OrbitalHub

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SS 433 is one of the most extraordinary and enigmatic objects in the Milky Way, a system whose extreme physics has made it a cornerstone of high-energy astrophysics for more than four decades. Located about 5,500 light-years away in the direction of the constellation Aquila, SS 433 is the first known microquasar—a stellar binary with powerful relativistic jets resembling those of supermassive black holes, but scaled to the mass of a single star. At the heart of the system is a compact object whose nature continues to generate debate: although a neutron star cannot be definitively ruled out, mounting evidence points toward SS 433 harboring a stellar-mass black hole, one that is actively feeding on material from its companion star and launching jets at speeds approaching one-quarter the speed of light. The extreme conditions in this system make SS 433 a natural laboratory for studying accretion physics, jet formation, and the limits of matter under relativistic stresses.

One of the defining features of SS 433 is its precessing jet system, a dynamic structure that distinguishes it from nearly all other known X-ray binaries. As the compact object accretes material from its massive donor star—likely an A-type supergiant—the inflowing gas forms a dense, hot accretion disk. From the inner regions of this disk, two opposing jets are launched at roughly 0.26c, a velocity that directly reveals the presence of an intense gravitational well. The jets do not simply stream outward in a straight line; instead, the axis of the disk—and therefore the jets—precesses like a spinning top, tracing a conical pattern every 162 days. As the jets sweep across the sky, their emission undergoes extreme Doppler shifting, which astronomers detect as visibly changing redshifts and blueshifts in the spectral lines of hydrogen and heavier elements. This unique behavior is what enabled SS 433 to become the first system in which relativistic jet speeds were measured outside of an active galactic nucleus.

The environment surrounding SS 433 adds yet another layer of complexity. The system lies at the center of the radio nebula W50, a distorted supernova remnant whose elongated, “manatee-shaped” structure appears to have been sculpted over tens of thousands of years by the persistent, high-energy jets emerging from SS 433. The interaction between these jets and the expanding supernova remnant creates shock waves, particle acceleration sites, and X-ray bright knots that provide insight into how jets deposit energy into their surroundings. Observations from XMM-Newton, Chandra, and radio observatories have revealed that the jets remain collimated over astonishing distances—on the order of dozens of light-years—before finally dispersing into the ambient medium. This durability indicates a stable launching mechanism and considerable energy output, both of which bolster the argument for a black hole rather than a neutron star as the jet-driving engine.

The debate over the compact object’s identity centers on mass estimates derived from orbital dynamics, emission modeling, and binary evolution theory. Early measurements suggested a mass around 10 M☉, comfortably within black hole territory, though later studies have proposed somewhat lower values consistent with heavy neutron stars. Yet the prevailing interpretation emphasizes the system’s extraordinary luminosity, steady high-rate accretion, and jet power—properties more naturally explained by a black hole feeding at or above its Eddington limit. SS 433 is one of the very few objects in the Galaxy that appears to host a supercritical accretion disk, a configuration in which the infalling matter produces thick disk winds and intense radiation pressure, conditions difficult for neutron stars to sustain. Simulations indicate that such a disk geometry can produce the observed precession and collimated outflows, providing a cohesive theoretical framework that aligns with decades of observation.

In the broader astrophysical context, SS 433 continues to serve as a bridge between stellar-mass black holes in our galaxy and the majestic quasars found in distant galaxies. Although microscopic by comparison, its disk–jet dynamics follow the same physical rules that govern the supermassive black holes in active galactic nuclei. Because SS 433 is nearby, bright, and persistently active, it offers a uniquely accessible view of the relativistic processes that shape cosmic evolution on every scale. As modern observatories—from high-resolution X-ray satellites to sensitive radio telescopes—continue to study the system, SS 433 provides ongoing opportunities to refine our understanding of how black holes feed, how jets form, and how extreme gravitational environments sculpt the universe around them. In many respects, SS 433 remains not just an astrophysical curiosity but a cornerstone for testing the laws of physics under conditions that cannot be reproduced anywhere on Earth.

