NASA’s James Webb Space Telescope has captured highly detailed images showing the complex layers of interstellar dust and gas. These observations, collected through light echoes from a supernova explosion, “are allowing astronomers to map the true 3D structure of this interstellar dust and gas (known as the interstellar medium) for the first time,” stated NASA in a release.

The light echoes, originating from a star’s collapse over 350 years ago, have travelled across vast distances to illuminate surrounding gas and dust. The explosion caused intense X-rays and ultraviolet light, which reached interstellar material, causing it to glow in the infrared. These cosmic remnants are now visible in stunning detail due to Webb’s advanced infrared technology.

“We were pretty shocked to see this level of detail,” said Jacob Jencson, principal investigator from Caltech.

The images reveal layers of interstellar material, some resembling the structure of an “onion”. Josh Peek of the Space Telescope Science Institute in Baltimore, said, “We see layers like an onion. We think every dense, dusty region that we see, and most of the ones we don’t see, look like this on the inside. We just have never been able to look inside them before.”

The Webb images show dense sheets of gas and dust stretching across hundreds of astronomical units. These sheet-like structures were not previously observed, challenging previous understanding of the interstellar medium.

“We did not know that the interstellar medium had structures on that small of a scale, let alone that it was sheet-like,” Peek said.

In addition to the sheet-like structures, Webb’s images reveal intricate magnetic features, suggesting interstellar magnetic fields influence these formations. Some areas appear as magnetic “islands” within the more uniform fields that dominate the interstellar medium, stated NASA.

The light echoes were first detected by NASA’s retired Spitzer Space Telescope, but Webb’s high-resolution imaging has provided clearer views of these cosmic phenomena. The echoes result from a supernova explosion, where light interacts with clumps of gas and dust, heating and illuminating them in an expanding pattern.

Armin Rest from the Space Telescope Science Institute likened the 3D mapping of the interstellar material to “the astronomical equivalent of a medical CT scan.”

“We have three slices taken at three different times, which will allow us to study the true 3D structure. It will completely change the way we study the interstellar medium,” Rest said.

Webb’s future observations will include spectroscopic observations of the light echoes using its Mid-Infrared Instrument (MIRI). This will allow scientists to study changes in the composition of the dust before, during, and after it is illuminated by the light echoes.

The discovery of these intricate details is a major milestone in space exploration. NASA Administrator Bill Nelson reflected on the mission’s success, saying, “Every image, every discovery, shows a portrait not only of the majesty of the universe but the power of the NASA team and the promise of international partnerships.”

Spiral galaxy NGC 628, located 32 million light-years away from Earth, is seen in an undated image from the James Webb Space Telescope.
| Photo Credit: Reuters

Fresh corroboration of the perplexing observation that the universe is expanding more rapidly than expected has scientists pondering the cause – perhaps some unknown factor involving the mysterious cosmic components dark energy and dark matter.

Two years of data from NASA’s James Webb Space Telescope have now validated the Hubble Space Telescope’s earlier finding that the rate of the universe’s expansion is faster – by about 8% – than would be expected based on what astrophysicists know of the initial conditions in the cosmos and its evolution over billions of years. The discrepancy is called the Hubble Tension.

The observations by Webb, the most capable space telescope ever deployed, appear to rule out the notion that the data from its forerunner Hubble was somehow flawed due to instrument error.

“This is the largest sample of Webb Telescope data – its first two years in space – and it confirms the puzzling finding from the Hubble Space Telescope that we have been wrestling with for a decade – the universe is now expanding faster than our best theories can explain,” said astrophysicist Adam Riess of Johns Hopkins University in Maryland, lead author of the study published on Monday (December 9, 2024) in the Astrophysical Journal.

“Yes, it appears there is something missing in our understanding of the universe,” added Riess, a 2011 Nobel laureate in physics for the co-discovery of the universe’s accelerating expansion. “Our understanding of the universe contains a lot of ignorance about two elements – dark matter and dark energy – and these make up 96% of the universe, so this is no small matter.”

“The Webb results can be interpreted to suggest there may be a need to revise our model of the universe, although it is very difficult to pinpoint what this is at the moment,” said Siyang Li, a Johns Hopkins doctoral student in astronomy and astrophysics and a study co-author.

Dark matter, thought to comprise about 27% of the universe, is a hypothesised form of matter that is invisible but is inferred to exist based on its gravitational effects on ordinary matter – stars, planets, moons, all the stuff on Earth – which accounts for roughly 5% of the universe.

Dark energy, believed to comprise approximately 69% of the universe, is a hypothesised form of energy permeating vast swathes of space that counteracts gravity and drives the universe’s accelerating expansion.

What might explain the anomalous expansion rate?

