Dark energy is one of the least satisfying names in astronomy because it sounds more specific than it is. Scientists did not discover a glowing substance called dark energy. They gave that name to the unknown influence associated with the accelerating expansion of the universe. The evidence is strong that the expansion is speeding up […]

The post What Is Dark Energy? The Mystery Behind the Universe’s Accelerating Expansion appeared first on Curiosmos.

Astronomers have combined 2,884 Type Ia supernovae -- which are used to measure cosmic distances -- with cosmic microwave background and galaxy-mapping data, deepening cracks in the standard ‘cosmological constant’ model.

The post Dark Energy May Not Be Constant After All, New Supernova Survey Suggests appeared first on Sci.News: Breaking Science News.

Zooming through the galaxy faster than they should, hypervelocity stars are a curious population of stars whose origins are often difficult to determine. A recent study presents the first evidence of an old, low-mass hypervelocity star launched from the Milky Way’s center, providing clues into this elusive set of fast-moving stars.

Flinging Fast Stars

Astronomers have caught a number of hypervelocity stars zipping through the Milky Way since their first discovery in 2005. With speeds fast enough to escape the galaxy, hypervelocity stars were launched off course by some strong dynamical interaction. One such method, known as the Hills mechanism, predicts that when a binary star system approaches the Milky Way’s central supermassive black hole, one binary member is captured by the black hole and the other is flung away with high velocity.

However, constraining a hypervelocity star’s origin to the galactic center is limited by uncertainties in distances and proper motions, muddling how well researchers have been able to trace their orbits backward. Among a number of candidate galactic center–origin hypervelocity stars, only one has been confidently identified as having been kicked from the galaxy’s center. Intriguingly, this hypervelocity star and most galactic center–origin candidates are young, massive stars — old, low-mass hypervelocity stars from the galactic center have yet to be identified.

What does this dearth of old, low-mass zooming stars mean? Either stars in the galactic center are preferentially young and massive, with fewer than expected old and small stars, or low-mass hypervelocity stars are missed by selection effects, challenging to detect in current surveys. Searching for hypervelocity stars with higher precision and sensitivity may allow astronomers to tease out this missing population and trace back more zooming stars to a Hills mechanism origin.

Discovering An Old Hypervelocity Star

Leveraging high-quality spectra from the Dark Energy Spectroscopic Instrument (DESI) survey and precise astrometry from Gaia, Shunhong Deng (University of Chinese Academy of Sciences; China West Normal University) and collaborators reported the discovery of the hypervelocity star DESI-HVS1. From the spectroscopic and astrometric analyses, the authors determined that DESI-HSV1 is a ~14-billion-year-old low-metallicity star with a mass about 80% that of the Sun’s, moving through the galaxy at 523 km/s.

Exploring the possible origins of this hypervelocity star, the authors integrated the star’s orbit backward in time for one billion years. The backward orbit integrations show the star approaching the galactic center where it then turns around, traveling away faster than the local escape velocity of the galaxy. Even when varying the galactic potential and constants, all orbit integrations suggest DESI-HVS1’s motion through the galaxy is most naturally explained by the Hills mechanism.

While more refined galaxy models and comparison to other candidate galactic center–origin hypervelocity stars are necessary to fully confirm its origins, DESI-HVS1 provides the first compelling evidence for an old, low-mass hypervelocity star candidate consistent with a galactic center launch. This suggests that the observed lack of such stars is likely not a reflection of the Milky Way’s central stellar population, but rather a consequence of observational constraints making such small hypervelocity stars particularly difficult to detect. As large spectroscopic and astrometric surveys continue to advance, the sample of galactic-center hypervelocity star candidates will grow, enabling further exploration of the stellar environment and dynamical processes at the Milky Way’s core.

Citation

“An Old, Low-mass, Metal-poor Hypervelocity Star Candidate Consistent with Galactic Center Origin,” Shunhong Deng et al 2026 ApJL 1003 L9. doi:10.3847/2041-8213/ae6505

The post Shot from the Heart of the Milky Way: Discovery of an Old Hypervelocity Star appeared first on AAS Nova.

The seemingly warped and stretched galaxies in the image above show the work of gravitational lensing, in which the powerful gravitational pull of galaxies or galaxy clusters bends the light from background objects. Xiaosheng Huang (University of San Francisco and Lawrence Berkeley National Laboratory) and coauthors have used a neural network to amass a sample of 3,500 gravitational lensing candidates in data from the Dark Energy Spectroscopic Instrument (DESI) Legacy Surveys. Now, the team has used the Hubble Space Telescope to confirm some of the most promising candidates. Four of the newly confirmed systems are presented in the image above, with the DESI data shown in color and the higher-resolution Hubble data in black and white. Huang and collaborators also demonstrated the ability of their forward-modeling pipeline, GIGA-Lens, to constrain lens properties rapidly, even for large images like those from Hubble. Ultimately, Huang and coauthors hope to identify lensing systems that can be used to search for low-mass dark matter halos and test our theories of cosmology, as well as those that can be monitored for signs of lensed supernovae — providing a way to measure the expansion rate of the universe. To learn more about this sample of gravitational lenses and what the team plans to do next, be sure to check out the full research article linked below.