Video credit: X-ray: (IXPE): NASA/MSFC/IXPE; (Chandra): NASA/CXC/SAO; (XMM): ESA/XMM-Newton; IR: NASA/JPL/Caltech/WISE; Radio: NRAO/AUI/NSF/VLA/B. Saxton. (IR/Radio image created with data from M. Goss, et al.); Image Processing/compositing: NASA/CXC/SAO/N. Wolk & K. Arcand; Sonification: NASA/CXC/SAO/K.Arcand, SYSTEM Sounds (M. Russo, A. Santaguida)

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The Neutron Star Interior Composition Explorer (NICER) is a NASA mission launched in June 2017 and mounted on the International Space Station (ISS). Its primary objective is to study neutron stars—ultra-dense remnants of massive stars that have undergone supernova explosions. By observing X-ray emissions from these celestial objects, NICER aims to provide insights into their internal structures and the fundamental physics governing matter under extreme conditions.

NICER’s core component is the X-ray Timing Instrument (XTI), designed for high-precision timing and spectroscopy of soft X-rays in the 0.2–12 keV energy range. The XTI comprises 56 co-aligned X-ray concentrator optics, each paired with a silicon drift detector. These concentrators utilize grazing-incidence optics with 24 nested mirrors to focus incoming X-rays onto their respective detectors, enhancing sensitivity and resolution.

NICER is mounted on the ISS’s ExPRESS Logistics Carrier-2. It features a two-axis pointing system that allows the instrument to track celestial targets across the sky. An integrated star tracker ensures precise alignment, enabling NICER to observe multiple targets during each 92-minute orbit of the ISS.

To achieve its scientific goals, NICER incorporates a GPS-based timing system capable of tagging photon arrival times with sub-microsecond accuracy. This high temporal resolution is crucial for studying the rapid rotational periods of pulsars and other time-sensitive phenomena.

NICER has significantly advanced our understanding of neutron star interiors by providing precise measurements of their masses and radii. These observations have helped constrain the equation of state for ultra-dense matter, shedding light on the behavior of matter at densities exceeding those found in atomic nuclei.

An extension of NICER’s mission, known as SEXTANT (Station Explorer for X-ray Timing and Navigation Technology), successfully demonstrated the use of X-ray pulsars for autonomous spacecraft navigation. By measuring the timing of X-ray pulses from known pulsars, SEXTANT was able to determine the ISS’s position in space, paving the way for future deep-space navigation systems.

In 2018, NICER discovered an X-ray pulsar in the fastest known stellar orbit, with a companion star completing an orbit every 38 minutes. This finding provides valuable data on the dynamics of compact binary systems and the extreme gravitational environments in which they exist.

NICER observed the brightest X-ray burst ever recorded from the neutron star SAX J1808.4−3658. This event offered insights into thermonuclear processes on neutron star surfaces and the mechanisms driving such energetic emissions.

Although primarily focused on neutron stars, NICER has also contributed to black hole research. It mapped “light echoes” from the stellar-mass black hole MAXI J1820+070, revealing changes in the size and shape of the surrounding accretion disk and corona. These observations enhance our understanding of black hole accretion processes and their immediate environments.

In May 2023, NICER’s thermal shields developed a leak, allowing stray light to interfere with its X-ray detectors. To address this issue, NASA designed specialized patches delivered to the ISS via the Cygnus NG-21 resupply mission in August 2024. Astronauts successfully applied these patches during a spacewalk on January 16, 2025, restoring NICER’s full observational capabilities.

As of early 2025, NICER has contributed to over 300 scientific publications, underscoring its significant role in advancing astrophysical research. Its high-precision measurements continue to provide valuable data for the scientific community, enhancing our understanding of neutron stars and other cosmic phenomena.

