NASA Webb Finds Early-Universe Analog’s Unexpected Talent for Making Dust - UNIVERSE

Using NASA’s James Webb Space Telescope, astronomers have spotted two rare kinds of dust in the dwarf galaxy Sextans A, one of the most chemically primitive galaxies near the Milky Way. The finding of metallic iron dust and silicon carbide (SiC) produced by aging stars, along with tiny clumps of carbon-based molecules, shows that even when the universe had only a fraction of today’s heavy elements, stars and the interstellar medium could still forge solid dust grains. This research with Webb is reshaping ideas about how early galaxies evolved and developed the building blocks for planets, as NASA explores the secrets of the universe and our place in it.

Sextans A lies about 4 million light-years away and contains only 3 to 7 percent of the Sun’s metal content, or metallicity, the astrophysical term for elements heavier than hydrogen and helium. Because the galaxy is so small, unlike other nearby galaxies, its gravitational pull is too weak to retain the heavy elements like iron and oxygen created by supernovae and aging stars.

Galaxies like it resemble those that filled the early universe just after the big bang, when the universe was made of mostly hydrogen and helium, before stars had time to enrich space with ‘metals.’ Because it is relatively close, Sextans A gives astronomers a rare chance to study individual stars and interstellar clouds under conditions similar to those shortly after the big bang.

“Sextans A is giving us a blueprint for the first dusty galaxies,” said Elizabeth Tarantino, postdoctoral researcher at the Space Telescope Science Institute and lead author of the results in one of the two studies presented at a press conference at the 247th meeting of the American Astronomical Society in Phoenix. “These results help us interpret the most distant galaxies imaged by Webb and understand what the universe was building with its earliest ingredients.”

Image A: Sextans A PAHs Pull-out (NIRCam and MIRI Image)

Images from NASA’s James Webb Space Telescope of the dwarf galaxy Sextans A reveal polycyclic aromatic hydrocarbons (PAHs), large carbon-based molecules that can be a signifier of star formation. The inset at the top right zooms in on those PAHs, which are represented in green.

Image: NASA, ESA, CSA, Elizabeth Tarantino (STScI), Martha Boyer (STScI), Julia Roman-Duval (STScI); Image Processing: Alyssa Pagan (STScI)

Forging dust without usual ingredients

One of those studies, published in the Astrophysical Journal, honed in on a half a dozen stars with the low-resolution spectrometer aboard Webb’s MIRI (Mid-Infrared Instrument). The data collected shows the chemical fingerprints of the bloated stars very late in their evolution, called asymptotic giant branch (AGB) stars. Stars with masses between one and eight times that of the Sun pass through this phase.

“One of these stars is on the high-mass end of the AGB range, and stars like this usually produce silicate dust. However, at such low metallicity, we expect these stars to be nearly dust-free,” said Martha Boyer, associate astronomer at the Space Telescope Science Institute and lead author in that second companion study. “Instead, Webb revealed a star forging dust grains made almost entirely of iron. This is something we’ve never seen in stars that are analogs of stars in the early universe.”

Silicates, the usual dust formed by oxygen-rich stars, require elements like silicon and magnesium that are almost nonexistent in Sextans A. It would be like trying to bake cookies in a kitchen without flour, sugar, and butter. 

A normal cosmic kitchen, like the Milky Way, has those crucial ingredients in the form of silicon, carbon, and iron. In a primitive kitchen, like Sextans A, where almost all of those ingredients are missing, you barely have any proverbial flour or sugar. Therefore, astronomers expected that without those key ingredients, stars in Sextans A couldn’t “bake” much dust at all. 

However, not only did they find dust, but Webb showed that one of these stars used an entirely different recipe than usual to make that dust. 

The iron-only dust, as well as silicon carbide produced by the less massive AGB stars despite the galaxy’s low silicon abundance, proves that evolved stars can still build solid material even when the typical ingredients are missing. 

“Dust in the early universe may have looked very different from the silicate grains we see today,” Boyer said. “These iron grains absorb light efficiently but leave no sharp spectral fingerprints and can contribute to the large dust reservoirs seen in far-away galaxies detected by Webb.”

Image B: Sextans A Context Image (Webb and KPNO)

NASA’s James Webb Space Telescope’s image of a portion of the nearby Sextans A galaxy is put into context using a ground-based image from the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory.

Image: STScI, NASA, ESA, CSA, KPNO, NSF's NOIRLab, AURA, Elizabeth Tarantino (STScI), Phil Massey (Lowell Obs.), George Jacoby (NSF, AURA), Chris Smith (NSF, AURA); Image Processing: Alyssa Pagan (STScI), Travis Rector (UAA), Mahdi Zamani (NSF's NOIRLab), Davide De Martin (NSF's NOIRLab)

Tiny clumps of organic molecules

In the companion study, currently under peer review, Webb imaged Sextans A’s interstellar medium and discovered polycyclic aromatic hydrocarbons (PAHs), which are complex, carbon-based molecules and the smallest dust grains that glow in infrared light. The discovery means Sextans A is now the lowest-metallicity galaxy ever found to contain PAHs.

