Erika
@ExploreCosmos_ • 60,176 subscribers
Canadian astrophysicist focused on extragalactic astronomy & early-universe galaxies. Seeking mountain peaks. Writing through the chaos; riding away from it.
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Astronomers have discovered an extraordinary star orbiting Sagittarius A*, the supermassive black hole at the centre of the Milky Way, on the most extreme stellar orbit observed there so far. The star, designated S301, was identified using the GRAVITY instrument and its upgraded GRAVITY+ system on ESO’s Very Large Telescope Interferometer in Chile. What makes S301 particularly important is not simply its enormous speed, but how deeply its orbit carries it into the strongly curved spacetime surrounding the black hole. S301 completes one orbit in only about 8.7 years, the shortest known period for a star around Sagittarius A*, and during its closest approach it passes roughly 1.78 billion kilometres from the black hole, only about 12 times the Earth–Sun distance and comparable to the distance between Saturn and the Sun. At that point it reaches around 25,000 km/s, more than 8% of the speed of light, making it the fastest known star in the Milky Way. Sagittarius A* contains approximately 4.3 million times the mass of the Sun, compressed into a region small enough to behave observationally as a black hole. Astronomers have been studying stars around it for decades because their trajectories provide exceptionally clean tests of gravity. The most famous example is S2, whose 16-year orbit has already allowed researchers to detect gravitational redshift and relativistic orbital precession exactly where general relativity predicts them. S301 takes this experiment much further. Its orbit is extremely elongated, with an eccentricity of about 0.98, and at pericentre it approaches Sagittarius A* roughly ten times more closely than S2 in terms of Schwarzschild radii. The resulting relativistic effects should therefore be considerably stronger. The most interesting consequence is that S301 may allow astronomers to directly measure the spin of Sagittarius A*. According to general relativity, a rotating black hole does not simply curve spacetime through its mass; its rotation also drags the surrounding spacetime with it. This phenomenon, known as frame dragging or the Lense–Thirring effect, produces an additional precession in the orbit of an object moving close to the black hole. The effect becomes rapidly weaker with distance, which is why it has been extremely difficult to detect using previously known stars around Sagittarius A*. S301 travels close enough that the change in its orbit caused by the black hole’s rotation may become measurable within roughly the next decade. Importantly, the researchers have not yet measured the spin of Sagittarius A* from S301. Rather, they have discovered a star whose orbit is sensitive enough to that spin that such a direct measurement may now be realistically achievable. The discovery was technically difficult because S301 is extraordinarily faint. In the infrared K band it has a magnitude of about 19.3, and ESO notes that it appears roughly two billion times fainter than Betelgeuse in the sky. GRAVITY achieves the necessary angular resolution by combining the light from four 8.2-metre Unit Telescopes of the VLT through interferometry, effectively producing a virtual telescope with far greater resolving power than any individual telescope. The team first clearly identified S301 in observations from 2023 and subsequently followed it during 2024 and 2025. Once its preliminary orbit was established, astronomers were able to trace it retrospectively in earlier data from 2021 and even find evidence for it in observations obtained in 2017. Altogether, 19 astrometric measurements were used to constrain its orbit. There is still an important limitation: S301 is currently too faint for researchers to obtain a reliable spectrum and radial velocity. Without that information, two possible three-dimensional orientations of its orbit remain compatible with the observations. Future instruments should resolve this problem. In particular, MICADO on ESO’s Extremely Large Telescope should be sensitive enough to obtain spectroscopy of S301 and determine its radial velocity, while continued observations with GRAVITY+ will refine its astrometry. Its next pericentre passage is expected in 2031, and observing at least two complete orbits should give researchers the precision needed to search for the subtle additional precession produced by the spin of Sagittarius A*. S301 may also provide clues about how stars end up so close to a supermassive black hole. Stars are unlikely to form normally at such small distances because the black hole’s tidal forces make the collapse of ordinary star-forming clouds extremely difficult. The researchers instead favour a scenario involving the Hills mechanism. S301 may originally have belonged to a tight binary system that approached Sagittarius A*. The black hole’s tidal gravity could have torn the binary apart, capturing S301 onto its present highly eccentric orbit while ejecting its companion at enormous velocity, potentially fast enough for that star to escape the Milky Way entirely. The observed orbit of S301 is consistent with this interpretation. The importance of the discovery therefore goes beyond setting a speed record. S301 effectively acts as a natural test particle moving through one of the strongest gravitational fields that astronomers can study using individual stars. Tracking its motion could provide the first direct stellar-dynamical measurement of the rotation of Sagittarius A*, improve tests of general relativity in the strong-field regime and, over longer timescales, potentially probe more subtle properties predicted for rotating Kerr black holes. Instead of observing the black hole itself, we can use the trajectory of S301 to map how Sagittarius A* deforms and twists the spacetime around it. 👉
