NASA’s Chandra Examines Milky Way at Arms’ Length - UNIVERSE

This sequence begins with an artist’s concept showing the Milky Way galaxy as seen from above, with the estimated positions of spiral arms based on previous data. Next is an updated artist’s concept of the Milky Way, where the positions of the two spiral arms most distant from the center of the galaxy have been adjusted based on newly processed X-ray data from NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton. Both arms may be more distant than previously thought.

NASA/CXC/A. Hobart

A new result using NASA’s Chandra X-ray Observatory shows that the outer spiral arms in the Milky Way galaxy may reach wider than previously thought. This finding may lead astronomers to adjust their understanding of our home galaxy’s structure.

A team of astronomers made this discovery by making precise measurements of distances to dust clouds in the Milky Way’s spiral arms using data from both NASA’s Chandra and XMM-Newton, an ESA (European Space Agency) mission with NASA contributions. The results are described in a new paper published Wednesday in the Astronomy & Astrophysics journal.

The researchers determined the distances by studying rings around gamma-ray bursts, some of the brightest bursts of light in the universe, which arise from the collapse of massive stars or the merger of neutron stars. They are located at enormous distances, well beyond the confines of our galaxy.

An artist’s concept showing the Milky Way galaxy as seen from above, with the estimated positions of spiral arms based on previous data, in blue. Overlaid on this is an updated view of the Milky Way showing different positions for the two outermost spiral arms, shown in red and bordered by dashed lines. Both arms may be more distant than previously thought, based on newly processed X-ray data from Chandra and XMM.

NASA/CXC/SAO/M.Weiss

This distance measurement technique capitalized on the phenomenon of light echoes, where the light from the gamma-ray burst bounced off dust clouds in the spiral arms. The diameters of the rings in X-rays give the distances to Earth, with larger rings being generated by dust clouds closer to us.

“This is a very direct way – relying only on geometry – to precisely measure distances to the Milky Way’s spiral arms,” said Beatrice Vaia, who led the study while a PhD student in a joint program between Scuola Universitaria Superiore IUSS Pavia and University of Trento in Italy. “Most other methods rely on assumptions about how the Milky Way rotates, which become increasingly uncertain in the outer regions of our galaxy."

Despite a century of awareness of the Milky Way’s spiral arms, astronomers are still working toward precise characterization of its arms because of Earth’s position within one. Dust and gas also block the view to other arms.

The researchers used three different gamma-ray bursts to determine the distances to three spiral arms in the Milky Way. In order of increasing distances from the Galactic Center, they are the Perseus, the Outer, and the Outer Scutum-Centaurus arms. Along the direction of one of the bursts, they found that both the Outer and Outer Scutum-Centaurus arms are about 10% more distant than astronomers previously thought.

“The differences are small, but any revision of these distances is important because they are so fundamental for understanding our galaxy,” said co-author Ilaria Fornasiero, who was a PhD student in the same program as the leading author. “For example, this could mean that astronomers have to revise estimates of the mass of the galaxy, because that affects how wide the arms stretch.”

The images include X-ray data from Chandra and optical data from Pan-STARRS. The composite image shows X-ray rings generated by a gamma-ray burst (GRB), a bright X-ray source located outside our galaxy. In a phenomenon called light echoes, the X-rays from the GRB bounced off dust clouds in the spiral arms of our galaxy. The diameters of the rings in the Chandra data give the distances of the dust clouds to Earth, with larger rings being generated by dust clouds closer to us. The GRB is located at the center of the circles defining the rings, to the left of the X-ray data outlined by the white square.

X-ray: NASA/CXC/INAF/B. Vaia et al.; Optical: Pan-STARRS; Image processing: NASA/CXC/SAO/N.Wolk & P.Edmonds

The team also used their data to estimate that the dust cloud in the most distant arm is about 3,500 light-years wide. These findings show that their measurements apply to the full thickness of the spiral arm, rather than a random, isolated dust cloud that may not fully be representative of the arm’s location.

While this technique provided major improvements in accuracy according to the researchers, it may be difficult to use it for further measurements because bright gamma-ray bursts that are visible through the plane of the galaxy are rare.

“We’re relying on the universe to provide us with these events, and so far, over 25 years, we’ve only found a handful that we can use,” said co-author Andrea Tiengo of Scuola Universitaria Superiore IUSS Pavia. “That said, we will continue to be on the lookout for more.”

NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.