But, unlike the broad, sweeping PAH emission seen in metal-rich galaxies, Webb revealed PAHs in tiny, dense pockets only a few light-years across.

“Webb shows that PAHs can form and survive even in the most metal-starved galaxies, but only in small, protected islands of dense gas,” said Tarantino. 

The clumps likely represent regions where dust shielding and gas density reach just high enough to allow PAHs to form and grow, solving a decades-long mystery about why PAHs seem to vanish in metal-poor galaxies.

The team has an approved Webb Cycle 4 program to use high-resolution spectroscopy to study the detailed chemistry of Sextans A’s PAH clumps further. 

Image C: Giant Star in Dwarf Galaxy Sextans A (Spectrum)

This graph shows a spectrum of an Asymptotic Giant Branch (AGB) star in the Sextans A galaxy. It compares data collected by NASA’s James Webb Space Telescope with models of mostly silicate-free dust and dust containing at least 5% silicates. 

Illustration: NASA, ESA, CSA, STScI, Joseph Olmsted (STScI)

Connecting two discoveries

Together, the results show that the early universe had more diverse dust production pathways than the more established and proven methods, like supernova explosions. Additionally, researchers now know there’s more dust than predicted at extremely low metallicities. 

“Every discovery in Sextans A reminds us that the early universe was more inventive than we imagined,” said Boyer. “Clearly stars found a way to make the building blocks of planets long before galaxies like our own existed.”

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

To learn more about Webb, visit: https://science.nasa.gov/webb  

Source: NASA Webb Finds Early-Universe Analog's Unexpected Talent for Making Dust - NASA Science   

Searching for light dark matter by tracking its direction with quantum sensors - Astronomy & Space Astronomy - UNIVERSE

Credit: Scott Lord from Pexels

Dark matter is an elusive type of matter that does not emit, absorb or reflect light, interacting very weakly with ordinary matter. These characteristics make it impossible to detect using conventional technologies used by physicists to study matter particles.

As it has never been observed before, the exact composition of dark matter remains unknown. One proposed theory is that this elusive type of matter is comprised of light particles with very small masses, below 1 eV (electronvolt), which behave more like waves than particles.

Researchers at the University of Tokyo and Chuo University recently explored the possibility of searching for sub-GeV dark matter using quantum sensors, advanced systems that rely on quantum mechanical effects to detect extremely weak signals.

Their paper, published in Physical Review Letters, highlights the potential of these highly sensitive sensing systems for tracking the velocity and direction of light dark matter.

"I was checking recent papers in the quantum physics category on arXiv and found that distributed quantum sensing has become a fairly hot topic," Hajime Fukuda, first author of the paper, told Phys.org.

"We were then wondering if we can use this technology in our field (i.e., high-energy physics) and came up with the idea to use it for dark matter detection."

Measuring the velocity and direction of dark matter

The recent study by Fukuda and his colleagues was aimed at combining recent quantum engineering advances with particle physics, specifically to improve ongoing searches for dark matter. To search for hypothetical heavy dark matter particles, physicists have so far primarily tried to pick up small vibrations or signals that would emerge if these particles collided with specific materials, atoms or nuclei inside dark matter detectors.

"When employing these approaches, it is straightforward to measure the velocity of dark matter, although experimentally this is of course difficult," said Fukuda.

"For light dark matter, however, we typically use excitation of some discrete mode, so that it is not possible to see the velocity. We found that we can measure the velocity of light dark matter not by measuring spatially extended signals (recoil tracks) but by measuring by spatially extended detectors."

In their paper, the researchers thus introduced an entirely new strategy that could be used to measure the velocity of dark matter and the direction it is coming from. This strategy entails the use of several dark matter detectors and a quantum measurement protocol.

The data collected by these detectors would be treated as quantum sensor data, from which researchers could extract information about the velocity and direction of dark matter. Fukuda and their colleagues performed a series of analyses to assess the potential of their approach and found that it would significantly improve the sensitivity of detectors.

"Earlier works introduced other methods to search for light dark matter, which for instance relied on an elongated detector or a classical array of detectors," explained Fukuda. "However, these methods depend on the detailed type of the interaction, while our method relies on a quantum sensor array and is far more general. Also, the sensitivity attained by our method is better."

A new route for future dark matter searches

The new approach to search for light dark matter introduced by this research team could soon be refined further and applied in real experiments. This recent study could also inspire other particle and high-energy physicists to explore the potential of quantum sensing systems for both dark matter searches and the precise study of other particles.

"We showed that quantum methods could play an important role in high-energy physics," added Fukuda.

"I think that there could be other applications for quantum sensors in our field and am excited to continue exploring this possibility. In our next studies, we could also improve our method and try to measure not only the velocity but also the dark matter distribution by the sensor array." 

by Ingrid Fadelli, Phys.org

edited by Sadie Harley, reviewed by Robert Egan 

Source: Searching for light dark matter by tracking its direction with quantum sensors