Citation

“DESI Strong Lens Foundry. I. HST Observations and Modeling with GIGA-Lens,” Xiaosheng Huang et al 2026 ApJ 998 69. doi:10.3847/1538-4357/ae22d2

The post Featured Image: A Treasure Trove of Strong Lenses appeared first on AAS Nova.

After AAS 247 in Phoenix, Arizona, AAS Nova Editor Kerry Hensley and I had the chance to travel about 150 miles south for a tour of Kitt Peak National Observatory.

A Window into Kitt Peak

Located 60 miles southwest of Tucson, Kitt Peak National Observatory (KPNO) resides on a mountain top within the Tohono O’odham Nation reservation. Founded in 1958, Kitt Peak is home to nearly two dozen active telescopes ranging in wavelength coverage and scientific objectives. Ronald Proctor, Lori Allen, and Jacelle Ramon-Sauberan, all serving in crucial roles for the observatory, led our tour around the mountain.

Our visit began in the new Windows on the Universe Center — the first science center inside of a telescope. Situated inside the retired McMath-Pierce Solar Telescope, the Windows Center takes visitors through exhibits exploring the universe, the telescope’s original control room, and the observatory’s connection to the Tohono O’odham Nation.

The center’s lobby introduced visitors to the beautiful land KPNO calls home. Working with Tohono O’odham linguists, Jacelle, the observatory’s Tohono O’odham Nation Education Liaison, curated the lobby exhibit that features the native language and the Nation’s connection to astronomy and the observatory. The science center serves as an educational resource and place of cultural exchange, expanding the relationship between the observatory and the Tohono O’odham Nation. 

After walking through an introduction to the universe exhibit, visitors enter the original control room of the telescope. Mirrors across the room’s ceiling focus the Sun’s light onto table screens where visitors can observe the Sun in real time without burning their eyeballs. In addition to observing the Sun, the solar telescope allowed astronauts in the 1960s to view a projection of the Moon’s surface and plan their landing site for the Apollo 11 mission. Visitors can stand in the same place and witness the instruments that made the moon landing possible.

At the end of the Windows Center is a Science On a Sphere Theater — a spherical display system that allows visitors to see planets, stars, moons, and even large-scale structures of the universe in 3D. Featuring multiple programs, the theater takes visitors through the universe and displays data collected right there on the mountain!

A WIYN for Exoplanetary Science

Though not typically open to the public for tours, our next stop took us to the WIYN 3.5-meter telescope. This telescope is operated and owned by the WIYN Consortium, a partnership between the University of Wisconsin, Indiana University, NSF’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory; formerly NOAO), Pennsylvania State University, and Princeton University. Operating since 1994 with a strong collection of instruments, WIYN has observed galaxies near and far, stars across their lifetimes, and exoplanets tugging on their host stars.

WIYN’s newest instrument, NEID (pronounced “NOO-id”), has been advancing exoplanetary science since its first light in early 2020. Derived from the word meaning “to see” in the Tohono O’odham language, NEID is a high-resolution spectrograph that uses the radial velocity method to detect exoplanets. As a planet orbits its host star, its gravitational pull induces a wobble in the star, and NEID can detect these wobbles with unprecedented precision. This instrument allows astronomers to find exoplanets that were previously undetectable.

The partnership between public and private universities and a government institution was the first of its kind. Through this consortium, hundreds of undergraduate and graduate students have conducted research with WIYN, and the telescope’s suite of instruments have enabled early career astronomers to explore the universe both near and far.

Mysteries of Dark Energy at Mayall

We concluded our tour at the Mayall 4-meter Telescope, the tallest telescope dome on the mountain at a staggering 18 stories high. This iconic telescope saw first light in 1973, and at the time, was the second-largest (in diameter) telescope in the world. Originally built for wide-field optical and infrared studies of the universe, the Mayall has enabled decades of critical scientific research.

Mayall is now home to the Dark Energy Spectroscopic Instrument (DESI), the most powerful multi-object survey spectrograph in the world. The DESI survey measures the impact of dark energy on the expansion of the universe through creating the largest ever 3D map of the universe. Mapping the distances to hundreds of millions of galaxies, DESI has revolutionized cosmology and enabled groundbreaking research into the origins of the universe. 

From the telescope’s massive dome, to the busy DESI control room, to the gallery floor with a nearly 360 degree view of the surrounding desert, the Mayall offers visitors a unique glimpse into Kitt Peak’s history and its future. While WIYN is a hidden gem, the Mayall 4-meter Telescope is open to the public for tours daily, so you can experience the exciting era of research and discovery at KPNO. 

Visit Kitt Peak

Interested in getting a peek yourself? KPNO is open to the public daily with multiple tour types to choose from, including both daytime and nighttime visits! Plan your visit to Kitt Peak here.

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