 2004

The dust disk around PA microscopy is very distinctive. This is because a PA Microscopy dust disk can only be seen from the side, so it is a good example for observing in detail what the side of the dust disk looks like. FYI, the dust disk of PA Microscopy is not perfectly straight, and the disk seen from the side has a slightly distorted shape.

When viewed from the side, the disc has a slightly distorted shape. © Boccaletti et al. 2015

As with many dust disks and other dust disks in our Solar System, the PA Microscopy dust disk also contains planets. In particular, two planets have so far been predicted to nestle inside the planetary system and the dust disk, but it seems unlikely that these planets orbit the microscopic PA star in the same plane as the dust disk. For this reason, their interaction is predicted to evolve by squeezing the disc seen from the side.

Thus, the AU Microscopy dust disk has been observed not only by space telescopes such as the Hubble Space Telescope, the Spitzer Space Telescope, and the Herschel Space Telescope, but also by several terrestrial telescopes, including the ALMA telescope, a very large radio telescope. . This is because the properties and characteristics of the dust disk can be learned in detail by studying different celestial bodies, such as dust of different sizes, which specialize in observing each wavelength by observing various wavelengths.

James Webb’s Eyes on the AU Microscopy Dust Disc

At this point, a question arises. What would the AU Microscopy dust disk look like as seen by James Webb, the most powerful space telescope in history?

PA Microscopy Dust Disc © NASA, ESA, CSA, Kellen Lawson (NASA-GSFC), Joshua E. Schlieder (NASA-GSFC), Alyssa Pagan (STScI)

The compass arrow for reference shows the direction when looking at the sky, and when looking from below, the direction should be reversed to the standard when looking at the ground. The scale bar is 9.7 astronomical units (AU), which corresponds to 9.7 times the distance from the Earth to the Sun. Through this, it can be seen that the imaged field of view is a huge disk of dust over 100 AU. It is larger than the outer disk of our solar system, the Kuiper Belt. (see high resolution image)

The color-coded filters below show near-infrared and mid-infrared wavelengths converted to visible colors. That is, different filters were used to collect the light, and the color in the name of the filter represents the color of visible light used to represent infrared light passing through that filter.

It’s amazing. Astronomers expected a different dust disk from the mighty James Webb, but never imagined it would be revealed in such detail. The James Webb Space Telescope, showing a much more powerful performance than expected, has shown its skills once again. In particular, PA microscopy dust discs photographed with a near-infrared camera (NIRCam) specialized for near-infrared light at different wavelengths were photographed. (Blue image above: wavelength 3.56 micrometers, red image bottom: wavelength 4.44 micrometers)

PA Microscopy Dust Disc © NASA, ESA, CSA, Kellen Lawson (NASA-GSFC), Joshua E. Schlieder (NASA-GSFC), Alyssa Pagan (STScI)

In near-infrared light, the light from a planet or dust disk is extremely faint compared to the immense light from its parent star. In particular, dust can scatter sunlight mainly in short wavelengths such as near-infrared rays, but even this is very weak compared to sunlight. Additionally, given that the frequency of re-emissions after absorption at the above wavelength is extremely low, it is very difficult to observe dust unless it is far infrared. A technique used in this case is a coronagraph which blocks the light from the parent star.

The size of the coronagraph mask used by the James Webb Space Telescope is different for each observation wavelength, but each mask is large enough to block the starlight of PA Microscopy. Therefore, only the dust disk was photographed with complete obscuration of sunlight. The size of the mask is roughly indicated by the dotted circle in the middle.

The potential of James Webb

First, a large amount of dust was detected around the PA microscopy dust disk. In particular, it can be seen that the size of the disk shown in the picture taken with a shorter wavelength (blue figure) is slightly shorter and brighter. A shorter wavelength scatters smaller particles, so a comparison of the two images can reveal where smaller particles are distributed. The dust above, like other dust disks, is produced by collisions between planets, remnants of planet formation.

Dr said. Kellen Lawson, who led the above study, that he was able to see the above planetary system in more detail because he was able to study parts that are impossible to observe with conventional infrared instruments. Microscopy PA is one of the closest stars to Earth, and the surrounding dust disk is one of the brightest disks visible from Earth. In particular, it has great astronomical significance as it enables detailed observation of the dust disks of young stars.

Interestingly, the image in question was not originally taken to observe the dust disk. The research team predicted that although there was a planet in the dust disk above, it was difficult to observe directly because it was too dark.

Specifically, it began with a plan to search for a gas giant exoplanet orbiting a parent star with an orbit similar to Jupiter and Saturn. This allowed a detailed image of the inner part of the disk, which is distributed closer to the stars than expected, which is an excellent result for constraining many parameters of the dust disk.


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