Video credit: NASA Goddard

Asteroid (52246) Donaldjohanson is a small but significant body located in the main asteroid belt between Mars and Jupiter. Though it may not have the fame of larger or more compositionally unique asteroids, Donaldjohanson stepped into the scientific spotlight thanks to its pivotal role in NASA’s ambitious Lucy mission — a 12-year journey to explore the Trojan asteroids that share Jupiter’s orbit. Before Lucy reaches its primary Trojan targets, it first encountered Donaldjohanson, making it a key object of study in humanity’s effort to understand the solar system’s early history.

Discovery

Asteroid Donaldjohanson was discovered on March 2, 1981, by astronomer Schelte “Bobby” Bus at the Siding Spring Observatory in Australia. Initially designated 1981 EQ5, the asteroid was later named in honor of Dr. Donald Johanson, the paleoanthropologist best known for co-discovering the fossilized remains of Australopithecus afarensis, famously known as Lucy, in Ethiopia in 1974.

This naming decision was particularly meaningful to NASA, as their Lucy spacecraft, launched in 2021, carries a similar goal: to uncover the fossils of the solar system—namely, the Trojan asteroids, which are thought to be leftover building blocks from planetary formation. Naming the asteroid after Johanson creates a poetic link between the exploration of human origins and the origins of our solar system.

Location and Characteristics

Donaldjohanson resides in the inner region of the main asteroid belt, at a semi-major axis of approximately 2.39 astronomical units (AU) from the Sun. Its orbit is relatively circular and stable, with a low eccentricity and inclination, placing it within the Erigone asteroid family, a large group of stony asteroids in the inner main belt.

Though smaller and less well-studied than some of its larger neighbors, Donaldjohanson’s value lies in its convenience and timing—it is perfectly positioned to serve as a flyby target for the Lucy spacecraft en route to the outer solar system.

The Lucy Mission Flyby

NASA’s Lucy spacecraft has successfully completed a flyby of asteroid Donaldjohanson, providing unprecedented insights into this intriguing celestial body. Lucy performed a close flyby at a distance of approximately 600 miles (960 kilometers), capturing detailed images and data.

The flyby is particularly exciting because very few main belt asteroids have been visited by spacecraft, and each one offers a new data point in understanding the diversity and history of these primitive bodies. By studying Donaldjohanson, Lucy will help bridge the scientific gap between the inner and outer asteroid populations.

During the flyby, Lucy used its three onboard science instruments — L’LORRI (a long-range imager), L’Ralph (a visible and infrared spectrometer), and L’TES (a thermal emission spectrometer) — to examine Donaldjohanson’s surface geology, composition, and thermal properties. In addition to gathering scientific data, the flyby allowed engineers to practice operating the spacecraft’s pointing, tracking, and data-gathering systems ahead of the more complex Trojan encounters.

The flyby revealed that Donaldjohanson is a contact binary asteroid, characterized by two lobes connected by a narrow neck, resembling a peanut or a barbell. This structure suggests a history of two separate bodies gently colliding and merging. The asteroid measures about 8 kilometers in length and 3.5 kilometers at its widest point, larger than previously estimated.

Donaldjohanson’s surface exhibits a complex geology with varying crater densities between its lobes, indicating a diverse collisional history. These observations provide valuable data on the processes that shaped such bodies and, by extension, the early solar system. The successful flyby serves as a critical rehearsal for Lucy’s upcoming encounters with Trojan asteroids near Jupiter, scheduled between 2027 and 2033.

Looking Ahead

While Donaldjohanson is not the primary target of Lucy’s mission, the asteroid plays an essential role in validating the mission’s capabilities and providing early science returns. Its proximity and well-known orbit make it an ideal testbed. Moreover, the data collected during the flyby will contribute to our broader understanding of asteroid families, space weathering, and solar system evolution.

After the 2025 encounter, Lucy will go on to visit eight Trojan asteroids, including Eurybates, Polymele, Leucus, Orus, and the binary pair Patroclus and Menoetius. These objects are expected to reveal new insights into the formation of the gas giants and the migration of planets during the early stages of solar system development.