Erika 299,370 views • 11 days ago
NASA’s Habitable Worlds Observatory: the telescope designed to search for another Earth. NASA is already developing the technologies for what could become one of the most ambitious astronomical observatories ever built. The Habitable Worlds Observatory, or HWO, is being conceived as NASA’s next major flagship astrophysics mission after the Nancy Grace Roman Space Telescope. Its defining objective is extraordinarily simple to state and extraordinarily difficult to achieve: directly photograph rocky planets similar to Earth around nearby Sun-like stars and analyze their atmospheres for evidence that some of them might support life. NASA’s current science goal is to directly image and characterize roughly 25 potentially habitable worlds. HWO is not simply a larger version of Hubble or Webb. It combines lessons from Hubble, JWST and Roman with technology developed during the earlier LUVOIR and HabEx mission studies. NASA is currently exploring several possible architectures rather than committing to a final telescope design. The engineering concepts being studied include a 6-meter segmented off-axis telescope, another 6-meter configuration using a central keystone-shaped mirror surrounded by segments, and an 8-meter on-axis design. NASA explicitly warns that none of these should yet be interpreted as the final appearance of HWO. The reason such a large telescope is required becomes obvious when we consider what HWO is trying to see. An Earth-like planet observed in reflected visible light can be approximately ten billion times fainter than its host star. Worse, from tens of light-years away the planet appears extremely close to that star in the sky. HWO must therefore separate two sources that are both enormously different in brightness and separated by only a tiny angle. It is rather like trying to detect an extraordinarily faint point of light immediately beside a searchlight, except that both are light-years away. NASA’s technology development is consequently aimed at contrasts approaching 10⁻¹⁰. The baseline solution is an extremely advanced coronagraph located inside HWO. A coronagraph suppresses the light from the star while allowing light from surrounding planets to reach the detector. This sounds straightforward, but at a contrast of one part in ten billion, tiny imperfections in the optical system become important. Minute distortions of a mirror can scatter enough starlight into the image to imitate or completely hide a planet. HWO will therefore combine coronagraphic masks with deformable mirrors, precision wavefront sensing and active wavefront control to create an exceptionally dark region around the stellar image where planets can be detected. NASA refers to the process of creating this high-contrast region as digging a coronagraphic “dark hole.” This is why HWO also needs to be one of the most optically stable spacecraft ever constructed. NASA says its optical system may need to remain stable at scales comparable to the width of an atom, while wavefront control requirements reach into the picometer regime. Thermal changes, mechanical vibration, reaction-wheel disturbances, structural creep and even very small motions between individual primary-mirror segments can destroy the contrast required to see an Earth analogue. Technologies under development therefore include ultra-stable mirror assemblies, extremely stiff structures, millikelvin-level thermal control, low-disturbance mechanisms, precision segment sensing and control, vibration isolation and microthrusters. One of the most visually striking technologies associated with HWO is the huge flower-shaped starshade seen in many NASA demonstrations. The flower shape is not decorative. A starshade is an external occulter: instead of blocking the star inside the telescope, an independent spacecraft places an enormous opaque screen between the telescope and the target star. The telescope then sits inside the extraordinarily dark shadow created behind it while the light from planets located slightly to either side of the star continues past the shade and reaches the telescope. A simple circular disk would not work well enough because light diffracts around its edge. In fact, diffraction would partially refill the shadow with stellar light. The strange elongated petals are engineered specifically to manipulate that Fresnel diffraction pattern. Their carefully calculated edges make the transition between opaque and transparent space gradual from the point of view of the propagating wavefront, dramatically suppressing diffracted starlight in the central shadow. In other words, the “flower” exists because of wave optics: each petal contributes to shaping the diffraction field so that the telescope occupies a region where the stellar electric field is almost cancelled. NASA laboratory demonstrations have already achieved broadband starshade contrasts below approximately 10⁻¹⁰ at flight-like Fresnel numbers. A flight starshade for an observatory such as HWO would be enormous. Different concepts range from roughly 35 to 60 meters or more in diameter, while experimental NASA concepts have investigated sizes approaching 100 meters for other applications. It would fly tens of thousands