Careful modelling of the thermal and ionization structure of planetary nebulae, based on observations from the Vainu Bappu Telescope in Kavalur, Tamil Nadu, India, has enabled astronomers to deepen their understanding of the formation and evolution of these unusual hydrogen-deficient stars.

Planetary nebulae are shells of gas and dust ejected by stars like our Sun after they exhaust the hydrogen and helium fuel in their cores—a fate our Sun is expected to face in approximately 5 billion years. As the star’s core contracts due to the lack of nuclear fusion, it heats up and emits intense far-ultraviolet radiation. In the past, these stars appeared planet-like when viewed through small telescopes, a resemblance that led to their name.

While most stars in this late phase of their lives produce core remnants surrounded by tiny residual hydrogen envelopes, about 25% of them exhibit a deficiency of hydrogen and are instead rich in helium on their surfaces. Some of these stars also display strong mass loss and emission lines of ionized helium, carbon, and oxygen, characteristics identified as Wolf-Rayet (WR) features.

IC 2003, a rare planetary nebula, features a hydrogen-deficient central remnant star with WR characteristics.

Although the evolutionary status of typical central stars of planetary nebulae is well-understood, the mechanisms behind the formation of hydrogen-poor stars remain largely unclear. The physical and chemical structures of the nebulae surrounding these stars provide valuable clues about their origin and evolution, making it essential to study their gas and dust in detail.

To investigate this further, astronomers from the Indian Institute of Astrophysics (IIA), an autonomous institute under the Department of Science and Technology, observed IC 2003 using the optical medium-resolution spectrograph (OMR) attached to the 2.3-meter Vainu Bappu Telescope at the Vainu Bappu Observatory in Kavalur, Tamil Nadu. “We also used ultraviolet spectra from the IUE satellite and broadband infrared fluxes from the IRAS satellite archives for this study,” said K. Khushbu, the lead author and Ph.D. student. These combined observations provided critical insights into the role of gas and dust in shaping the thermal structure of the nebula, ultimately enabling the team to derive precise parameters for the central star.

The models they used revealed that the nebula’s parameters, including the ionizing source’s mass and temperature, were significantly different from those predicted by dust-free models. “This study highlights the importance of dust grains in the thermal balance of ionized gas and helps explain the large temperature variations seen in nebulae, which are often key to resolving abundance discrepancies in astrophysical nebulae,” explained Prof. C. Muthumariappan, the supervisor and co-author of the study. “We used a one-dimensional dusty photo-ionization code, CLOUDY17.3, to simulate data from ultraviolet, optical, and infrared observations,” he added.

By modeling the photoelectric heating of the nebula caused by the dust grains, the researchers were able to replicate the thermal structure observed in the planetary nebula. “We even reproduced the large temperature gradient typically seen in nebulae with WR stars. Our determination of element abundances, such as helium, nitrogen, and oxygen, differs significantly from the values obtained empirically,” Khushbu noted.

The study also provided accurate grain size distributions within the nebula and highlighted the crucial role of photoelectric heating in explaining temperature variations. From their models, the researchers derived accurate values for the luminosity, temperature, and mass of the central star. They concluded that the star’s initial mass was 3.26 times that of the Sun, indicating it was a more massive star.

This research advances our understanding of the complex processes at work in the evolution of hydrogen-deficient stars and offers valuable insights into the origins of the unique features observed in planetary nebulae.

Asteroids that could potentially impact Earth vary greatly in size, from the catastrophic 10-kilometer-wide asteroid that caused the extinction of the dinosaurs to much smaller ones that strike far more frequently. Now, an international team of researchers, led by physicists at MIT, has discovered a new way to spot the smallest asteroids in our solar system’s main asteroid belt, which could provide critical insights into the origins of meteorites and planetary defense.

The team’s breakthrough approach allows astronomers to detect decameter asteroids—those just 10 meters across—much smaller than those previously detectable, which were about one kilometer in diameter. This marks the first time such small asteroids in the asteroid belt have been spotted, potentially leading to better tracking of near-Earth objects that could pose a threat.