In this grand journey, asteroid Donaldjohanson acts as the first stepping stone—a humble but crucial waypoint on the path to uncovering our solar system’s ancient past. As such, it not only honors the legacy of scientific discovery associated with its namesake but also propels forward the exploration of space’s most enduring mysteries.

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The night sky on Mars shares some familiar features with what we see from Earth, but also presents a few dramatic differences. Since Mars is farther from the Sun than Earth, its sky becomes darker more quickly after sunset, revealing a clearer and more brilliant canopy of stars. With a thinner atmosphere and less light pollution, the stars on Mars appear sharp and more numerous to the naked eye. The Milky Way stretches across the sky much like it does on Earth, but with a bit more clarity due to the reduced atmospheric scattering.

One of the most striking differences in the Martian night sky is the presence of its two small moons, Phobos and Deimos. These irregularly shaped satellites are far smaller than Earth’s Moon, so they don’t dominate the sky in the same way. Phobos, the closer and faster-moving moon, rises in the west and sets in the east in just over 4 hours, appearing several times in a single Martian night. It looks like a bright star or a small disk moving rapidly across the sky. Deimos is smaller and more distant, moving slowly and appearing like a faint star that drifts lazily overhead.

Because of Mars’ distance from Earth, familiar constellations still appear in similar patterns, though slightly shifted. From the Martian perspective, Earth is just a bright bluish “star” in the sky, never appearing larger than a dot without a telescope. Depending on the season and viewing direction, other planets like Jupiter, Saturn, and Venus are also visible, and occasionally even brighter than they are from Earth. Meteor showers can still be seen on Mars, though they originate from different sources due to the planet’s unique orbit.

Another beautiful phenomenon visible on Mars is the aurora, which unlike Earth’s polar-focused light displays, can occur all over the planet due to Mars’ lack of a global magnetic field. These auroras are typically ultraviolet and would require special instruments to see, but they add to the mysterious charm of Martian nights. Overall, the Martian sky offers a uniquely serene and otherworldly view of the cosmos, blending the familiar with the alien in a way that’s both humbling and awe-inspiring.

Video credit: NASA/JPL-Caltech/MSSS/ESO/Bill Dunford

NASA dicit:

This is a sonification of X-ray light emitted by the Crab Nebula. The data was obtained by NASA’s NuSTAR and Chandra space observatories, whose teams turned the data into sound to enable people to audibly perceive different features of the Crab Nebula, making it more accessible for the visually impaired.

In this sonification, X-ray wavelengths from NuSTAR (represented as different colors) are mapped to different musical pitches and sounds. Red, yellow, purple, blue, and white are mapped to notes from low to high. For Chandra, brightness in the X-ray data corresponds with pitch and volume, and a bell sound indicates the position of the pulsar at the center of the nebula.

The Crab Nebula is what remains of a star that exploded as a supernova. The explosion that created the Crab Nebula was visible from Earth in the year 1054, when it was recorded by Chinese astronomers. Most of the star’s mass was pushed into space, creating a wide debris field that continues to expand.

The rest of the stellar material collapsed into a dense object called a pulsar. The pulsar’s rapid rotation and strong magnetic field accelerate particles and shoot them into space.The particles emit high-energy X-rays that NuSTAR can detect, but as they travel outward, they collide with the debris scattered by the supernova, causing them to slow down and lose their energy. This is why NuSTAR only sees light from a relatively small region close to the pulsar. Lower energy X-rays detected by Chandra can be seen farther out.

Video credit: NASA/JPL-Caltech/CXC/SAO

Wikipedia dicit:

The Fermi Gamma-ray Space Telescope (FGST, also FGRST), formerly called the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts and solar flares.

Fermi, named for high-energy physics pioneer Enrico Fermi, was launched on 11 June 2008 aboard a Delta II 7920-H rocket. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden, becoming the most sensitive gamma-ray telescope on orbit, succeeding INTEGRAL. The project is a recognized CERN experiment (RE7).

Video credit: NASA Goddard