of kilometers from HWO; current technology studies commonly consider separations of order 100,000 km, depending on starshade diameter and wavelength. Both spacecraft would have to maintain extremely accurate alignment with the target star while effectively operating as a single optical instrument across an enormous baseline. There is an important distinction, however. NASA currently plans HWO around an internal coronagraph, not around a starshade. Coronagraphs have major operational advantages: they are integrated into the telescope, can move rapidly from one target to another and do not require a second giant spacecraft to reposition itself across interplanetary-scale distances. A starshade, by contrast, would require substantial propulsion every time it moved between target stars and would introduce another complex spacecraft and formation-flying system. Nevertheless, NASA continues to study starshades because they have attractive properties. They suppress starlight before it enters the telescope, are relatively insensitive to many telescope optical imperfections and could extend HWO’s scientific capability, potentially including wavelengths where internal coronagraphy becomes particularly challenging. NASA has even studied launching such a system separately and allowing it to rendezvous with a telescope later in its mission. Once HWO has isolated the light from an exoplanet, simply obtaining a photograph will not be the most scientifically important part. The crucial information will come from spectroscopy. By separating the planet’s reflected light into its constituent wavelengths, HWO could identify absorption produced by molecules in its atmosphere. Water vapor could provide information about habitability, while gases such as oxygen, ozone and methane could become part of a search for possible biosignatures. No single molecule would constitute proof of life: atmospheric chemistry has abiotic pathways capable of producing potentially misleading signals, so HWO will need to study combinations of gases together with the planet, its star and the wider planetary environment. Its wavelength coverage is therefore fundamental. HWO is being developed as an ultraviolet, optical and infrared observatory. In addition to visible and near-infrared measurements of exoplanets, ultraviolet capability can reveal species such as ozone and provide information about stellar radiation and atmospheric photochemistry. NASA is consequently developing high-efficiency UV detectors, advanced mirror coatings, ultraviolet gratings and filters, low-noise visible detectors and photon-counting technologies capable of extracting extremely small numbers of photons from distant planets. Some of the relevant observations will be so photon-starved that obtaining a useful spectrum of a single world could require very long integrations. The telescope will also be a general-purpose astrophysical observatory. Just as Hubble became far more scientifically important than any single problem it was originally designed to solve, HWO is intended to study everything from nearby stellar and planetary systems to galaxy evolution and the distant universe. Its combination of a large aperture, diffraction-limited imaging and ultraviolet-to-near-infrared spectroscopy would give astronomers capabilities unavailable from either Webb or ground-based observatories. Another unusual aspect of the architecture is longevity. NASA is planning HWO to operate near the Sun-Earth L2 region and to be robotically serviceable. Instruments could potentially be repaired or replaced and consumables replenished, allowing the observatory to evolve technologically rather than remaining frozen in the configuration it had at launch. That capability could also make a later-generation coronagraph, new detectors or potentially complementary technology such as a starshade scientifically relevant decades after HWO first begins operating. HWO remains in its technology and mission-maturation phase. NASA is deliberately exploring the trade space before fixing the final architecture, with major work continuing on coronagraphs, deformable mirrors, telescope stability, detectors, UV instrumentation, deployable structures and servicing technology. Current NASA planning aims to mature many of the enabling technologies around the end of this decade, while a launch is generally discussed for around 2040 or in the 2040s rather than as a fixed launch date. In January 2026 NASA awarded additional industry contracts specifically to advance key HWO technologies, showing that the project has moved beyond a purely hypothetical observatory even though its final design has not yet been selected. If HWO succeeds, its most memorable image may not initially look very spectacular: perhaps only a tiny pale dot beside a carefully suppressed star. But contained inside the spectrum of that dot could be water, clouds, atmospheric chemistry and, potentially, the first observational evidence that biology is not unique to Earth. The central technological problem of HWO is therefore not simply building a bigger telescope. It is learning how to remove almost every photon from a nearby star while preserving the vanishingly small number of photons arriving from a planet beside it. The coronagraph, the picometer-stable telescope and perhaps one day that enormous artificial flower flying tens of thousands of kilometres away are all different solutions to that same problem. Video: This is one of the technologies being investigated for future direct imaging of Earth-like worlds and potentially for use with HWO. Not necessarily the final design.