“We have been able to detect near-Earth objects down to 10 meters in size when they are really close to Earth,” said lead author Artem Burdanov, a research scientist at MIT’s Department of Earth, Atmospheric and Planetary Sciences. “We now have a way of spotting these small asteroids when they are much farther away, so we can do more precise orbital tracking, which is key for planetary defense.”

The team used their innovative method to detect over 100 new decameter asteroids, ranging from the size of a bus to several stadiums wide. These are the smallest asteroids ever found in the main asteroid belt, located between Mars and Jupiter, where millions of asteroids orbit.

The findings, published today in Nature, have the potential to improve asteroid tracking efforts, which are critical for understanding the risk of future impacts. Scientists hope that the method could be applied to identify asteroids that may one day approach Earth.

The research team, which includes MIT planetary science professors Julien de Wit and Richard Binzel, as well as collaborators from the University of Liege, Charles University, and the European Space Agency, among others, utilized the James Webb Space Telescope (JWST) for their discovery. JWST’s sensitivity to infrared light made it an ideal tool for detecting the faint infrared emissions of asteroids, which are far brighter at these wavelengths than in visible light.

The team’s approach also relied on an imaging technique called “shift and stack,” which involves aligning multiple images of the same field of view to highlight faint objects like asteroids. This technique was originally developed for exoplanet research but was adapted for asteroid detection.

The researchers believe that these new findings will help improve our understanding of asteroid population

By processing over 10,000 images of the TRAPPIST-1 system—collected to study the planets in that distant star system—the researchers identified eight known asteroids and an additional 138 new ones. These newly discovered asteroids are the smallest main belt asteroids ever detected, with diameters as small as 10 meters.

“This is a totally new, unexplored space we are entering, thanks to modern technologies,” Burdanov said. “It’s a good example of what we can do as a field when we look at the data differently. Sometimes there’s a big payoff, and this is one of them.”

The researchers believe that these new findings will help improve our understanding of asteroid populations, including the many small objects that result from collisions among larger asteroids. Miroslav Broz, a co-author from Charles University in Prague, emphasized the importance of studying these decameter asteroids to model the creation of asteroid families formed from larger, kilometer-sized collisions.

De Wit, a co-author, highlighted the significance of the discovery: “We thought we would just detect a few new objects, but we detected so many more than expected, especially small ones. It is a sign that we are probing a new population regime, where many more small objects are formed through cascades of collisions.”

(With inputs from MIT)

US space agency NASA’s Imaging X-ray Polarimetry Explorer (IXPE) has provided new insights into the structures around a stellar-mass black hole, enhancing our understanding of the swirling disk of material and the shifting plasma region known as the corona. The black hole is part of the binary system Swift J1727.8-1613, and was discovered during an extraordinary brightening event in the summer of 2023. This outburst briefly made the black hole outshine nearly all other X-ray sources, according to NASA.

Swift J1727 is the first such black hole to be observed by IXPE as it went through the stages of an X-ray outburst, from its onset to its peak and eventual return to inactivity. Scientists say the data collected during this outburst offers first-time insight into the behaviour and evolution of black hole X-ray binary systems.

Astrophysicist Alexandra Veledina, from the University of Turku in Finland, described the event as “incredibly quick.” From the initial detection of the outburst, Swift J1727 took only days to reach its peak. By that time, IXPE and other telescopes were already gathering crucial data to track the outburst’s progression. “It was exhilarating to observe the outburst all the way through its return to inactivity,” Veledina added.

The outburst, which briefly surpassed the brightness of the Crab Nebula (the standard X-ray reference), lasted until late 2023. Notably, this event occurred just 8,800 light-years away from Earth, making it an exceptional discovery in terms of both brightness and proximity. The system was named after the Swift Gamma-ray Burst Mission, which initially detected the event on August 24, 2023, using its Burst Alert Telescope.

The findings, published in The Astrophysical Journal and Astronomy & Astrophysics, gives a deeper understanding of the dynamics of black hole systems and the role of X-ray binaries in the broader cosmic landscape.