“There are many hypotheses that involve dark matter, dark energy, dark radiation – for example, neutrinos (a type of ghostly subatomic particle) – or gravity itself having some exotic properties as possible explanations,” Riess said.

The researchers employed three different methods to measure a specific telltale metric – distances from Earth to galaxies where a type of pulsating star called Cepheids have been documented. The Webb and Hubble measurements were in harmony.

The universe’s expansion rate, a figure called the Hubble constant, is measured in kilometers per second per megaparsec, a distance equal to 3.26 million light-years. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

Under the standard model of cosmology – basically, the conventional wisdom concerning the universe – the value of the Hubble constant should be about 67-68. The Hubble and Webb data give a value averaging about 73, with a range of about 70-76.

The Big Bang event 13-14 billion years ago initiated the universe, and it has been expanding ever since. Scientists in 1998 disclosed that this expansion was actually accelerating, with dark energy as the hypothesized reason.

The new study looked at Webb data covering about a third of Hubble’s full slate of relevant galaxies. The researchers in 2023 announced that earlier interim Webb data validated the Hubble findings.

So how might this Hubble Tension mystery be solved?

“We need more data to better characterize this clue. Exactly what size is it (the discrepancy)? Is the mismatch at the lower end – 4-5% – or the higher end – 10-12% – of what the current data allows? Over what range of cosmic time is it present? These will further inform ideas,” Riess said.

An artist’s illustration shows the nearest brown dwarf to Earth. ESO-I. Crossfield-N.
| Photo Credit: Reuters

The weather report is in for the two brown dwarfs – celestial bodies bigger than a planet but smaller than a star – closest to us. It is inclement, to put it mildly: blazingly hot, with a toxic chemical cocktail swirling in the atmosphere and clouds of silicate particles blowing around like a Saharan dust storm.

Researchers have used James Webb Space Telescope observations to conduct detailed examinations of the atmospheric conditions on brown dwarfs, specifically a pair that orbit each other around six light years from Earth, quite close by cosmic standards. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

The Webb data provided a three-dimensional look at how the weather changed over the course of a brown dwarf’s rotation – the larger of the two taking seven hours and the smaller five hours – with multiple layers of clouds found at different atmospheric depths.

Both have atmospheres dominated by hydrogen and helium, with trace amounts of water vapor, methane and carbon monoxide. The temperature at their cloud tops was about 1,700 degrees Fahrenheit (925 degrees Celsius), similar to a candle flame.

“In this study, we created the most detailed ‘weather maps’ for any brown dwarf to date,” said astronomer Beth Biller of the University of Edinburgh’s Institute for Astronomy, lead author of the study published on Monday in the scientific journal Monthly Notices of the Royal Astronomical Society.

Brown dwarfs are neither a star nor a planet, but something in between. They give off their own light thanks to their sheer heat – “just like you would see embers in a fire glowing red because of how hot they are,” Biller said. It was that light that the researchers observed with Webb. Unlike stars, brown dwarfs do not have nuclear fusion occurring at their core.

“Like planets, but unlike stars, brown dwarfs can also have clouds made out of precipitates in their atmospheres. However, while we have water clouds on Earth, the clouds on brown dwarfs are much hotter and likely made up of hot silicate particles -kind of like a very hot Saharan dust storm,” Biller said.

The current scientific thinking is that brown dwarfs form from large clouds of gas and dust like stars do, but fall short of mass sufficient to ignite nuclear fusion. Their composition is similar to gas giant planets like Jupiter, our solar system’s largest planet. Their mass is up to 80 times greater than Jupiter’s. By comparison, the sun’s mass is about 1,000 times greater than Jupiter’s.

The two brown dwarfs examined by Webb formed about 500 million years ago. Each has a diameter comparable to Jupiter’s. One is 35 times more massive than Jupiter, and the other 30 times.

Webb discerned how their light varied as different atmospheric features rotated in and out of view.

“The fast rotation of both objects helps to drive their weather patterns, and if you could actually directly see the cloud-top structure, you probably would be able to see bands and vortices, like the Great Red Spot, as you do on Jupiter,” Biller said.

“In the future, similar techniques could be used to study weather on potentially habitable exoplanets,” Biller added, referring to planets beyond our solar system.

Brown dwarfs are relatively common. About 1,000 are known, compared to more than 5,000 known exoplanets.

Webb examines the cosmos mainly in the infrared, while its Hubble Space Telescope predecessor does so primarily at optical and ultraviolet wavelengths.

“The atmospheres of brown dwarfs are highly complex. Webb provides a huge leap forward in our ability to understand these atmospheres by providing unprecedented wavelength range and sensitivity,” said astronomer and study co-author Johanna Vos of Trinity College Dublin in Ireland.

“These different wavelengths allow us to monitor the atmosphere from very deep to very shallow, giving a comprehensive look at the full extent of the atmosphere,” Vos added.