Erika 56,926 views • 23 days ago
The final parsec problem presents a significant challenge in astrophysics, particularly in the study of the coalescence of binary black hole systems. This problem arises from the inefficiency of gravitational wave emission in driving the black holes together once ... 1/
Erika 454,643 views • 2 years ago
Researchers at Tokamak Energy have captured for the first time a real-time, high-speed video of plasma behaviour inside their ST40 spherical tokamak, tracking visible green and red light emissions as the fusion process occurs. This visual insight comes via a camera operating at thousands of frames per second, offering unprecedented detail of how the plasma evolves, interacts with the surrounding lithium blanket and outer regions, and ultimately radiates energy. The imaging enables scientists to observe how the ultra-hot core transitions outward into cooler zones, how magnetic confinement shapes the plasma behaviour, and how impurities or outer-region interactions influence the process. By giving a ‘star-in-a-donut’ view of fusion in action, this breakthrough adds a new diagnostic tool to the development of fusion energy, helping engineers refine the magnetic confinement, optimise plasma stability and better understand the heat and light flows at play. It was slowed down by 100x. All this was for 0.3s A tokamak is one of the most advanced devices ever created to achieve controlled nuclear fusion, the same process that powers the Sun. Its goal is simple in principle but incredibly challenging in practice: heat a gas until it becomes plasma, raise that plasma to over 100 million degrees, and confine it long enough for hydrogen nuclei to fuse and release energy. Because no material container can survive such temperatures, a tokamak uses powerful magnetic fields to hold and shape the plasma like an invisible cage. The device has a distinctive doughnut-shaped (toroidal) chamber surrounded by magnetic coils. When the machine is switched on, electric currents and external magnets work together to create helical magnetic fields that trap the plasma and keep it away from the walls. As the plasma spirals around these magnetic lines, it heats up dramatically. Additional heating comes from methods like radio-frequency waves and neutral-beam injection, pushing the plasma toward the extreme temperatures needed for fusion. Inside this tightly controlled environment, hydrogen isotopes such as deuterium and tritium can collide and fuse, releasing fast neutrons and a burst of energy. The goal of tokamak research is to reach a point where the fusion reactions produce more energy than the system consumes, a milestone known as “net energy gain.” Modern machines like ITER, JET, and Tokamak Energy’s ST40 are bringing this vision closer, using advanced diagnostics, superconducting magnets, and increasingly stable plasma control. 👉
Erika 162,540 views • 9 months ago
Gotta love geometry 💚 This dodecagon can be split into pieces and put back together as three equal squares, each one using the radius as its side. That works because its 12 sides are all the same length and repeat in a perfect pattern. Ancient mathematicians, like Euclid, discovered that some shapes can be “taken apart” and “put back together” to show their area in a simpler way. So in the end, the area of a dodecagon is basically like combining three squares made from its radius. #Math #Geometry
Erika 110,547 views • 9 months ago
The Milky Way is nothing else, but a mass of innumerable stars planted together in clusters. ~Galileo Galilei~ The planets orbit the Sun, roughly in the same plane. The Solar System moves through the galaxy with about a 60° angle between the galactic... 1/2 ©️ YT / DjSadhu
Erika 297,862 views • 2 years ago
Earth is approaching a stream of debris from Halley's Comet, source of the Orionid meteor shower. Forecasters expect the shower to peak on Sun, Oct. 22nd, with 15/20 meteors/h. The best time to look is during the dark hours before sunrise when Orion the Hunter is high in the sky.
Erika 185,819 views • 2 years ago
Distance to some galaxies from the Milky Way. 1 light year = 9.5 trillion km.
Erika 84,948 views • 1 year ago
The Lagrange points, named after the French mathematician Joseph-Louis Lagrange, are unique locations in space where gravitational forces create a delicate equilibrium btw the gravitational pull of 2 large celestial bodies, such as a planet & its moon or a planet & the sun. 1/
Erika 106,766 views • 2 years ago
It is already known that the configuration of our Solar System, a single star with planets around it, is something that is not really a standard in our Galaxy. A lot of Systems have two Stars, for example, a binary system, and there are even weirder ones with many stars. In Comparison, our System seems boring. 🥱 📹 morn1415
Erika 80,517 views • 1 year ago
A new study has provided compelling evidence that Earth, shortly after its formation, was initially dry and lifeless, lacking the essential building blocks for life, such as water and organic compounds. Using precise measurements of the radioactive decay of manganese-53 into chromium-53 in meteorites and terrestrial rocks, the researchers determined that Earth's basic chemical composition was established within roughly three million years after the Solar System formed. This finding supports the Giant Impact Hypothesis: Earth’s Moon formed when a Mars-sized body, dubbed Theia, collided with our planet about 4.5 billion years ago. Crucially, Theia appears to have originated farther out in the Solar System and carried volatile elements, including water and carbon-rich compounds, that Earth lacked at the time. Therefore, it seems that Earth’s habitability, and ultimately the emergence of life, was not a straightforward outcome of gradual development but rather hinged on this dramatic, chance impact. 👉
Erika 45,023 views • 1 year ago
Astrophotographer Mark Johnston Azastroguy captured a mesmerizing scene on October 20, 2025, from Willow Springs Lake in Arizona, showing a fiery filament of hydrogen plasma dancing above the Sun’s limb. Suspended by the Sun’s magnetic field, this structure twists and shimmers in a 6.5-second time-lapse video that condenses 75 minutes of real solar activity. Using a TEC 160FL refractor equipped with specialized solar filters, including a 0.3 Å hydrogen-alpha etalon, Johnston revealed an extraordinary level of detail in the solar prominence, a glowing loop of magnetized gas rising from the photosphere into the corona. The footage captures the intricate motion of plasma arcing hundreds of thousands of kilometers across the Sun’s surface, sometimes lasting for days or even weeks. Beyond its beauty, the video serves as a reminder of the Sun’s dynamic magnetism and the importance of using certified solar filters, since observing the Sun without protection can cause permanent eye damage.
Erika 37,056 views • 10 months ago