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To learn more about Chandra, visit: https://nasa.gov/chandra

To learn more about NASA’s Chandra mission, visit: https://nasa.gov/chandra 

Source: NASA’s Chandra Examines Milky Way at Arms’ Length - NASA Science 

Why Does Time Feel Faster With Age?

Ask most adults in their forties or fifties and they will tell you the same thing: the years are moving faster than they used to. A decade that once felt endless now seems to compress into a handful of summers. This is not nostalgia or complaint. It is a consistent, cross-cultural phenomenon that people report with enough regularity that researchers have been trying to explain it for decades. A study published in September 2025 may have found its clearest neural explanation yet.

The Hitchcock experiment

The study, by Lugtmeijer and colleagues at the University of Cambridge, drew on data from the Cambridge Centre for Ageing and Neuroscience project, a long-running effort to track how the brain changes across the adult lifespan. The team recruited 557 people aged 18 to 88 and scanned their brains while they watched a segment of an old Alfred Hitchcock television program.

The choice of stimulus was deliberate. Hitchcock’s direction is rich in moment-to-moment shifts: changes in tension, attention, camera angle, and emotional register. The researchers used a technique called neural state segmentation to identify how the brain divided this continuous stream of experience into discrete chunks, what they called neural “events.” Each time the brain registered a meaningful shift in what was happening, it created a new event boundary. The more boundaries, the more the brain had carved the experience into distinct, memorable episodes.

Older brains carve fewer chapters

What the scans showed was striking. Older participants produced significantly fewer and longer neural events while watching the same material. Their brains were parsing the same stretch of time into fewer distinct segments, particularly in the visual cortex and in a prefrontal region associated with episodic memory encoding. The “chapters” were longer and blurrier.

The researchers tied this to a well-documented process called neural dedifferentiation, in which brain regions become gradually less specialized with age. A younger visual cortex responds sharply to shifts in visual content. An older one tends to respond more broadly, with less precision. Fewer sharp responses mean fewer event boundaries, which means fewer distinct memories laid down per unit of clock time.

“When we look back on a period of time, we are essentially counting the memories we have from it. If fewer distinct events were encoded, the period feels shorter in retrospect, even if the clock said otherwise.”

Why childhood summers felt so long

This finding offers a neural account of something people have been noticing informally for as long as there has been human reflection on time. Childhood is full of new experiences, unfamiliar environments, first encounters with things not yet understood. A young brain encountering novelty creates sharp, numerous event boundaries. Every day contains many distinct memories. Looking back, the period feels long, almost endless.

Adult life, particularly for people settled into routine, contains far fewer genuinely novel experiences. A familiar commute, a meeting very like last week’s meeting, a dinner much like last Tuesday’s dinner: these events produce fewer new boundaries, fewer distinct memories, and in retrospect feel like they passed in a blur.

The neurological and the experiential accounts are consistent with each other. The 2025 study adds a mechanism to a phenomenon that previously had only anecdote.

Can anything slow the clock?

The research group was careful not to overstate the implications, but the logic of their findings does point in a practical direction. If time feels faster when the brain encodes fewer distinct events, then anything that increases novelty and attention should, in principle, make time feel more expansive. Travel, new skills, unfamiliar social environments, and any experience that forces genuine attention rather than automatic processing all create more event boundaries. The effect is stronger during the experience than after it: a slow, boring afternoon feels long in the moment but short in memory. A rich, novel day feels fast in the moment but long in memory.

The broader implication is that time perception is not a passive recording but an active construction. The brain does not register every second equally. It creates a narrative from events, and the richness of that narrative, more than the number of seconds it spans, is what determines how long a period of life seems to have been.

A question of attention

Neural dedifferentiation is real and it does increase with age, but it is not entirely fixed. Cognitive engagement, physical exercise, and continued learning have all been associated with slower rates of dedifferentiation. Whether any of these interventions measurably changes time perception is not yet known. What the Lugtmeijer study establishes is where to look: at the sharpness of neural event boundaries, and at the question of how many distinct moments a brain can be persuaded to notice in the course of a day.

Sources

·         Lugtmeijer, S., et al. (2025). Age-related differences in neural event segmentation and temporal memory. Communications Biology. Cambridge Centre for Ageing and Neuroscience (Cam-CAN).

·         Zacks, J.M., et al. (2007). Event perception: A mind-brain perspective. Psychological Bulletin.

·         Haber, S., et al. (2023). Neural dedifferentiation and cognitive aging. Neuroscience & Biobehavioral Reviews.

Source: Why Does Time Feel Faster With Age? – Scents of Science